Engine transplants - Clutch and flywheel assemblies

by Keith Calver 20. August 2005 11:24

Terminology -
BBU - Big Bore Units
SBU - Small Bore Units

NOTE: This information is largely concerned with transplanting a large-bore engine into a small-bore engined Mini. For further information on clutch and flywheel assemblies in particular, refer to relevant separate article.

To go in to all the possible permutations would take a few chapters on it’s own. Suffice to say that the Metro had a few weirdo fitments such as cable operation, an in-line ‘damper’ (some got fitted to Minis too - eek), and ‘top-hat’ plunger and rod bearing operation. The Mini only has two - pre-Verto multi-piece and Verto (Valeo in some instances but exactly the same otherwise). The easiest solution is to use the whole system as fitted to your Mini. On no account try to adapt Metro stuff to fit the Min unless it’s to use the Metro Verto flywheel set-up, in which case all Mini Verto operating linkage is needed. Don’t try to cross-pollinate the two Mini systems either. It can be made to work sometimes, but is too hit and miss and a whole bunch of aggravation. Up-grade from SBU parts to BBU ones to cope with the extra power (as detailed in the relevant article).

By ‘linkage’ I’m referring to all components carried/housed in the clutch cover - also referred to as 'wok' and 'end cover' - and slave cylinder/mountings. The Mini clutch MASTER cylinder is the same throughout. So where a Mini or Metro Verto-type flywheel assembly is being used in a pre-A+ engined Mini, get the cover assembly and slave cylinder off an A+-engined model. Likewise, if using the earlier multi-piece flywheel assembly in an A+-engined Mini, you need the pre-A+ clutch cover assembly and slave cylinder. The actual covers are the same and swappable, it’s all the gubbins that’s different. Strip it all down before fitting and check the pins/arm/plunger for wear.

The clevis pins are cheap to replace, so new ones are a good idea. The push-rod clevis pin hole can elongate, again cheap so replace it. The plunger wears on the inside where the lever-arm pushes against it. A severe concave recess here means a new one is needed. There are three types of plunger/bearing assembly. Earlier ones have a press-fit release bearing, intermediate ones were 'floating' held on by a spring clip, the latest a multi-piece release bearing held on by an ‘O’ ring. The first two are interchangeable the last not. Wear on the lever-arm is usually on the ball at its base. This pushes the plunger in. If there’s a flat worn on it, replace it otherwise it won’t disengage the clutch properly. Now, the long pre-Verto arm is quite cheap - not so the short Verto one. Try to obtain a good second-hand one, or take a good stiff swig of Brandy before asking the price of a new one! This arm can be sourced from Metros as well as Minis - so take heart!

Wear on this ball causes clutch malfunction because of the leverage ratios involved. When very worn it causes the slave cylinder piston to reach the stop-ring before the clutch properly disengages. A quick-fix if a new arm is unaffordable/not forthcoming is to extend the push rod where it goes into the slave cylinder by welding a short piece to it (cut off bolt, small nut, almost anything that’ll fit in the slave cylinder orifice). It’s also possible to bend the long arm by heating it up above the stop knuckle and bending it towards the slave cylinder face slightly. Don’t over do either of these as the ball will bend backwards (and possibly break off) rendering the clutch completely inoperable. REMEMBER - they’re only quick fixes, change it at the earliest opportunity. Adjust the clutch stops as per a manual once the unit is refitted.

Carefully grease all the parts when reassembling using a multi-purpose grease, and make sure the clutch plunger is fitted the right way - big chamfered hole uppermost - to avoid breaking the ball off!

Useful part numbers:
Clutch plunger Press fit brg. 22A180
Floating brg. DAM1955 - retaining clip DAM2413
Late type DAM5353 - retaining O ring AAU2866
Clutch release bearing Press/floating GRB201
Late type GRB239
Clutch arm Pre Verto 22A2204 - long type
Verto DAM5355 - short type
Clevis pins Large CLZ628 - fits both
Small CLZ518 - fits both
Clutch arm push-rod Both 13H396
Clutch slave cylinder Pre Verto GSY110
Verto GSY118
Clutch master cylinder All GMC1008

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Clutch | Engine

Engine transplants - Ancillary parts

by Keith Calver 20. August 2005 10:37

Engine mountings are a whizz to fit as the Mini ones fit straight onto any of the other units. Just remove the Metro/AA/1300GT ones and swop the mounts over from the Mini unit. If they’re split, fit new ones, they’re cheap.

Terminology -
BBU - Big Bore Unit
SBU - Small Bore Unit

NOTE: This information covers transplanting large-bore engine units into small-bore engined Minis. For further information for exact differences between pre-A+ and A+ units, see relevant separate article.

Engine mountings and steady bars.
Engine mountings are a whizz to fit as the Mini ones fit straight onto any of the other units. Just remove the Metro/AA/1300GT ones and swop the mounts over from the Mini unit. If they’re split, fit new ones, they’re cheap. If using the AA/1300GT unit - it's advisable to cut off the 'wings' on the front plate that carried the engine mounts on the radiator end. They get in the way otherwise. As for engine steadies, fit up-rated bushes to the standard one from block to master cylinder plate. The one fitted to most late Minis going from the bottom of the clutch case forwards is a waste of space unless you weld a washer to the bracket to remove possible slop caused by the elongated bolt hole. Far better is the one that fits this end and goes rearwards to the subframe leg; and it’s companion that fits on the left side to the speedo drive case, likewise trailing to the rear subframe leg. Ultimately the competition-type top engine steady from thermostat housing to bulkhead cures all ills in this department.

In all applications now though, the introduction of the injected cars has thrown a new spanner in the works. The subframes used in these cars have the engine moved forward some 3/4" in the subframe. So if you've recently fitted a new subframe from a very latest spec car - you're going to need to extend all the engine steady bars!

Some 'doctoring' of the timing cover breather where fitted is necessary to assist clearing the fan blade. Use a hammer to flatten it where it faces the fan. Use of a small spacer (available as a separate part) between the fan and pulley also helps alleviate the clearance problem. Make sure you fit the fan the right way round - smooth, sculpted-centre side towards the pulley. Use whichever fan belt suits the water-pump pulley, as many Metros had an oversized pulley to reduce pump speed (a worthy idea).

Metros use 5/8” heater pipes so conversion to Mini-type cooling makes things easier, tidier, and more effective. Use the Mini thermostat housing together with a Cooper S top radiator bracket - the thermostat housing angle is different on the BBU - and Cooper S or 1275GT top hose. Drill the heater tap take-off through - the recess is there in Metro heads as are the tapped bolt holes (1/4” UNF thread) to retain the heater tap. Don’t bother plumbing in the inlet manifold if the MG Metro heated type is used - colder intake temperature gives more power! To allow water to circulate prior to the thermostat opening in the absence of a by-pass hose (Metros use a sandwich plate under the thermostat housing) drill 6 1/8” holes around the thermostat’s perimeter.

I would highly recommend fitting a new radiator - the standard Mini one just about copes with the standard engine. Bigger/more powerful engines generate more heat; a brand new standard rad will be hard pressed. Use one of the hi-tech 2-core units; the expense is worth it - cheaper than a melt down!

Starter motors.
If using the flywheel assembly from the SBU out of the car, use the starter too. Going Verto from pre-Verto, count the ring gear teeth. 107 will mean you can use the Mini inertia-type starter, 129 means it’s for a pre-engaged set up. The Metro pre-engaged starter doesn’t fit a Mini, so a Mini one is needed. This may prove very expensive, and re-wiring is necessary as the solenoid is part of the starter. A cheaper way is to fit the relevant ring gear. If fitting a BBU to a Mini with pre-engaged starter, and intend using the early flywheel set up it is possible to retain the 107 tooth ring gear. The engine will spin over quicker and make an odd noise, but it will work. Unfortunately service life will be much reduced. Change the ring gear - it’s cheaper in the long run!

Gear linkage
In post 1973 cars where rod-change-type gearboxes are being fitted in place of a remote-type system, use the entire linkage and gearlever system from the late Mini if it has to be sourced separately. The older remote fits in a semi-circular shaped tunnel, the rod-change a square one, so brackets or spacers are needed depending on what facilities and components you have to hand. Mini Mania sells a special conversion bracket to simplify matters. The rod-change’s cotton-reel type rear mounts make this very simple to do. The fitting’s not too critical PROVIDING the linkage isn’t fitted under tension fore/aft - it will make the gears jump out. Hang the rods/gearlever housing in their natural position. Trimming of the tunnel hole may be needed too. Sometimes it is, sometimes it isn’t. Fit the linkage and try it first.

NOTE; It is entirely feasible to use the pre-Verto flywheel and clutch assembly with the later pre-engaged (integral solenoid) type starter motor. The best way to accomplish satisfactory fitment is to fit the narrow ring gear of either the Verto flywheel (part no. PSF10003, 129 teeth). However, the standard pre-Verto ring gears (107 teeth) will also work OK with the pre-engaged starter, albeit somewhat noisily that will shorten ring gear and starter bendix life. Where the standard, wide ring gear (0.50-in wide) is fitted, a 0.125-in spacer MUST be fitted between the starter and the transfer gear case to prevent the starter bendix from being permanently engaged. Washers to the value of 0.125-in will be Ok for a short period, a proper, full spacer plate duplicating the starter mounting plate is necessary to ensure long life of the starter. Failure to do this will cause extensive damage to ring gear and starter at the least. The thin ring gear (0.345-in wide, part no.12G2613) such as used on the ultra light and steel lightweight flywheels is used, no spacers are required.

Useful part numbers:
Clutch plunger Press fit brg. 22A180
Floating brg. DAM1955 - retaining clip DAM2413
Late type DAM5353 - retaining O ring AAU2866
Clutch release bearing Press/floating GRB201
Late type GRB239
Clutch arm Pre Verto 22A2204 - long type
Verto DAM5355 - short type
Clevis pins Large CLZ628 - fits both
Small CLZ518 - fits both
Clutch arm push-rod Both 13H396
Clutch slave cylinder Pre Verto GSY110
Verto GSY118
Clutch master cylinder All GMC1008

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Engine transplants - Changing FDs and speedo drive ratios.

by Keith Calver 20. August 2005 10:16

What they don’t tell you in the manual!

Terminology -
FD - Final Drive (diff ratio)

What they don’t tell you in the manual!
If you’ve decided the FD fitted isn’t what you want, changing the FD is possible without separating the engine from the gearbox. Removing the diff case will allow you access to the diff assembly to change the crown-wheel, and access to the gear-change linkage. Use a manual for crown-wheel replacement. While you’re in there it would be just as well to replace the thrust washers and diff-pin as these are the source of many a gearbox problem. Particularly for up-rated engines where fitment for the competition diff-pin is highly recommended. Once again, follow the manual here. Now the bit they don’t tell you how to do...

Rod-change types -
Removal of the speedo drive housing gives access to the pinion retaining nut (1.5”AF socket needed and a long bar). To be able to undo the pinion nut (torqued up to 150lb ft !!) you need to engage two gears - 2nd and 4th - to lock the transmission. Rotate the gear selection barrel anti-clockwise as far as possible then pull it back towards you, i.e. away from the gearbox. Make sure both the inner selector shaft and the outer barrel are as far back as they will go. Using a pry bar, or long screwdriver, push the 1st/2nd and 3rd/4th selector quadrants inwards. They will rotate towards the clutch end, and in so doing engage 2nd and 4th gears. Engaging reverse by sliding the gear away from the centre web and into mesh with the outer gear of the 1st/2nd outer track using a long screwdriver assists further. Through the speedo-housing aperture, use a small chisel to undo the pinion lock tab. Now undo the pinion nut. You are going to need help with this, somebody to hold the engine whilst you heave mightily on the pinion nut! Carefully pry the pinion nut off of the shaft - NOT on the edges of the teeth as they can easily be chipped!

Re-assemble in the exact reverse order, adding the replacement parts, ensuring when you re-engage the selector outer barrel and shaft that all the selector quadrants are in line, especially the reverse gear one as this can not be seen. Test for engagement by pushing and pulling a little on the selector shaft at each quadrant level. You will actually be able to see the reverse lever moving if it is engaged. Then rotate the selector back to its standard position. Re-fit the diff as per the ‘book’. But before refitting the speedo drive housing check the speedo drive compatibility information below.

Remote-change types -
Removing the speedo drive housing gives you access to the gear-change linkage and FD pinion nut. You need to undo the 1/2"AF-headed bolt that holds the gear selector peg in place on the shaft running diagonally down from top right to bottom left of the gearbox as viewed through from the speedo drive housing end. Also remove the neutral-positive location 'claw'. To enable un-going of the pinion nut, two gears have to be selected. Using a suitable rod/heavy screwdriver, push on the ends of the right hand and central gear selector rods. This will select 2nd and top gears, locking the gearbox up. Knock off the pinion lock-tab, and undo the nut. Remove pinion and re-fit replacement, and re-assemble in reverse order making sure all gear selector components are in the correct places/positions, lock-tabs bent over, and all nuts/bolts correctly fitted and tightened. Pinion nut torque setting is 150lb ft. Before replacing the speedo drive housing, check the speedo drive compatibility information below

Speedo drive compatibility
Altering the FD can cause speedo inaccuracies. Whilst being a possible excuse for transgressing speed limits, it probably won’t keep you out of traffic cops notepads. This therefore needs attention.

Prior to 1980, matching FD changes to speedo readings was done by fitting a different speedo, an expensive way of dealing with the problem. After this the mix ‘n’ matching went on in the gearbox. More specifically the speedo drive spindle and pinion. So dealing with the easiest one first, fitment of any A+ gearbox with a 3.44 FD to a pre-A+ powered Mini, you need to fit the spindle and pinion out of the pre-A+ gearbox. Simple. If any other FD is fitted, it is easier and cheaper (in the long run) to get the speedo re-calibrated. Now the multiple choice option...check out the relevant table. This assumes 10” wheels and 12” wheels are retained where fitted as standard, but is reasonably accurate for 13” wheels, as the rolling circumference is very similar.

Speedo drive spindle and pinion data -
Tooth count - Tooth count -
Final Drive Ratio Pinion Colour Part no. Spindle Colour Part no.
All pre-1980 17 white 22A1881 6 none 2A3720
3.44 16 green DAM2905 6 none 2A3720
3.2 18 red TXD1006 5 red TXF1004
3.1 16 green DAM2905 7 blue DAM6028
2.76 15 black TXD10004 7 yellow TXF10001

Useful part numbers:
C-BTA166 Competition diff-pin
BTA101 Diff output thrust washers (2 needed)
2A7062 Pre-A+ located planet-wheel thrust washers (2 needed)
DAM5071 A+ located planet-wheel thrust washers (2 needed)
DAM6624 Planet-wheels (2 needed)
RPS1418 Diff-pin locating roll pin
ATA7385 Crown-wheel bolt lock-tabs (3 needed)
ATA7043 Crown-wheel to diff cage bolts (6 needed)
DAM6140 Pinion lock-tab
GUG705569GM Speedo drive housing gasket
GUG705564GM Speedo drive spindle housing gasket
GUG705565GM Speedo drive pinion housing gasket
2A3505 Upper diff housing gasket, all
2A3506 Lower diff housing gasket, remote change
22G1836 Lower diff housing gasket, rod change
TOOL03 1.5"AF deep 1/2"-drive socket for pinion nut (also does swivel pins and Flywheel bolt)

Engine - Small-bore engine, 12G940 head fitting

by Keith Calver 20. August 2005 10:02

There is no specific large-bore (1275cc-based) head casting number that will fit the 998 engine any easier than any other.

They all have the same problems - generally requiring exhaust valve relief cut-outs machined into the block and re-alignment of the front water gallery transfer ports. However, I would avoid using heads with valves bigger than 35.7mm on the intake since these are too big for most 998 engines unless they are absolutely full-race spec where top end power at high rpm is all that is required.

First of all it is worth checking that you actually need to make the relief cut-outs since some heads have a big enough head face to exhaust valve face clearance to allow fitment without the cut-outs when the standard cam and rocker gear is retained.

If possible, measure the actual valve lift you are getting with the current fitted set-up. Carefully set the valve lash clearance (clearance between valve tip and rocker) to 0.012-in./0.30mm. With an exhaust valve in the fully closed position, position a dial gauge (DTI) on the valve cap, zero the gauge and then rotate the engine until maximum valve lift is achieved - counting the amount of lift indicated by the gauge. This is likely to be around 0.270-in./6.86mm. The maximum you are likely to see is 0.280-in./7.11mm if you have a particularly good set-up since the standard 998 camshaft will only have 0.235-in./5.97mm lift at the lobe, the maximum rocker ratio is likely to be 1.25 - the valve lash setting being taken from the result. So 0.235-in. x 1.25 = 0.294-in., less the 0.012-in. lash setting gives 0.282-in. BUT it is rare that the standard sintered steel rockers give anything like this lift ratio. From personal experience the best to be expected is 1.22 - so the actual nett full lift will be less.

If you can't check the valve lift because the head has already been removed, you will need to check the lift at the cam using a DTI positioned on a push rod placed in one of the exhaust valve followers riding on the camshaft whatever reading you get, multiply this by the rocker ratio and minus the valve lash setting detailed above.

With the 1275 head upside down, accurately measure the depth of the exhaust valve face in comparison to the head face. This measurement needs to be at the very least the same as the exhaust valve lift registered as above. Preferably greater. It is possible to increase this distance by cutting the exhaust valve seats a little further into the head and/or removing material from the face of the exhaust valve. I would only look to gain around 0.030-in./0.76mm by doing this though. Alternatively, going to a race-spec exhaust valve may nett some more clearance since the valve seat edge to valve head face on race valves tends to be less than standard OE type valves. If doing this when using the standard cast iron guides, it is essentially you use either a chromed-stem type competition valve or one of the later nitrocarborised/Tuftrided type valves (charcoal grey/black in appearance.

All of the above is totally affected by camshaft type and rocker gear used. 1.5 ratio rockers simply don't work in general on road-going 998s in my experience so should be avoided. The probable maximum cam lift you may be able to entertain using the above criteria would be 0.250-in./6.35mm as used on the more 'performance' standard profiles such as the MG Metro, standard 1275 Metro and older 998 Cooper and S cams. In which case you'd be looking for around 0.293-in./7.44mm clearance between exhaust valve face and head face to avert using cut-outs.

The head gasket is your safety margin - so don't add this into the equation at any point. Crushed as fitted it gives around 0.028-in./0.71mm to 0.032-in./0.81mm thickness - just enough for that safety margin. Don't ever over-rev the engine or miss a gear-shift though!

And talking of head gaskets - you will need to use the 1275 item to get a reasonable alignment for sealing both the combustion chambers and the front water gallery transfer ports in the head. The 998 head gasket over-hangs the 1275 head combustion chambers on the exhaust sides and doesn't give as good a line-up of those water gallery ports.

It is prudent to plug the front water gallery transfer port holes and re-drill them using a 1275 head gasket as a template. This is pretty easy even with the engine in the car by tapping the holes then fitting suitably sized grub screws which are then drilled to allow water through in line with the 1275 gasket. Crude but effective and means the block face doesn't need re-surfacing afterwards. If this realignment isn't done, the head gasket is likely to leak water out and down the front of the engine.

If cut-outs are necessary in the block, the easiest way to establish their relative position is to use the 998 head gasket. Place on the block using head studs for alignment. Scribe around the outer exhaust edges of the gasket onto the block surface. Use a fly-cutter of suitable size to machine the cutouts in. It is possible to use a die grinder to make these cutouts, but only in desperation! The depth needs to be sufficient to clear however far passed the head face the exhaust valve will be when the valve is at full lift. To establish this simply subtract the exhaust valve face to head face measurement from the full lift measurement. To be safe I would add 0.040-in./1mm to this depth to ensure no valve to block contact despite using the gasket as a safety margin. And avoid going so deep as to intrude on the top ring land.

Useful part numbers:

C-AEG105 29.5mm competition spec exhaust valve, triple collet groove type
C-AEG106 29.5mm competition spec exhaust valve, single collet groove type
TAM1061 29.2mm standard OE spec exhaust valve, triple collet groove type
CAM4601 29.2mm standard OE spec exhaust valve, single collet groove type.

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by Keith Calver 20. August 2005 09:59

Install engine. It is absolutely imperative that the cooling system is more than sufficient to deal with any temperatures likely to be produced by the engine. More power means more heat to be dissipated. A standard radiator is very unlikely to be able to cope with a reasonable power increase over standard.

Do not fill cooling system yet. Set clutch throw-out and free-play take up. Double-check all connections electrical, oil, fuel and cooling system. Put in engine oil – use a cheap multi-grade mineral oil. DO NOT use either semi or full synthetic oils. They will stop the rings from bedding in. Remove spark plugs, and spin engine over in bursts of a few seconds to pick up oil pressure and prevent starter motor damage. DO NOT start engine until oil pressure picks up.

Once oil pressure is showing, check ignition timing statically. Set to figure advised by distributor maker, or if no figures available, set at around 6-8 degrees BTDC. Re-fit spark plugs and start engine. DO NOT allow to idle under 1,500rpm at start up - 2,000rpm is preferable. Allow engine to run until cylinder head is warm to the touch, then switch off and allow to cool completely. Fill cooling system and re-start. 2,000 rpm should be maintained for the first ten minutes of running, irrespective of use, to prevent cam/follower damage, and help bed same in. After this period, reduce idle to 1,500rpm on race units, 1,200rpm on road units until engine is run in. After this, race units should not be allowed to idle at under 1,200rpm as valve train damage and premature wear can occur from erratic low speed running, and the water pump is very in-efficient at low revs.

Run engine in using part throttle and low loads only, and keep rpm down to no more than 60% of rpm limit. Use the gearbox. DO NOT put engine under unnecessary loads (ie. going up hills in top gear just using the throttle to maintain progress). Although the bulk of the engine requires little running in because of accurate building and tolerances employed, the more miles you can achieve the better the ring seal will be. 500 miles is enough. During running in, make sure the engine does not run hot, too lean or too rich. Both will cause premature piston/ring failure. Temperatures over 95 degrees C (203 degrees F) are unacceptable. If this occurs, re-set static ignition timing to 2 or 3 degrees BTDC, re-check carburettor/fuelling settings, and re-check cooling system capability.

Once the running-in period is complete, re-torque cylinder head nuts – 42lb ft for the nine main 3/8”AF nuts, 25lb ft for 5/16”AF rocker post nuts and end two 3/8”AF nuts if fitted. Re-set valve clearances (see below for settings).

Where roller-tip rockers are used, DO NOT push feeler blades through from front as standard. The roller tip acts like a panel roller and will draw the blade through irrespective of gap size – even if there isn’t one. The feeler blade must be wiped sideways from one side to the other.

Where non-roller tip rockers are used, slacken all lock nuts then as each valve clearance is set screw adjuster in to reduce the valve clearance, gently push feeler blade between rocker and valve stem tip whilst pressing down on the adjuster screw. Now slowly undo screw until feeler blade slides in. Do not force the blade through. When lock nut nipped up the blade should just slide through with a small amount of pressure. If the feeler blade ‘sticks’, clearance is too tight. If it slips through with no resistance, clearance is too loose.

Finally re-check all connections then have the unit set up on a rolling road. As soon as it’s finished, and whilst still hot, ask the rolling road operator to check the ignition timing at, say 2,000 or 2,500 rpm using the TDC pointer/mark on the timing cover/crank pulley. The actual reading is irrelevant, just a reference point. Make a note of this, and check it periodically in the future. It will also serve to re-set it in the event of ignition component changes/engine re-builds for whatever reason in the future. Carry out periodic compression tests – they can help forewarn of possible trouble. Always do them immediately after competitive use or when engine’s hot, with throttle wide open.

Running without an air filter will cause premature wear to valves, guides, seats, pistons and rings.


NOTES: Where engine is used in highly contaminating conditions – i.e. Rally, Rally-X, Grasstrack, etc. - make sure the clutch operating mechanism is stripped, cleaned and re-greased several times a season to avoid clutch slip caused by sized mechanism.



Engine - Reliability

by Keith Calver 20. August 2005 09:57

I've been having quite another chuckle lately at some stuff I've seen in print (and heavily and heatedly discussed by internet) on the subject of 1380cc engines and their professed unreliability. Although I know I have been at pains to explain to folk you don't have to have a 1380cc with very sporty cam profile and so on to have a decent, satisfyingly quick road car - but this reliability problem is absolute hogwash.

Properly built and maintained, these engines will last every bit as long and reliably as any other A-series unit. Ask the likes of Swiftune Racing or MED - they've been churning out 1380cc engines for the masses for years with precious few problems. It's the 'properly built' and 'properly maintained' that are the problems. But then these are the same problems that affect any engine's longevity. Those and selecting an engine specification that best suits your usage and temperament as far as maintenance goes. If you don't want to be regularly involved in maintaining your engine, then go for a spec that will demand less of it. A standard road engine is very, very under-tuned to cope with a severe lack of regular maintenance. A full-bloodied race engine demands near-constant maintenance to keep it alive. Also, don't expect more from the engine than it was built to give - constantly thrashing it to within an inch of its life will do it no good whatsoever if it wasn't built to be able to cope with just that. It is this and the no-or-low maintenance that causes engine builders like the aforementioned problems when punters turn up with 'defective' or destroyed engines - generally the punters fault rather than the engines.
Be sensible about your engine build spec or be fully aware of the consequences of lack of attention. Consider - tuning should always be a compromise between what is possible and what is necessary.

Many are contemplating their forthcoming 2003 racing season, and looking back on their 2002 season. Whilst on the subject of engine reliability, a few words of advice for those drivers who don't want to be forking out for engine re-builds and the disappointment of yet another engine failure/DNF and the soul- destroying loss of money that goes with it.
Generally, a properly built engine will only break when it is forced into doing something for which it was not designed. Components generally only break when forced to endure stresses beyond that which they were designed for. The first scenario is caused by using the engine for braking, the second a feature of engine braking and missed or incorrectly selected gears.
The engine absolutely will not slow the car down any faster or as efficiently as the brakes. The brakes are designed for slowing the car down; the engine is designed to make it go. And in the act of attempting to use the engine to slow the car, missed gears are easily achieved. Both situations cause a massive increase in loads and stresses the engine components have to deal with. It is this acceleration on the acceleration (acceleration squared) that causes engine parts to go 'ping'. To avoid unnecessary expense, don't get the two mixed up.

Oh - and whilst on the subject of engine reliability when racing and 1380cc engine unreliability - I've just stripped and checked my mate's 1380cc Sprite engine having done no more than a strip/inspection a couple of years back.
Apart from a cam change two years ago following a broken cam follower (defective follower) along with a new set of crank bearings, a recently broken rocker shaft (no real conclusion found) and a 'latest development' cylinder head at the same time, the basic short block assembly has now done 5 years racing. And I mean racing as in European racing where the engines do probably three to four times the racing mileage of a UK car. The cam fitted two years back has a very 'savage' profile since there's a new rev limit was introduced - bigger power at lower rpm being the goal, I think the result was a fine 140bhp at 7,000rpm at the crank.
Testament to a driver being mechanically sympathetic but still competitive, the outstanding protection proffered by Torco oil, and a half-decent engine build (a-hem) is the fact that all it really needs is a new timing chain and a set of piston rings (number 4 cylinder runs a bit hot in these arse-about-face engined cars so a change is prudent). Oh - and a set of new main cap dowels coz I'm not happy with the fit of those in there now. Everything else is perfect and will be re-fitted.
Just goes to show how reliable a 1380cc engine with serious performance can be when built to a specification suitable for it's intended use and looked after properly.



Engine - Metro engine identification data

by Keith Calver 20. August 2005 09:55

The widespread and prolific fitment of Metro engines into Minis - usually those endowed as standard with small-bore (850/998/1098) engines - practiced in the UK has been spreading to many other countries worldwide.

So it's not surprising that the most commonly asked question has also become more prolific concerning the fitment of said engine - apart from actually how to manage the transplant and the differences in the installations, covered in articles relevant article on this site - is just which type of engine the individual concerned has bought or what they already have fitted to their car and is it worth keeping or junking. One initial question I pose often draws a pregnant silence whilst said inquiree scrambles their brains trying to find an answer for. Following that protracted pause, 'I dunno' is the usual answer. I then have to get into a lengthy explanation as to how to determine what said engine is. To circumvent as many of these instances as possible, and endow all and sundry with the wherewithal to do the detective work for themselves, I have here produced the most comprehensive listing of engine identification data for the Metro A+ engines I could unearth given a reasonable amount of time. There should be enough here for everybody to make a very fair identification of what they have and what they're looking for. The number you will need is that stamped into an aluminium plate riveted to the engine block just below the thermostat housing.

A word of warning - whilst the data given here is as accurate and complete as I could make it without 6 months-worth of hermit-like investigation, there are bound to be oddities. Austin/Morris, BL/Austin Rover Group/Rover were never dedicated at keeping 100% correct records, particularly post 1970 - that's why Heritage really struggle with trying to identify cars manufactured after 1969. The Metro data - or lack of it - proves the point. It's nothing like as comprehensive as the Mini stuff.

Whilst most of the engines do not really give a whole lot of difference in performance, the one outstanding version is the MG Metro engine. Where the majority of the variously similar power plants put out around 63-65bhp, the MG metro achieves a more spirited 70-74bhp. This is due to a higher compression ratio (10 -1), larger inlet valve (35.7mm instead of 33.3mm), and - mainly - a more sporty camshaft with half-decent induction and exhaust systems. The inlet manifold being a reasonably good flowing, water heated aluminium example. Rover finally got the hint having witnessed the prolific after-market fitment or such an item to Minis in epic proportions for years. The exhaust manifold is a cast iron 'LCB' style with a pair of exhaust downpipes instead of the more common single item and works very efficiently. A bonus of this over the more common after-market steel-tubed LCBs is that it is much quieter by dint of absorbing more exhaust 'noise'. Coupled to a pair of Maniflow tubular steel downpipes it is very nearly as efficient as a full tubular steel manifold. The cylinder head is more along the lines of the old Cooper S spec and in fact flows slightly more air than it's predecessor, the camshaft being the sportiest fitted to any production A-series engine. It uses the inlet profile and timing of the original 997 Cooper cam and the exhaust specification of the old Leyland Special Tuning '731' fast road cam.

1st prefix group identifies engine capacity -
85 = 850cc (mainly used in export only models)
99 = 998cc
12 = 1275cc
1st prefix letter identifies engine orientation -
H = Transverse

2nd prefix group identifies gearbox, ancillary and specific engine type -
prefix number identifies general engine installation details (i.e. '907')
prefix letter identifies emissions equipment type (i.e. 'P')

3rd prefix group identifies compression ratio and serial number
prefix letter denotes compression ratio -
H = High compression
L = Low compression

Prefix number is engine serial number (i.e. 101, 102, etc.)


2nd prefix number combination references
897 - Yd + Bf + Hm + Zj +Sk
898 - Yd + Bf + Hm + Zj + Tj
907 - Yd + Bf + Hm + Sk
908 - Yd + Bf + Hm + Tj
929 - Yd + Bf + Hm + Dn + Sk
951 - Yd + Bf + Hm + Zj + Dn + Sk
955 - Yd + Bf + Hm + Nl + Sk
958 - Yd + Bf + Hm + Nn + Sk
959 - Gd + Bf + Hm + Fp + Sk
962 - Yd + Bf + Hm + Hf + Sk
963 - Yd + Bf + Hm + Hf + Zj + Sk
977 - Yd + Bf + Hm + Xc + Jn + Sk
978 - Yd + Bf + Hm + Xc + Dn + Sk
996 - Yd + Bf + Yn + Sk
A02 - Yd + Bf + Hm + Nn + Sk
A05 - Yd + Bf + Hm + Hf + Zj + Kp + Sk
A06 - Yd + Bf + Hm + Kp + Sk
A07 - Yd + Bf + Hm + Zj + Lp + Sk
A08 - Yd + Bf + Hm + Lp + Sk
A09 - Yd + Bf + Hm + Nl + Lp + Sk
A47 - Yd + Bf + Hm + Vn + Sk


2nd prefix letter reference details
Bf - Alternator with negative earth
Dn - Base line engine with single outlet exhaust manifold
Fp - Metro high performance derivative (meant to identify high compression, sportier than
original and initial standard cam and can include MG Metro specification derivatives)
Gp - High pressure electric fuel pump (therefore MG Metro Turbo)
Hf - 1st alternative compression ratio (should be 9.7-1CR as used in early pre 1983 range)
Hm - LC8 design variant (probably means the 'Low Compression' A+ derivative of the A-series
engine - as in '&' denotes a Mini engine)
Jn - 1980 requirements (probably closed circuit breathing and lean-running)
Kp - 3.65 Final Drive fitted to gearbox
Lp - 3.105 Final Drive fitted to gearbox
Nl - Hot climate specification (usually more conservative ignition advance curve in dizzy,
different thermostat and different fuelling, i.e. carb needle)
Nn - Alternative compression ratio (should be 9.75-1CR as used in post 1983 general range)
Sk - Standard ratio gearbox with 3.44 Final Drive, inboard CV joints and rod change
Tj - Automatic gearbox fitment
Vr - Post Office spec - i.e. low compression and low final drive
Yc - Police spec - i.e. high compression, probably MG cam and up-rated diff pin
Yd - Mechanical fuel pump
Yn - MG Metro design/specification variants (high CR, sportier CAM6648 cam, bigger inlet
valve in head) also known to be fitted to LHD Van Den Plas
Zj - Cold country spec (more advanced advance curve in dizzy, different thermostat and so on)

2nd prefix letter data
AA - Carburetter crankcase ventilation and intake air temperature control
P - Carburetter crankcase and clean air package



99 - 998cc
H - Transverse
907 - Yd + Bf + Hm + Sk
Yd - Mechanical fuel pump
Bf - Alternator with negative earth
Hm - LC8 variant - A+ Metro engine
Sk - Standard gearbox ratios with 3.44 final drive, inboard CV joints, rod change
P - Carburetter crankcase and clean air package
H - High compression
101 - Engine serial number



Engine - Identification data

by Keith Calver 20. August 2005 09:51

If you have the engine tag still attached to the engine - just in front/below the thermostat housing - or perhaps the original engine number in the log book then the following should help you determine which engine you have. For Metro units, see 'Engine - Metro identification data'.

Original engine identification numbers

8A Austin up to 25000
8MB Morris up to 25000
8AM Austin & Morris 25000 onwards
8AH Austin & Morris Automatic
8AJ Austin & Morris closed circuit breathing
8AK Austin & Morris automatic with closed circuit breathing
8WR Wolseley Hornet & Riley Elf
8AC Moke
85H/101 All variants 1969 onwards

Note: third suffix letter denotes compression type, L = Low, H = High, e.g. 8AM/U/H101 denotes high compression.

9WR Wolseley Hornet & Riley Elf Mk2, pre closed circuit breathing
9AD Austin, Wolseley Hornet & Riley Elf Mk2 with remote type gearbox and closed
circuit breathing
9AE Wolseley Hornet & Riley Elf Mk3
99H/-/101 on Wolseley, Riley, Mini 1000, Clubman1000 1970 onwards and Mk3 with dished
99H/791 Mini 1974 onwards with dished piston
99H/997 1980 onwards A+ block, flat top psitons, economy fitment with 2.95 final drive
99H/A97P A+ block with dished pistons, pre-A+ gears, 3.44 final drive & 12-inch wheels

998 A+ block with centre locating tang in main cap, 1985 onwards
Flat top piston with circlip wrist pin retention
99H/B81 Up to engine number 127431
99H/C20 Up to engine number 105023
99H/997 From engine number 127422 with 2.95 final drive

Flat top piston with press fit wrist pin
99H/B81 From engine number 127432
99H/C20 From engine number 105024

Flat top pistons with press fit wrist pins, Lead-free cylinder head
99H/G30 or G32 or G33
99H/F15 or F16
99H/E20 or E21

Dished pistons with circlip wrist pin retention
99H/B83P Up to engine number 102908
99H/B84P Up to engine number 100216

Dished pistons with press fit wrist pin
99H/B83P From engine number 102909
99H/B84P From engine number 100217

Dished pistons with press fit wrist pin, Lead-free

1100cc (1098cc)
10AMW/Ta Clubman Estate and Austin 110 (ADO16 shape)
10H791 Clubman saloon
10H/-/H All Austin 1100 2 & 4 door derivative Saloons (ADO16 shape)
10GR/Ta/H MG1100 (ADO16 shape)
10GRB/Ta/H MG1100 & Wolseley 1100 (ADO16)
10V/Ta/H Vanden Plas 1100 (ADO16 shape)

997 Cooper
9F/Sa/H101 to 2637 except 19201 to 20410 (became 1070S)

998 Cooper January 1964 onwards)
9FA/Sa/H Mk1 Austin pre closed circuit breathing
9FD/Sa/H Mk1 Morris up to engine number 1934, all Austin Mk2 closed circuit breathing and
Morris Mk2 from engine number 1935-33660 with closed circuit breathing
9FD/Xe/H 4 syncro gearbox introduced
99/-/H Last of manufacture 1969

Cooper S variants
9F/Sa/X Engine numbers 29001-29003 with Tecalamit filter
9FD/Sa/X Closed circuit breathing introduced with Tecalamit filter
9FE/Sa/X Closed circuit breathing, oil filter with oil light switch introduced
9F/Sa/X Engine numbers 29039-30029 Purolator oil filter with oil light switch and closed
circuit breathing
9F/Sa/H Engine numbers 26501 to 33660 and 19201 to 20410
9FD/Sa/H Engine numbers 33661 to 33948 with closed circuit breathing and oil light switch in
oil filter head
9F/Sa/Y Engine numbers 31001 to 31504 pre closed circuit breathing with Purolator oil filter
9FD/Sa/Y Closed circuit breathing with oil light switch on filter housing after engine number
9FE/Sa/Y Closed circuit breathing with oil light switch on Purolator filter housing and piston
design change
9F/Sa/Y From engine number 32378 onwards, cosed circuit breathing with Purolator filter
with oil light switch, Aeg510 camshaft introduced at engine number 40006, cross-
drilled EN40Bcrank at engine number 42730 and metal dipstick tube at engine
number 42548 onwards
12H397 Cooper S Mk3 with dynamo, negative earth and Tuiftrided EN16T crankshaft
12H398 Cooper S Mk3 with alternator, negative earth and Tuftrided EN16T crankshaft

Note: Only Cooper S engines with prefix '9F' had EN40B forged steel, nitrided crankshafts. All other A-series engines had EN16T steel crankshafts which were only Tuftrided on Mk3 'S' and Austin 1300GT (ADO16) and were stamped 12G1683.

1275cc, Solid wall block (no tappet chest covers)
12G/Ta/H ADO17 shape Wolseley, Riley, MG & Vanden Plas fitted with S rods
12H379 1275GT with dynamo, negative earth, electric fuel pump and remote type
12H380 1275GT with alternator, negative earth, electric fuel pump and remote type

12H389 1275GT with dynamo, negative earth, mechanical fuel pump and remote type
12H390 1275GT with alternator, negative earth, mechanical fuel pump and remote type
12H706 1275GT with alternator, negative earth, mechanical fuel pump and rod change
12H397 Cooper S Mk3 with dynamo and negative earth
12H398 Cooper S Mk3 with alternator and negative earth
12H/-/ 1275 Austin ADO16 & Allegro
12H610/635 Innocenti Mini with duplex cam drive gears and 11-stud head
12H719/832 Innocenti Mini with simplex cam drive gears and 11-stud head

1275cc, 1990 onwards (12A numbers)
12A/2A Carburrettor type
12A/2B Carburrettor and catalyst type
12A/2D SPi (Single Point injection - Tbi, throttle body injection) with 9.4-1 CR
12A/E SPi (Tbi - throttle body injection) with 10-1 CR
With the following suffixes:
F53 10.0-1CR, 3.105 final drive, catalyst, oil cooler
F75 9.4-1CR, SPi, 3.105 final drive, closed loop catalyst
F76 9.4-1CR, automatic with closed loop catalyst
F77 10.0-1CR, SPi Cooper, 3.2 final drive, closed loop catalyst
G01 10.0-1CR, 3.105 final drive, catalyst, no oil cooler
G03 9.4-1CR, 3.105 final drive, catalyst, May 1992 onwards
G04 9.4CR, 2.76 final drive, catalyst, French only spec
G05 9.4-1CR, automatic with catalyst

Factory replacement engine reference numbers (i.e. New, and Gold and Silver Seal units)
8G28 850cc - Oil feed to primary gear type crank with 1.375-inch tail shaft
8G35 850cc - Deva bush conversion type crankshaft with 1.375-inch tail shaft
8G45 850cc - Gold Seal, 1.5-inch self oiling primary gear/crankshaft type
GSE1101E 850cc - Gold Seal unit
RKM1101E 850cc - Silver Seal unit
BHM1307E 850cc - Gold Seal unit, 85H prefix replacement
8G18 997cc Cooper - Oil feed to primary gear type crankshaft
8G29 997cc Cooper - Deva bush type primary gear and crankshaft
8G36 997cc Cooper - Oil feed converted primary gear and crankshaft
8G33 998cc Cooper - Fitted with 28G193 (12G202) cylinder head
8G40 998cc Cooper - 28G222 (12G295)cylinder head introduced
8G42 998cc Cooper - Closed circuit breathing rocker cover and side plates
8G49 998cc Cooper - Purolator oil filter with oil light switch introduced
GSE1103E 998cc Cooper - Gold Seal unit, was RKM1120E Silver Seal
RKM1103E 998cc Cooper - Silver Seal unit
8G57 998cc - New from 1969 and exchange for all pre-A+ up to 1981
GSE1102E 998cc -Gold Seal unit, was RKM1119E Silver Seal unit, pre-A+ up to 1981
RKM1102E 998cc - Silver Seal unit, pre-A+ up to 1981
RKM1119E 998cc - Silver Seal unit, replaced by RKM1102E, pre-A+ up to 1981
BHM1232 998cc - Low compression dished piston, CAM6267 camshaft, early cylinder head
and crankshaft main bearings with side locator tang, A+
BHM1377 998cc - High compression flat top piston, CAM4717 camshaft, early cylinder head
and crankshaft main bearings with side locator tang, A+
BHM1458 998cc - Low compression piston, CAM6267 camshaft, late A+ cylinder head and
crankshaft main bearings with central locator tang, A+
BHM1460 998cc - High compression press-fit wrist pin piston, CAM4717 camshaft, late A+
cylinder head and crankshaft main bearings with central locator tang, A+
LBB10089 998cc - Low compression press-fit wrist pin piston, CAM6267 camshaft, lead -
free late A+ cylinder head and crankshaft main bearings with central
locator tang, A+
8G156E 1100cc - Clubman, Special and Austin 1100 (ADO16)
RKM1150E 1100cc - Silver Seal unit for Clubman and Special
RKM1151E 1100cc - Silver Seal unit for Clubman and Special
BHM1042 1100cc - New and Gold Seal units for Clubman and Special, 1974-1980
BHM1229 1100cc - New and Gold Seal units for Clubman and Special, A+ Block, 1980 on
8G38 970cc - Gold Seal unit, pre closed circuit breathing, Cooper S
8G41 970cc - Gold Seal unit with closed circuit breathing sideplates, Cooper S
8G46 970cc - Gold Seal unit withoil light switch in filter housing, Cooper S
8G133 1070cc - Gold Seal unit, pre closed circuit breathing, Cooper S
8G153 1070cc - Gold Seal unit with closed circuit breathing side plates, Cooper S
8G145 1275cc - Pre closed circuit breathing unit, Cooper S
8G154 1275cc - Closed circuit breathing side plates unit, Cooper S
8G155 1275cc - Oil filter housing with oil pressure light switch, Cooper S
8G174 1275cc - Fitted with AEG510 camshaft, Cooper S
38G464 1275cc - Introduced in 1970, most of which were fitted with EN16 Tuftrided
8G200 1275cc - New and Gold Seal units Clubman 1275GT
38G527 1275cc - New and Gold Seal units for engine numbers prefixed 12H706, 12H707 &
12H831 for Clubman 1275GT
RKM1130E 1275cc - Silver seal unit, was RKM1112E, for Clubman 1275GT, pre-A+
RKM1152E 1275cc - Silver Seal unit for Clubman 1275GT, pre-A+
RKM1112E 1275cc - Silver Seal unit for Clubman 1275GT, pre-A+
BHM1220 1275cc - A+ unit for Clubman 1275GT
8G199E 1275cc - Gold Seal unit with Duplex cam drive gears for 1300GT (ADO16) and
Innocenti 1300, 11-stud cylinder head
38G559E 1275cc - Gold Seal unit with Simplex cam drive gears for engine numbers prefixed
12H719 and 12H832, for 1300GT (ADO16) and Innocenti 1300, 11-stud
cylinder head
GSE1109E 1275cc - Gold Seal unit for 1300GT (ADO16) and Innocenti 1300, 11-stud cylinder
RKM1133E 1275cc - Silver Seal unit for 1300GT (ADO16) and Innocenti 1300, 11-stud
cylinder head
BHM1209E 1275cc - Gold Seal unit, replaced all Innocenti 1300 engines from engine numbers
prefixed 12H610, 12H635 and 12H832

All engines pre-fixed with 'GSE' or 'RKM' were of UNIPART origin when BL split its parts organisation.

'E' at the end of a part number denotes it is a reconditioned, service unit only (basic engine assembly with no ancillaries).

'N' at the end of a part number denotes a brand new unit.



Engine - 1275, 95bhp sports/tourer test result

by Keith Calver 20. August 2005 09:27

DIY enthusiasts often believe that building an engine to give excellent all-round road performance is beyond them. Mainly from comparisons made between what they have been able to achieve and what specialists say should be achievable from any particular type of engine build.

Generally scrambled further by the non-perfect match of parts and components used between aforementioned specialist and erstwhile DIY-er, and the ritual 'nose-tapping and knowing winks' display of those specialists. Something you can very nearly 'see' even when talking to such folk on the phone - or that inimitable 'ah, yes, well…' So some form of 'black art' is implied. Whilst there is most definitely a degree of 'feel' involved between the real specialist's results and those of just a good engineer - the bones of the deal is subject to no such thing and is certainly within the capability of the DIY enthusiast given the necessary information. And that has been the problem. Despite a true plethora of books written on the subjects of blueprinting and tuning of all manner of engines (i.e. 4, 6, 8, 12 cylinder and so on) not all of it is relevant to our wonderful, archaic A-series and not easily transposed by the DIY-er. What is needed is very specific information appertaining to our unique A-series engine.

To supplement this, it would be even better if this would encompass a very specific engine build as far as all components used and for a specific application. Daunting if you consider the myriad of cam/head/carb choices voiced by the multitudes of A-series meddlers (not at all meant in a derogatory way, as I include me in that description) used over the years. Of which there are roughly four 'camps' - the 'good old boys' from the Mini's inception, the 'young whipper-snappers' of more modern technology, the 'liberals' using a bit of both and lastly the 'T-BASE' brigade (those that have read and re-read David Vizard's 'bible' on A-series tuning so that they can quote chapter and verse, strangely enough encumbered 'Tuning BL's A-Series' - hence T-BASE).

Fortunately this whole tuning deal has gone round very nearly full circle and has tried just about every combination possible with whatever modern technology was suggesting was 'the way to go' at the time. And some very talented and clever folk have given more than their two-penny-worth into the bargain. What that has given us is a vast reduction in the prolific list of possible components to make an engine suitable to our needs. Particularly where modern road/street performance is concerned. The main criteria being an engine that idles smoothly, has exemplary emissions levels, pulls strongly from low rpm, will give rapid overtaking performance yet be fun all the way to the useable (sane/sensible?) redline when the situation presents itself.

It was to this end that I carried out the 1275 engine build detailed in the relevant articles, and to prove that having to go out to 73.5mm bore (1380) isn't an absolute necessity to have a blistering street performer.

So given a straight forward engine build with proper detailing and 'off the shelf' components list consisting Swiftune SW5 camshaft, Min Tec 'road rocket' type head (as supplied by Mini Spares/Mania), 10.4:1 compression ratio, standard crank, A+ rods, Mini Spares/Mania 'Mega' piston set +0.040", lightened duplex gear set, single 1.75" HIF SU, Mini Spares intake manifold, Maniflow medium bore LCB, RC40 exhaust system, K&N cone-type air filter, 1.5 roller-tip rockers and Aldon Yellow non-vac dizzy, along with the other necessary engine build components what kind of performance is easily attainable?

The first rolling road visit was a disaster as far as I was concerned. When running the engine in it felt terrifically strong. After 400 miles it went on the rollers. The result simply wasn't what I expected - a measly 78bhp at the crank. I had come to expect around 92-95bhp from engine dyno tests. The dizzy wasn't giving the figures it should and was making set-up difficult. So the testing was aborted. I started to think there was something else to blame. Once home I checked everything from the tyre contact patch to the carb mouth and everything in-between - tracking, camber, wheel bearing drag, brake drag, gearbox drag, cam timing, sorted the dizzy advance/ignition timing problems (not deemed to be causing the massive deficit in power), valve/cam timing, valve/lash clearances, valves sticking in guides, compression test, leak-down test, manifold air leaks, carb condition, fuel supply, everything. Absolutely nothing suggested anything was wrong anywhere. And that is very annoying since at least if a reason is found it solves the problem and takes away the doubts.

Then I started to suspect the exhaust system since manufacturing techniques had altered somewhat from the original RC40 systems. I decided to run a test on exhausts as part of the re-rolling road test to check on this (see 'Exhausts - Millennium and others tested'). But even this wasn't really conclusive in my mind. Then I remembered my notes when building the engine and went back to them - concerning the 'Mega' pistons. I had commented on how tight the engine felt when the short motor assembly was checked. Removing the pistons/rods and re-building/re-testing with the rings removed one type at a time until only the oil control rings were left I found the oil control rings were the cause of the increased tightness I was getting. I decided to re-run the rolling road test with the rings as is and just do the exhaust swap to see what gave there and deal with the rings if there was still a major power deficit.

Back on the rolling road with only the dizzy vac unit removed and re-timed as Aldon suggest and 1,000 miles on the clock, the first run was done with the mixture as it was last time. And bingo! - the missing power was there immediately! The mixture was leaning out slightly at the top end, so a needle change was made and a re-run done. The ignition wasn't changed any from where I set it - at 28 degrees max advance proving very efficient combustion. The conclusion was that the Mega oil control rings take a good few miles to settle themselves in (see 'Pistons - Mega ring performance').

The results were astounding:

Road speedRpmBHPTorque
30 2,800 54.1 89.54
40 3,700 67.0 95.10
50 4,600 80.1 91.45
60 5,400 90.3 87.82
70 6,300 92.0 76.69
80 7,200 87.00 63.46

Emissions at idle were 3.5% CO, and only a mere 697 HC!! Where 1200 HC is a vehicle test pass!

I can't tell you how much fun this made the car to drive. It is blisteringly quick for general road use, has so much urge that over-taking is a cinch, and would definitely benefit from a final drive change to a 3.1. With the 3.44 currently fitted you get in to top gear and then just press the go-pedal no matter what road speed you're at! Incidentally the tests were all done in third gear to assimilate more closely road driving. It's not as hard on the car or rolling road either. These figures are almost identical to those gained from dyno sessions on this type of engine build - so the exhaust wasn't the problem at all.

These figures are real, no bullshit, achievable results from simply following the engine build articles and components usage. Sure, a 1380 will be even better - but not by that much. The dyno results suggest only a few more horsepower and barely a handful foot-pounds more torque. Going the +0.040" over-bore route you will still have at least two re-bores to go on that precious block!

Useful part numbers:
C-AHT135 Min Tec 'road-rocket' type cylinder head pre-92 - has by-pass hose
and heater tap take-off - standard spec components
C-HT136 Min Tec 'road-rocket' type cylinder head for twin point injection only
- standard spec components
MSE3 Min Tec 'road-rocket' type cylinder head pre-92 - has by-pass hose
and heater tap take-off - race spec components
MSE4 Min Tec 'road-rocket' type cylinder head post-92 - has no by-pass hose
and no heater tap take-off but not for twin point injection - race spec
MSE7 Min Tec 'road-rocket' type cylinder head has no by-pass hose
and no heater tap take-off for twin point injection - race spec
C-AJJ3378-40 Mega piston set +0.040"
C-AHT446 1.5 ratio roller-tip rockers
C-AJJ3325 Ultra-light steel duplex kit
Aldon Y Aldon 'Yellow' dizzy, non-vac, pre A+
Aldon Y+ Aldon 'Yellow' dizzy, non-vac, A+
WKN1 OSET 1 degree offset cam key
WKN2 OSET 2 degree offset cam key
WKN3 OSET 3 degree offset cam key
WKN4 OSET 4 degree offset cam key
WKN5 OSET 5 degree offset cam key
WKN6 OSET 6 degree offset cam key
WKN7 OSET 7 degree offset cam key
WKN8 OSET 8 degree offset cam key
WKN9 OSET 9 degree offset cam key
C-AHT770A 1.75" SU intake manifold
C-AEG365 Maniflow medium bore LCB
RC40 Original RC40 exhaust system
RC40FK Exhaust hanger kit comprising all rubber mounts and hangers
56-9327 K&N cone filter for HS6 1.75" SU
56- 9330 K&N cone filter for HIF 1.75" SU
SDCLEANER K&N air filter cleaner
DOIL K&N air filter oil



Engine - 998 tuning, further options

by Keith Calver 20. August 2005 07:36

Following on from the easily bolted on performance enhancing components out-lined in the stage one section, we need to consider where to go to get more power output.

MSC/MM - Mini Spares Centre/Mini Mania
BBU - Big Bore Unit (refers to all 1275cc-based units)
SBU - Small Bore Unit (refers to all sub-1275cc units, here the 998)
BHP - Brake Horse Power
CR - Compression Ratio

To improve engine out-put, you need to increase the engine's 'breathing' ability. The stage one kit deals with all the easily bolted-on external parts, and represents the best increase for investment. From here on in the power increases will cost commensurately more money. Power production of any engine, once the 'breathing apparatus' (induction/exhaust system) has been dealt with to cause no restriction - or certainly minimised where use of relatively standard major components such as the carb is concerned - is down to the cylinder head and camshaft. Both play a vital role in improving the engine's ability to breathe. The head through improved airflow by way of modification or replacement, the cam through increased valve-opening periods. How far these modifications and changes should go are dependant on what the engine is to be used for, or the power output required.

Books have been written on these subjects; here we're dealing with sensibly priced options for reasonable gain in engines that are used every day. Waxing lyrical about the virtues of this or that cam, and so-and-so's or such-and-such's cylinder heads are all well and good - but mean nothing without hard, practical proof. Consequently the following will be based on recent tests carried out by me to assess such changes.

Cylinder head.
After the stage one kit, this is the next easiest option as far as fitment goes. It's almost a 'bolt-on' part, but is a little more involved and a little more costly so is moved up a category.

The standard cylinder head is pretty restrictive where bigger power outputs are the main aim. To make appreciable gains it needs a fair amount of work done. Simply carrying out 'stage one' port, chamber and polish mods really don't do much at all for your money. The only sensible option is a standard head modified to 'stage three' spec, or a 12G295/12G206 Cooper head. Using a BBU 12G940 casting is an option - but not terribly practical (see 'Engine - 998 tuning, fitting a 1275 head').

The much coveted 12G295/12G206 heads are all-but non-existent realistically now. There are some about - most have been well used and abused, many cracked or modified into uselessness, with just a few, rare, un-molested examples of the species. But even a good example is likely to need complete refurbishment, particularly for the modern world where unleaded fuel is to be used. Suitable exhaust valve seat inserts will need fitting, new guides, seats re-cut, probably new valves, valve stem seals, and in all probability new valve springs. And then there's the machine-work needed to get it to work on your 998 - hefty re-facing to get CR to a sensible level since the standard head has a capacity of 24.2cc, the Cooper heads 28.4cc. That's a chunk to remove; charged by the cut it'll cost plenty. And having gone through all that - reliability is a problem - they're prone to cracking.

That leaves us with the 'stage three' spec modified standard head. MSC/MM sell heads modified by myself (Min Tec). The valve sizing is as that of the Cooper heads with all necessary port and chamber work carried out to give the best flow gains available within limiting criteria and inserted for unleaded fuel use. The main limitation is the combustion chamber - modifications are kept within sensible bounds so suitable chamber size is obtainable without excessive cost. To improve the chamber beyond that used would require large amounts of material to be removed off the head face. This generally breaks in to the rocker gear oil feed gallery necessitating this be brazed up, re-routed, and re-faced to true. The small improvement available simply doesn't warrant the extra costs incurred to do this. Even so, flow testing (results below) has shown that this style of stage three head all-but matches the inlet flow of the Cooper head, with better exhaust flow results so offers directly comparable performance, are available 'off the shelf', and are far, far more reliable. Particularly when comparing the figures below 0.350" lift as the cam/rocker combinations used only reach 0.340" lift.

LIFT (in)
12G295 HEAD
0.050 16.7 16.0 19.7 18.3 17.9 16.0
0.100 32.5 27.1 36.4 35.3 38.2 29.7
0.150 42.6 38.1 51.1 49.6 51.4 41.9
0.200 50.2 47.0 62.8 57.2 65.2 52.5
0.250 55.8 51.4 71.4 61.4 73.5 57.2
0.300 60.4 54.6 78.9 64.5 81.1 61.0
0.350 63.8 56.9 84.3 66.8 87.0 63.6
0.400 65.3 58.9 88.9 68.9 91.8 65.1

Superflow 600 fully computerized flow bench. Tested at 25-in of water.
Flow test readings are average of all ports tested on one of each cylinder head types.

Off the mark, a camshaft change to something more suitable will give you more 'bang for your buck' compared to a cylinder head. Having said that, it will not give initially as much power with the standard head as a stage three head will with a standard cam.

There is a multitude of camshaft options available, and most of them will have been tried by some one, somewhere. The problem is, many of them will have been tried in combinations that really didn't suit them - be this the wrong combination of parts, or used for the wrong application. It's no good fitting a camshaft that doesn’t start working until 5,000rpm shows on the tacho when you spend almost all your time driving in traffic. Likewise, a mild road cam isn't the best option for a circuit racer. Unfortunately, too many folk get lead down the wrong path here, and end up with a completely unsuitable cam for their particular situation. No more so than where road use is concerned.

I've run the gambit on just about every size of Mini engine in almost every possible situation along with a huge variety of camshafts. One thing stands tall above all the others - I have nearly always gone back to a relatively mild profile for roadwork. Something that gives it's best between 1,500-5,500rpm almost irrespective of engine size. The reason being this is where you tend to spend most of your time when driving on the road. Needing to run much over this means you either have an unsuitable final drive ratio, or just use the engine for scaring the local community at the weekend.

Considering the engine size and the operating range, this really does cut down camshaft choice to something in the 'mild' as opposed to 'wild' area. In my book the 997 Cooper profile takes some beating and would be my first recommendation to anybody wanting a decent road-burner. Or did until a few months ago - but more of that in a moment. It gives the right spread of power without being fussy or peaky. And the gain is pretty impressive over the standard item in an otherwise completely standard engine. Not only that, but it will idle smoothly and quietly and give emissions passing CO and HC readings. Something many of the 'modern' breeds of camshafts simply can't do without much frigging and fudging. With this in mind it was my first choice for the test I recently carried out for Mini Magazine where the criteria given matched almost exactly the aforementioned points.

Unfortunately I'd already built and installed the engine before I got my hands on one of Swiftune Racing's SW5 cams. This is the one I really would have liked to test, as it is something new that has been giving unbelievable results in practically all engines it's been tried in. I'm not allowed to give out specific details, what I can say is it is a 'modern' version of the 997 Cooper cam - which goes to prove that the old profile was pretty good in the first place and hard to beat by later 'developments'.

Rocker Gear.
It's pretty widely known that high-lift rockers don't give good results on 998s. The standard rocker gear, however, is a little short on what's required. Despite being 'accepted' as giving 1.25:1 ratio, they don't. You'd be lucky if the pressed steel versions give 1.23:1, and wildly lucky if the later sintered type gave 1.22:1 (they generally only manage a paltry 1.21:1). The 998 needs around 0.340" valve lift to make good use of the head mods - but not much more. The 997 camshaft has a lobe lift of 0.263". To get the required lift means rockers with a real lift ratio of 1.3:1 are needed, so I used the MSC/MM 1.3 roller-tip versions for the SBU. These give the required lift within a few thou.

As a footnote to this section, using the SW5 camshaft means sticking to the standard rockers as it develops more lift at the lobe.

Power Gains.
So what do we get after all our deliberation and hard work? The tests were carried out on the same rolling road I use for all my testing now that I live in the 'northern wilds' - GRV at Littleborough, home of the British Vita Racing Cooper Ss run by Harry Ratcliffe and Geoff Goodliffe (the 'G' & 'R' in the title). The exception was the stage one kitted Mini with a stage three head fitted. This was done by a good friend of mine, Steve Harris (ex-Downton man and well known Mini engine builder). But this doesn't matter over-much as actual bhp readings are not what we're looking for, as they are meaningless considering standard power outputs vary so much. It's the percentage we're interested in for comparative purposes.

A good, low compression 998 gives 30bhp. A good stage one kit (mod1) boosts this to 36bhp. The 997 Cooper camshaft and standard head (mod2) gave 42bhp and the 997 Cooper camshaft/stage three head/1.3 roller-tip rockers combination (mod4) gave 48BHP. Using percentages is a more relevant way of comparing results from different sources, so converting the aforementioned we get the mod1 kitted motor giving 20% more, mod2 giving a 40% increase over standard, and mod4 giving a whopping 60% over standard! Add into this equation the 43% increase that Steve Harris got by adding a stage 3 head to the stage one kit (mod3) on a standard engine and we've a full house of results -

Percentage power increase with each step:
Stage one kit +20%
Standard engine plus 997 Cooper cam +40%
Stage one kit plus Stage 3 head +43%
Stage one kit plus 997 Cooper cam, stage 3 head and 1.3 rockers +60%

A 60% increase is mighty impressive - especially when you consider it still idles sweetly, gives very low CO and HC readings at idle without any MOT/vehicle testing 'fore-play', and actually gives more miles per gallon than standard! I largely suspect the Swiftune SW5 cam would give a few more bhp, but more importantly an increase in the over-all torque out-put - the most important factor for a street unit.

Useful part numbers:
C-AHT88 Stage three, unleaded SBU cylinder head assembly
C-AEG588 1.218" diameter nitrocarborised EN214N inlet valve
C-AEG589 1.040" diameter nitrocarborised EN214N exhaust valve
C-AJJ4037 Manganese-bronze valve guide - set of 8
C-AEA526 Dual valve spring set - 180lb
TAM2068[ Lead-free exhaust valve seat inserts
ADU4905 Stem seals - latest top-hat/sprung type
GUG702506HG SBU genuine Rover head gasket
KC567M A+-drive type 997 Cooper profile camshaft
KC948 Pin drive type pp7 Cooper profile camshaft
C-AHT405 1.3 ratio roller-tip rockers, SBU only
AJM601 Exhaust manifold gasket
GUG705009VC Rocker cover gasket
TG101 Thermostat housing gasket
88G221 Heater tap gasket