Seems like I have a lot of play in the crankshaft of a 1979 2F engine - approx 2 mm. Have been told the thrust bearing is the problem (very worn) and the full main bearing set should be replaced. Only has about 12K miles on engine rebuild done by previous owner (rebuild actually done by Yamato Engines in Washington State - they are now a Jasper owned shop). Any suggestions on what could have caused the excessive wear on the thrust bearing? It appears to be worn on the back side (clutch side) of the bearing. Also, is it reasonable/adviseable to just replace the four main bearings and not the connecting rod bearings at the same time? I have the engine on a stand as I'm doing a frame off restoration - I'm detailing the engine now - all bead blasted parts and new gaskets all around. Any suggestions/advice would be helpful