Article on The Internet Mini Encyclopædia
There are 4 main primary gears:
The difference between A and A+ is finer teeth on A+ (to reduce noise), and the difference between 998 and 1275 is in the crank step.
The correct primary gear thrust washer must be used. 850 & 998 engines don't have a step on the crank, 1275 engines do have a step.
A and A+ crank tails are the same, so either can be used on either crank, but obviously the correct drop gears must be used and these are determined by which gearbox you have; you also need the correct primary gear for the engine size (1275 or 998).
There are two other rarer types. The early 850 crank had a 1.375" tail. Some of these were 'wet nose' meaning the gear was lubricated through a drilling in the crank. This was a bad idea as it lubricated the clutch plate also! Then they went to the Deva (self-lubricating) bush type primary gear but still with a 1.375" tail. Crank noses are now 1.5".
If you include Metro primary gears as well, there is an 'E' primary gear that has 30 teeth instead of 29. This takes it to seven types, but...
Rover list two 1275 A+ primary gears, the first for all models except MG METRO TURBO & GTA the second is for these models. The difference is in the hardness of the material. (The harder type is used in the Mini 1275 1992-> models). This takes it up to eight!
Primary gear thrust washers
How do I correct the primary gear end-float?
The primary gear thrust washer thickness denotes the end-float. They are available in standard and several thicker sizes. They cost about 15 quid each from Rover too. :-(
The end float is only really an issue if using helical gears, due to the side loading.
Running with a wider end-float will lead to noisier transfer gears, especially when idling.
Primary gear oil seal - changing with engine in the car
Brett Nicholson talks us through the process:
I managed to replace the primary gear seal with the engine in the car, and it wasn't too hard at all.
First I removed the top rad bracket and loosened the bottom one. Then I unbolted the clutch slave and tied it up out of the way, removed the starter and removed the bolts holding the clutch-side engine mount to the subframe.
The engine could then be jacked up on the clutch side far enough that there was approx. one inch clearance between the engine mount and the subframe, without undoing anything else or damaging the radiator. (I did not have to unbolt the remote, exhaust, sports air filter, engine steady or remove the radiator to gain enough clearance.) The bottom bolt on the clutch cover was difficult to remove, but I deliberately left out the rearmost bolt when I put the engine in last time (that bolt is impossible!). Soon I had the clutch cover completely removed.
From then it was a simple matter to remove the clutch diaphragm, undo the flywheel bolt (I always jam the ring-gear with an old main-bearing in the starter motor hole) and use the puller to remove the flywheel as usual.
I tried to remove the old seal using a screwdriver, but I was not making much progress. Eventually I removed the primary gear u-shaped retainer washer and thrust washer. Then I used a small two-legged puller to gently pull the primary gear and seal out of the housing. I cleaned up the inside of the housing and the primary gear before fitting a new, lightly greased seal to the primary gear, using masking tape to protect the seal from the gear teeth.
The primary gear, with new seal sitting on the sealing area was put back on the crank and the primary gear turned until the primary gear just started to engage the idler gear. An off-cut of thick-walled exhaust pipe of similar diameter to the outer diameter of the primary gear seal happened to be lying around. So I made up a small 1/8 inch x three inch x three inch metal plate with a hole in the centre. The tube was slipped over the primary gear and the plate bolted to the end of the crank using the standard flywheel bolt.
Gently tightening the flywheel bolt eased the seal and the primary gear into place, until I could see the seal had been pushed in far enough. Too easy!
A new clutch plate was required, I cleaned up the flywheel and back plate and bought a new clutch as the old one had been contaminated by oil. Finally I refitted everything - reversal of the removal procedure as the manuals say!
Three hours work and I was back on the road.
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20 May 2003