M with knock

remchuk · Apr 25, 2013

Well, the center main is BAD. At least it didn't spin.
So far I can only find the main bearings for sale as a kit, can't find the center thrust bearing individually.

So it looks like we replace all three mains.

Thanks for all the advice.

Soundguy · Apr 25, 2013

i figured you'd find a main bad with a knock that din't go away with spark plug wire disconnect.. rods will quiet up pretty good when you pull the plug.. etc..

IHpower · May 8, 2013

This is a long shot but the earlier M's had cast iron pistons. The iron pistons had looser tolerances so they made a knocking type noise. One of my cousins had one, it sounded like a 560 Diesel while idling!! Not a expert, just throwing out what little I remember from way back when.