I left the last article explaining the new changes for the 2025 season. Well Dad, Chris and I have been very busy over the past few weeks! We have bodywork to paint and engines and gearboxes to build. We have decided to tackle the gearboxes first. We would be fitting the Minispares clubman straight cut gear set and the straight cut drop gears (Part No’s: C-STN39 and C-STR30AEVO).

Only the drop gears are a mandatory change for the 2025 season, however we are allowed the straight cut gear set and the consensus from the more experienced drivers is that they are slightly more durable, so we opted for the straight cut gear set. These gears have been run in the Super Mighty Minis for the past 25 years with no major problems and are a tried and tested upgrade for 2025.

Disassembly commenced on dad’s gearbox; this was simple as it had only been rebuilt a year ago by Dan Heywood. The standard helical gears were removed and swapped with straight cuts. If you have ever put one of these gearboxes together you will know they are quite fiddly, luckily Uncle Chris has quite a bit of patience! All bearings were checked for wear and as they were only a year old, they all looked in good condition. We also had to change the differential for the new season, swapping the crown wheel and pinion gear for a 3.6:1 ratio unit. These were purchased, second-hand from Guesswork’s, and are in good condition. We disassembled the differential, and test fitted the output shaft and noticed some excess play in the differential crown wheel bush. Chris very carefully used a grinder to cut a slot in the bush to split it for removal, then it could be punched out. Looking at where the bush sits it has a serrated edge to allow the bush to grip onto the crown wheel. Next was the task of fitting the new bush, this pressed in easily after some lathe work to get it to fit the shaft correctly. Chris mounted this into the lathe and bit by bit gradually shaved the bush down so the shaft fitted perfectly.

Once machined the differential could be reassembled. New lock tabs were fitted and all bolts torqued to the correct specification.

Moving on from the differential, the gear pack needed to be shimmed correctly as there was excess lateral movement, this was done with ease and then it could be fixed in place, although I did forget a lock tab therefore this will need to be ordered! The differential was slotted into place and once again this was shimmed to the required tolerance, preventing the differential from moving laterally in the housing. We managed to get this set up perfectly and I could then seal the casing and torque all the bolts to the required specifications. It really is satisfying doing gearbox rebuilds, making sure all components are perfectly clean and getting all the tolerances setup. The final item to shim was the straight cut idler gear. This required fitting the gasket and flywheel cover dry, then measuring the movement side to side in the gear. We found that we needed to change the shims, once changed the idler gear’s tolerance was perfect. We now have car 64’s gearbox complete. My gearbox, car 32 will require new bearings and a good clean!

With car 64’s gearbox complete we repeated the same process with my gearbox. It had all new bearings fitted and went together nicely. We then moved onto the engines, the blocks were cleaned by Dad and I to remove any unwanted debris. We then cleaned the crankshafts ready for these to be installed into the cylinder blocks. My engine being a slightly earlier 1275 A+ block did need some different crank main bearings. This was rectified and they dropped in nicely, plastigauge was used to check the clearances and we could torque the cranks in place. Then came the pistons, this is where we had some issues. I had bought a cheap piston ring compressor tool not realising the pistons on mini engines do not work well with this tool! Therefore, Chris made his own tool using some metal, pliers and a large jubilee clip, this worked well and 3 hours later we had all the pistons installed. Clearances were once again checked, and the pistons could be torqued to the correct specification. We were making good progress, camshafts next. These are new cams for 2025 (although they were the old Super Mighty Minis cams) from AC Dodd, cleaning was undertaken to remove all the wax, and the camshaft bearings were cleaned in conjunction with the lifters.

These were carefully installed and oiled to prevent rusting of the parts. The oil pumps could then be stripped, checked and cleaned and packed with assembly lubricant. Then bolted to the block using gasket sealant and the gasket from Minispares’ engine block kit. I then fitted the double chain adjustable vernier timing gear to the front of the engine, shimming the gear on the crankshaft to make sure the alignment was correct. We managed to get this all done over the course of two half days.

Once all these items were installed it was time to get the timing of the camshafts correct. This was done using a timing disc and homemade pointer. Chris and dad did the calculations and got it spot on. This was something which I didn’t understand at first however I managed to understand it fully by the end of this process. I could then install the cylinder head bolts and clean both faces to apply the head gasket. This went nice and smoothly, luckily no issues. All nuts were torqued and marked so we didn’t forget to do any up. The next stage is to finish the engines and get them fitted to the gearboxes. We hope to have this done within the week ready for fitting into the cars.

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