Thread: junk crank

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I have a 74' 350 4 bolt main, 30 over, 2.02\1.60 heads, edelbrock performer intake, mild cam, doug thorley headers and flowmasters. The problem I have is the crank. The engine has less than 5000 miles on it and the thrust bearing has machined the crank to give me around 1\8 of an inch endplay. Could this be caused by bad finish on the crank or maybe lack of lubrication? Ive never run into this problem before and was wondering if anybody else has experinced anything like this before. let me know what you think.

Since posting this question Ive noticed that the powersteering pulley may have been out of alignment with the crank pulley. Could this have caused this??

Since the ps pump is connected through a flexable link (the belt) it should have no effect on crankshaft fore and aft movement.

The problem I have with your original question is that the bearing is a much softer material than the crank shaft. If there were wear between these two, it should be the bearing that sacrifices itself to not harm the shaft. Are you describing an actual observed condition at the thrust bearing surface, or are you speculating because you've measured excessive end play, but haven't done disassembly yet?

the forward thrust surface on the crank has been machined by what is left of the bearing. The edge of the bearing has worn a groove on the thrust portion of the crank. I would have never believed it until I saw it. Also the counterweights have just barely started rubbing block!!!! Any Ideas?

Hmmmm. Sounds ugly!!

It's a little tough to tell without seeing it, but.
I wouldn't expect a lack of lubrication because the thrust surface is fed by the same flow as through the bearings. If you'd wiped out the mains, or even the rod bearings, then maybe. If the thrust bearing surface and the crank thrust surface weren't parallel when first assembled, that would give a bad lubrication environment, but then, unless it was very far off, the premature wear of the bearing surface would have been "machined" into paralllel by the turning of the crank diminishing the problem. Has the engine builder, or the machine shop that did the work on the crank or block, looked at it and rechecked what measurements they can? Just some wild thoughts here; bearing saddle crooked, bearing cap installed incorrectly, crank turned incorrectly e.g. no fillet, crooked, wrong bearings, or end play not set correctly at assembly. Was the correct flywheel or flex plate used, could have affected balance, though you should have been able to feel something if it was wrong.

I take it there's no warranty here?

NO warranty. I tend to agree with bad initial assembly or a balance thing. The miles that this engine has were a move from california back home to michigan and I felt a steady vibration the whole way, assumed a u joint or mabye tailshaft bushing in the transmission( th350) never really found source of vibration. I removed the engine and noticed the excessive end play after I was rear ended and the truck was totaled. Now I am putting the engine in another truck and hoping a crank with new bearings and new oil pump will do the trick. I will probably also replace flex plate and check everything I can upon reassembly. What would you do if it were you?

Since you asked...............
I'd find the best engine guy/machine shop in my area to check everything about the block and rotating assembly to make sure a) it's saveable, b) they're the right parts, c) if they're WORTH saving. If all that can be done, and done economically, then make sure the flexplate is correct for that model engine/crankshaft. Not all Chev small blocks are balanced the same. I'm not that much of a chev expert to tell you which ones are internal balanced, and which are external, but I recall there are differences. Again, seek the local expert who can see and evaluate correctly, what you've got. Otherwise, especially with a Chev 350, a crate motor pencils out real well against a proper rebuild of a suspect engine. They have all sorts of choices, and most of your equipment aside from the shortblock will either transfer to a crate engine, or have some value, for example, on ebay. And they come with the General's warranty.

Thanks for all your help. Will see what we can do.

Originally posted by Bob Parmenter
Not all Chev small blocks are balanced the same. I'm not that much of a chev expert to tell you which ones are internal balanced, and which are external, but I recall there are differences. . [/B]

I am by no means an expert on the subject, but I've been told that 400 sbc's and 454 bbc's are the only two externally balanced Chevy engines.

Along with twospeed, check the torque convertor. If the convertor has "blued" from overheating, it can "balloon" and expand, causing excessive pressure on the trust surface of the main bearing. I've seen this on Chevys used for towing w/o a auxilary coolier. Sometimes the trans pump will go out at the same time.

In this months "Gears" magazine (for automatic trans people). There is an article on crank thrust failure. It describes the lube problems a thrust bearing has (surface finish, poor lube etc.). Tips to help avoid the problem. One thing mentioned is even a trans "shift kit" can cause crank thrust failure..

Most of the failures I have seen were from improper assembly, Cap mis-alignment (poor line bore/hone with non-stock caps), trans/flywheel problems and super heavy clutch/pressure plate assemblys.

Once the thrust is worn the only cure is replacement of the crank or have the crank thrust welded and re-ground.

While the newer contributions may be of some value in a general sense, please note that the originator of this thread posted nearly two years ago and hasn't been back since.

Other than the Torque converter...Which should automatically be replaced when the engine is...

I see alot of cranks installed that don't have the thrust surface clearance set right.....

I usually either clearence it with a dial-indicator and a prybar or put the harmonic balancer on with a rubber mallet....

To little clearence and you'll burn up the surface and it will ware pretty fast due to lack of oil and metal to metal contact...

looser clearence is more acceptable as you'll have good flow of oil around it so it won't ware near as fast....I run mine on the loose side usually...depends on the app....