The bush in the intermediate gear of the M20 engine (and others) between the inlet cam and mag drive gear is quite prone to wear...
It never really gets 'terminal' and will run and run even when worn...
However, it's best to replace it periodically and keep the correct clearances for as long as possible...
It may not be so easy to source the correct bush, but one that is easier to obtain is the B31/33 small end bush...I.D and O.D. are the same as the gear bush but the small end bush is a little longer...It's a simple job to shorten it after fitting to the gear...
Coming back to the lubrication, the bush gets it's lubricant through the intermediate gear spindle, which is drilled through along its entire length...
A cross drilling and oil scroll then feeds the bush...
Crankcase pressure forces an oil mist through a hole in the crank case wall, through the centre of the spindle and to the bush....
If the gear spindle is removed from the crank cases for replacement or to blast the cases it is important that it is replaced with the cross drilled oil hole facing downwards...This allows any oil that 'pools' inside the spindle to reach the bush...
Also, care must be taken to ensure the bolt that screws into the outer end of the spindle is the correct length (5/8" under the head) and that a shakeproof washer is fitted...
If a bolt that is too long is fitted it will block off the cross drilled oil hole and reduce/cut off the oil supply to the bush...
Small details but worth getting right in this case....Ian
email (option): ian@wright52.plus.com