I just built up my 3'rd M20.
I purchased this unit decribed as being rebuilt by a very reputible rebuilder.
I found many used & damaged
items inside when we popped the side cover open and after initial teardown.
Needless to say, I was not very happy!
The rebuild cost me, but after proper inspection and replacing with new parts,
I now have a really sweet M20.
Bad parts :
Cluster shaft badly pitted and worn
Countershaft Roller Spacer/Washers for some reason were indented by the roller bearings
Synchros were used
Clutch Hubs were both bad
Speedo Plastic gears were worn and broken
Maindrive Bearing was used
Worn engagement teeth
Reverse, 3'rd, and 4'th had damages to the actual teeth tips
Tail Housing threads had helicoils; typical
Main Case ended up being OK after many hours of detailing
1'st and 2'nd gear both were OK, oddly.
I ended up replacing all of the above parts with brand new pieces.
Some Italian, some typical rebuild parts.
I am going to post up a few images of the 3'rd gear and 4'th / Input shaft.
Someone before me owning this M20 ground down some of the engagement teeth.
Both engagement ground locations were at 6 & 12 o'clock postions.
I ended up replacing both with Italian Gears.
Can you folks tell me why someone did this to these gears?
The M20 completed; sorry for the fuzzy image.