why did my rear thrust bearing surface go out?
 

7.4MPI with a M1 5 PSI pulley. 600hrs (100 with the procharger). Pulled the crank and found the rear main thrust surface (inboard) on the crank worn and the bearing surface lunched. First thought was the out-drive shaft pressing against the crank however it is worn inboard which says that if as a result of end pressure it would have come from the dampener side. Any ideas as to what might have caused this ware?(98 gen5)

Re: why did my rear thrust bearing surface go out?
 

Pulley alignment with the supercharger?? Long shot I know.

Re: why did my rear thrust bearing surface go out?
 

Thanks I will look @ it

Re: why did my rear thrust bearing surface go out?
 

What were the highest oil temps you were seeing? What did oil pressure do after wot runs?

BT :cool:

Re: why did my rear thrust bearing surface go out?
 

Check the bell housing alignment.You may need off set dowels from the block to the bell housing.

Re: why did my rear thrust bearing surface go out?
 

You should always pre-check end clearances on the main bearing thrust face while a motor is in the assembly stage, I don't offer this as criticism because most likely that you did but some forum readers get their info here and its important to stress good build procedures. When checking the end clearances it is also important to first whack he ends of the crank with a hard mallet in both directions to seat the rear main bearing absolutely square in its bore after the crank is assembled in the block. Then check the end clearances and make sure they are adequate. If this was done and the clearances were correct, then this means something else was pushing the crank backwards in the motor. I would suspicion that the pulley aligment on the front of the motor was not square and in-line and that the blower belt pulley may have been pre-loading the crankshaft back in the motor or the crankshaft cam gear may not be in proper alignment.. Wear on both thrust faces would indicate inadequate end clearances, improper oiling or bad line bore or hone and wear on the back thrust would indicate that pressure was coming from the drive or coupling areas. Just some thoughts.

Ray@Raylar

Ray @ Raylar

Re: why did my rear thrust bearing surface go out?
 

Thanks to all for your ideas. The oil pressure @ WOT starts @ 60+ #s and goes to 55#s after a hard run. Idle pressure is down to 20+#s after a hard run and back to 35#s with a cool down. I placed a probe on the oil filter and saw 190F during a hard run. I did not assemble the engine, Merc did, but I will check the thrust Clarence as suggested. I can only check the Blower pulley alignment and cam alignment upon assembly. The worn thrust surfaces are inboard on the rear bearing implying end pressure coming from the front of the motor