I purchased an M20 recently and was told it had been rebuilt and had stood a while. It started ok and selected the gears ok, however after changing the engine oil, 5 pints according to the service sheets, I now have quite a nasty oil leak primary drive side and I cannot select any gears, I believe the bike was rebuilt approx. 7/8 years ago and has been garaged , but started now and then, any ideas ?
Regarding the shift problem, can you shift the transmission through the gears while rocking the bike with the engine off?
If so, I would suspect a badly dragging clutch is causing the issue.
The massive oil leak from the primary case sounds as if engine oil is being forced into the primary because of wet-dumping or a poorly functioning oil pump.
The high oil level in the primary could have contaminated the dry clutch which could cause clutch drag, preventing proper shifting.
Several questions here, on how the bike was recommissioned after sitting for so many years. How much oil was drained from the tank and engine before refilling? How much oil was in the primary case before operation? Is oil visibly returning to the oil tank from the engine?
You can select gears with the bike on the stand without the engine running, but cannot with engine going, the level of oil is very high in the oil tank yet as I mentioned earlier it was measured exactly to 5 pints, however there wasn't a great deal came out I did drain both the sump and oil tank.
So, it may be that the transmission is not at fault, and that the shifting issue is with a dragging clutch, which will need to come apart for cleaning and inspection.
Are you seeing oil returning to the oil tank via the standpipe visible through the tank filler hole?
And, If you are not doing so currently, you might want to follow the forum thread below as it discusses a similar sort of oiling problem.
