FULLY-FLOATING PRIMARY GEAR BUSH

Countless Mini enthusiasts have been dogged by primary gear bush hassles on 1275-based engines - in particular the one nearest the block (the front one). Worn ones are expensive and difficult to replace for the DIY-er because they need machining to the correct size, a job that needs to be done very accurately - a particular problem for over-seas enthusiasts.

Primary Gear - Bush Replacement

With the cost of new primary gears spiralling ever upwards, and the availability of good, serviceable used ones, fitting new bushes to existing gears is becoming a more common solution. For some reasons for bush failures and rectification to stop it re-occurring, see article Primary gear - Bush problems. Since there is no useful information given in any of the workshop or DIY manuals on this subject, following is my approach to dealing with the issue. The first thing to get to grips with is which bush is which. This has added an element of confusion to many conversations I have had with folks on this subject, so - the FRONT bush is the one nearest the engine block, the REAR bush is the top-hat one nearest the flywheel. This is because the front of the engine is actually the radiator end - quoted in 'in-line' engine-speak. The REAR bush is the same on all primary gears - be they for small or large bore engines. The FRONT bush is different for each though; the small-bore one is smaller

Primary Gear – Bush Problems

Although not of immediate interest to many road-runners/street-burners, mainly accorded to the racing scene, it seems to be a perplexing problem to a very large number of folk around the world, and has burned up plenty of telephone time.

part numbers: 13H2934, LUF10005, CE12, 22G109, DAM8889, DAM8887

With the cost of new primary gears spiralling ever upwards, and the availability of good, serviceable used ones, fitting new bushes to existing gears is becoming a more common solution. For some reasons for bush failures and rectification to stop it re-occurring, see article 'Primary gear - Bush problems'. Since there is no useful information given in any of the workshop or DIY manuals on this subject, following is my approach to dealing with the issue.

The first thing to get to grips with is which bush ...

Primary Gear - Bush problems

Although not of immediate interest to many road-runners/street-burners, mainly accorded to the racing scene, it seems to be a perplexing problem to a very large number of folk around the world, and has burned up plenty of telephone time. Distilling the myriad of 'the symptoms go like this' descriptions down from various languages it has been put to me in - the end result was always the same. The bushes at one end or other, and sometimes both, had failed in their duties. Incidentally - some of the confusion when trying to sort the problem descriptions was down to misunderstandings about which end of the primary gear is which. To put the record straight, the end nearest the engine is the FRONT end. Consequently the end nearest the flywheel is then the REAR end. The two biggest outstanding symptoms were severe oil leaks onto the flywheel/clutch assembly, and difficulty/impossibility in selecting gears.

Primary Gear - Setting end float

A fairly crucial part of how the primary gear operates is its tolerances and running clearances. End float is a continual problem as folk either ignore it through ignorance or lack of accessible information on how to do it, or belief special tools are needed.

Terminology: DTI - Dial Test Indicator Also, later factory assembled engine units (from about 1992 onwards) were built up using whatever thrust washers were available, since Rover were not making regular orders for all shim/washer sizes due to the forthcoming end of production. Consequently, many units left Rover with incorrect (usually too big) clearances. The primary gear was no exception. Too much end float and clutch disengagement is adversely affected, the gear floating up and down the crankshaft in unison with the clutch plate. The result is a graunching gear change since the plate isn't clearing the flywheel and pressure plate surfaces fully. Too little end float and the gear is likely to be pinched tight as it

C-AEA3240 - Replacement Fully-floating Primary Gear Bush. For 1275-Type primary ...

This bush is made to fit as many known 1275 primary gears - both helical and straight cut - as possible that use the original 22G109 type bush. There may be some exceptions where the manufacturer uses a slightly shallower bush housing

Clutch - Drive Strap Alignment

Drive Strap Alignment If the pressure plate clutch plate friction face needs re-surfacing, get it machined to clean it up. Make sure the engineering company doing the job records the amount taken off as once done, the recorded amount needs removing from the tops of the 'horns' that stick up to ensure proper clamping force is achieved. If this is not done, clutch slip is inevitable. If using a pressure plate of unknown history, it is IMPERATIVE the clutch drive straps are set at the correct height. Many get this wrong and end up with a slipping clutch for some seemingly unfathomable reason. The following should also be carried out if the flywheel has been machined, or of unknown history also: Place the pressure plate 'horns' upper-most on something to hold it off of the work surface but not interfere with clutch plate or flywheel. Place the clutch plate in position, with the protruding primary gear spline boss on the underside facing the work surface Place the flywheel in positi

DIAPHRAGM SPRING - Pre-Verto types

I'm ignoring the old original spring-type jobs here for the same reasons I wouldn't suggest using their flywheels! The first two can be lightened, see accompanying diagram. Limit removal of metal on the rear face to 0.120" to be safe, 0.150" if you're feeling brave/lucky. The third can be further lightened by carrying out the machining operation on the rear face as indicated in the diagram and as per previously stated dimensions. Do not remove any more material than indicated for any of these pressure plates as it will not only reduce their strength, but will also cause over-heating of the clutch. Too little material will not be able to absorb any excessive heat generated during spirited driving! Bear in mind what was said about lightened standard cast iron flywheels - the same applies here. Under no circumstances use lightened standard cast iron pressure plates in ANY competition disciplines. The SG iron items are suitable for full race use despite lightening operations, although f

PRESSURE PLATE- Pre-Verto & Verto types

There is an astonishing five other types generally available. For high-tech ones see 'Flywheels & Pressure plates - technical advances' part numbers: 22A598, 22G270, C-AHT230, Apart from very first one that should be avoided at all costs (cast in part no.2A3509), there is an astonishing five other types generally available. For high-tech ones see 'Flywheels & Pressure plates - technical advances'. 22A598 - Number cast in. Standard-grade cast iron 22G270 - Number cast in. High-grade cast SG iron as fitted to Coopers and Cooper Ss Quinton Hazel - Triangular in shape, but only standard-grade cast iron. C-AHT230 - Mini Spares high-grade SG cast iron, but cast pre-lightened. Farndon Engineering - Machined from steel billet. The first two can be lightened, see accompanying diagram. Limit removal of metal on the rear face to 0.120" to be safe, 0.150" if you're feeling brave/lucky. The third can be further lightened by carrying out the machining operation on the rear face as indica

Idler Gear - Setting End Float

A fairly crucial part of how the idler gear operates is its tolerances and running clearances. part numbers: 22A1545, 22A1546, 22A1547, 22A1548, 22A1549, DAM4822, DAM4823, DAM4824, DAM4825, GUG705563GM, AAU8424, ADU6033, CCN110, 2A3643, 22A152, 53K547, Terminology: DTI - Dial Test Indicator End float is a continual problem as folk either ignore it through ignorance or lack of accessible information on how to do it, or belief special tools are needed. Also, later factory assembled engine units (from about 1992 onwards) were built up using whatever shims and thrust washers were available, since Rover were not making regular orders for all shim/washer sizes due to the forthcoming end of production. Consequently, many units left Rover with incorrect (usually too big) clearances. The idler gear was no exception. Too tight a clearance and the idler gear will either seize solid when it gets hot, or destroy the thrust washer thrust faces in the comparably soft aluminium gearbox and t

GEARBOX - Up-Rating Drop Gears

The standard drop gears are fine for practically all road use - almost irrespective of power output. part numbers: DAM9373, C-STR123, C-STR124, C-STR30, C-STR30A, C-STR30T, C-STR30TA, C-STR230, C-STR240, C-STR250 Terminology - Drop Gears - Transfer gears (primary, idler and input gears) Large-bore - Refers to anything based on a 1275-type unit Small-bore - Refers to anything based on 850/998/1098 units Despite what many folk believe - they are more than strong enough, and will perform perfectly well if correctly set up. That means getting the idler and primary gear end floats right, and using new bearings for the idler gear at each re-build. Simply following the methods outlined in the relevant workshop manuals will achieve these simple goals. There are two problems with standard drop gears - the main one is the helical cut of the teeth, the other a very limited selection of ratios. The helical-cut teeth are essentially power absorbing - both from increased metal-to-metal c

Gearbox - Up-rating diffs and FDs

There’s a good selection of straight-cut final FDs available. Examine the FD table, and using information from

'Gearbox - Final dives, standard' and 'Gearbox - Formulae for car speed, etc.'

you can assess which would best suit your usage. Bear in mind that they’re noisy, make sure you select one that’ll fit your diff unit, and also consider that using drop gears will allow fine-tuning of the ratio where necessary. See

'Gearbox - Up-rating drop gears'

Gearbox - Up-rating diffs, FDs and ancillaries.

part numbers: C-BTA166, C-BTA167, DAM6624, BTA101, 2A7062, DAM5071, DAM6027, RPS1418, C-AJJ3385, C-22A1731, ...Read more

Crankshaft - Standard Production Crank Identification

Yes, contrary to what many say/express, all cranks are forged. None are cast. They wouldn't last 2 minutes in an engine if they were cast - they'd be way too brittle. Below is a list of crankshaft identification data by forging or stamped numbers - yes, contrary to what many say/express, all cranks are forged. None are cast. They wouldn't last 2 minutes in an engine if they were cast - they'd be way too brittle. The differences are in the material used, finish machining detail and any heat treatments applied. It is by no means complete and utterly correct/infallible since Austin/Morris, British Leyland, Leyland cars, Austin Rover, rover, et al were seriously prone to not adhering to specifications and applications lists. But it is better than nothing at all! 22A62 850cc - Early type with oil feed for primary gear, 1.375" dia. tail 22A63 850cc - Early type with oil feed for primary gear, 1.375" dia. tail

Engine - Identification Data Updated

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 850cc 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. 998cc 9WR Wolseley Hornet & Riley Elf Mk2, pre closed circuit breathing 9AD Austin, Wolseley Hornet & Riley Elf Mk2 with remote type gearbox and closed

Flywheel - Pre-Verto Types

The early spring-type clutch flywheels are of no use except where total originality is required on a concours car. The taper is too small and diaphragm pressure ring non-existent. No use to man nor beast. Part No Applications: C-AEG421, C-AEG420, C-AEG619, C-AEG620, 2A3657, 2A3658, 2A3659, 2A3512 With the exception of the fact the two-piece flywheel is two pieces bolted together - this and the later one-piece cast item can be treated as the same thing. They will universally fit all transverse engine cranks from 1964 onwards, so that should be easy enough. If all you can get is the hulking great 1300 type, then this too is as universal to fit, but I highly recommend you get that extra cast lump machined off of the outer edge as a bare minimum. Further lightening of these cast flywheels is possible by having metal machined off of the diaphragm side, from the outer edge of the diaphragm pressure ring outwards.

GEARBOX - How they work

Having decided on or even implemented a course of action to bolster the performance of your Mini’s engine, maximising it’s potential should encompass a good look at the gearbox.

GEARBOX - How they work

Having decided on or even implemented a course of action to bolster the performance of your Mini’s engine, maximising it’s potential should encompass a good look at the gearbox.

Clutch - Drive strap alignment

Drive Strap Alignment If the pressure plate clutch plate friction face needs re-surfacing, get it machined to clean it up. Make sure the engineering company doing the job records the amount taken off as once done, the recorded amount needs removing from the tops of the 'horns' that stick up to ensure proper clamping force is achieved. If this is not done, clutch slip is inevitable. If using a pressure plate of unknown history, it is IMPERATIVE the clutch drive straps are set at the correct height. Many get this wrong and end up with a slipping clutch for some seemingly unfathomable reason. The following should also be carried out if the flywheel has been machined, or of unknown history also: Place the pressure plate 'horns' upper-most on something to hold it off of the work surface but not interfere with clutch plate or flywheel. Place the clutch plate in position, with the protruding primary gear spline boss on the underside facing the work surface Place the flywheel in position.

Clutch plates - Pre-Verto types.

There are generally three types to be concerned with these days - standard pre Verto, fiber rally/race, and sintered race. All at 180mm diameter.

Standard-type plates. The pre Verto plate has a spring-steel centre section to which is riveted the lining. Between the linings are sprung washers. These take up some of the shock impact of engagement and slight surface imperfections of the flywheel and pressure plate surfaces. Providing a genuine Unipart/AP Lockheed one is used, it will cope with most fast road applications without any problems. This includes almost all road-going standard over-bores (+0.020” to +0.060”) and a vast majority of big-bores (1380/1400). That covers up to 110 bhp and/or 90lb ft. - both flywheel measurements of course!! It is the torque that causes more problems than out-right horsepower. It can also be used in the Verto set-up to improve judder/grip/slip problems experienced when using the 'correct' standard plate...

Engine - Identification data

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 850cc 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.