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

Re: Small Block Mopar Thrust Bearing issue
 

As said in an earlier post check the back of the crank. I have had this issue with two different cast cranks. The cranks werent machined deep enough. Inspect it with a light and see if there are any contact points.Something I also do is drill a small hole through the bearing into the main bearing oil hole to provide positive oiling to the thrust. Good luck.

Re: Small Block Mopar Thrust Bearing issue
 

Ken,
Thanks for the input. Will check the crank again.
Mike

Re: Small Block Mopar Thrust Bearing issue
 

gmonde, not using a two step. Only the rearward side of the thrust bearing is being damaged. Thanks for the response.
Mike

Re: Small Block Mopar Thrust Bearing issue
 

Mike,
The converter is due for a freshening up and we were planning on sending it out anyways. Thanks for the response.
Mike

Re: Small Block Mopar Thrust Bearing issue
 

D L Rambo, Will check that out also. Thanks for the response.
Mike

Re: Small Block Mopar Thrust Bearing issue
 

Ron, will check the crank again. Thanks,
Mike

Re: Small Block Mopar Thrust Bearing issue
 

Peter, Thanks.
Mike

Re: Small Block Mopar Thrust Bearing issue
 

Thanks to all that have replied, I was thinking converter and will look closer at other possibilities.
Mike

Re: Small Block Mopar Thrust Bearing issue
 

There is a lot of info on the net. Do a search for thrust bearing problems. and look for the AERA paper on diagnosis and symptoms. most likely restricted coolers or cooler lines cause the torque converter to be pushed forward causing thrust problems. check your cooler line pressure.

Re: Small Block Mopar Thrust Bearing issue
 

I had problem with imput shaft on my 904 being significantly Bent.....Also I would dial indicate end of crank flange.....I have seen Cast small block cranks becoming seriously bent.

Re: Small Block Mopar Thrust Bearing issue
 

Mike,
The drilling for positive oil is a good idea. I use a less labor intensive way to oil the thrust.
Take the top(block side) main bearing and use a file to make a small angle cut right at the parting line. You do it only on the back side of the bearing on the thrust side. I usually do both sides of the bearing. You slot it on the portion that the crank journal runs on so the oil goes into the cavity that makes the roll into the thrust face. I don't slot the thrust face. Take a little scotch brite and smooth the edge it rolls up on the bearing. It doesn't take much of a slot/angle to provide positive oil feed from the main bearing feed to the thrust. Get the converter fixed.

Re: Small Block Mopar Thrust Bearing issue
 

Adger, Thanks for the info on the thrust bearing modification. I like the less aggressive way you suggested. Is it possible for you to send an illustration to me? My e-mail address is mc340dart1@aol.com. Thanks again,
Mike

Re: Small Block Mopar Thrust Bearing issue
 

Adger, Thanks for the info on the thrust bearing modification. I like the less aggressive way you suggested. Is it possible for you to send an illustration to me? My e-mail address is mc340dart1@aol.com. Thanks again,
Mike