Small Block Mopar Thrust Bearing issue
 

I haven’t ever seen this before, but the crank looks to be pushed forward from the torque converter and is wearing down the thrust bearing. This is a cast crank 340; there is about a 1/8 to 3/16 gap unbolted between flex plate and converter. Spins freely, and moves back and forth easily. The forged crank 340 has no problem with same Trans and converter. Any ideas?? Thanks,
Mike

Re: Small Block Mopar Thrust Bearing issue
 

Did you check the end play with a dial indicator on the crank with the main thrust torqued to spec. ? Some I have checked have been zero or .001. I have almost ALWAYS had to sand the main on a piece of glass with fine grit paper to get the correct end play on 340's and 360's. Sometimes 426/440 engines also. Hold them together by hand and use a little WD-40 or ATF and sand a little of each thrust surface (front and back) in a circular motion using the glass plate or a granet surface plate with the fine grit paper and lube to keep the bearing halfs together and flat then wash them check again. If you take to much then its new bearing time.
Of course you might have another problem but I found this to be a good fix in my case as the same problem came about on a 340 several years ago. I used to do it on 428 S/S Ford CJ's also.

Re: Small Block Mopar Thrust Bearing issue
 

what part of the thrust bearing is showing wear?

Re: Small Block Mopar Thrust Bearing issue
 

if the thrust is worn on the back side another words look like crank is moving forward. its most likely the converter is putting pressure on the crank ,or something in the tranny is at fault. also check timing chain alignment.

Re: Small Block Mopar Thrust Bearing issue
 

Converter Balloning or Input saft to long on a 4 speed

Re: Small Block Mopar Thrust Bearing issue
 

What I have seen that has caused excessive thrust clearance is misaligned pulleys on the front of the engine....this creates pressure forward or rearward on the crank causing either the bearing or crank flange to wear....it takes very little misalignment to create this internal drag especially with a V-belt set up.....


D L Rambo.....

Re: Small Block Mopar Thrust Bearing issue
 

check the back of the crank where the pilot bearing would be. have found that to be the problem even with convertor spinning free. do not have any measurements.


Ron Waters s/st 1346

Re: Small Block Mopar Thrust Bearing issue
 

Converter ballooning, had it happen even on a low 12-sec bracket car. Had too much line pressure in the valve body at the time, too... no idea if that had any part in it.

Re: Small Block Mopar Thrust Bearing issue
 

If any part needs surface lapping. It should be done in a figure "8" pattern on a surface plate(glass or a highly finished checkerboard steel lapping plate). This is how I was taught when we used to rebuild fuel injection components.

Peter

Re: Small Block Mopar Thrust Bearing issue
 

do you use a two step ????,also cold runs with thick oil will wipe out the thrust ,,there is a procedure you can do to help this gmonde