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Smith
 Post subject: Odd Crank Problem
PostPosted: Tue Jan 15, 2002 1:39 pm 
About 14 months ago, we built and installed a 6 for my brother's daily working truck. Used a mid-70's core engine complete (head, block and crank), and had all the correct machine work done at a good local shop. Crank was just polished, and line bore on the mains was perfect. Used all Clevite bearings, pistons and rings. Now when we rev up the engine with no load, the crank appears to move forward (towards the radiator) about a ¼"±. I did check the crank end clearance when I set the main bearings, and I did "seat" the thrust bearing before I torqued the main bolts. Crank and block are from the original core engine, never rebuilt, and all dimensions were within spec. Real puzzle. Could the auto transmission be causing a problem? There are no abnormal noises or grinding when this happens, and the engine to date runs and drives great. Because it is very high geared (2.80±), and weighs 5,000#+, it is not a drag truck but the on highway performance equals a stock automatic late 80's 318 V8. Anyone have any ideas? We may pull the pan this weekend if we can without removing the engine just to look at the crank and main bearings.

sgw041454@aol.com
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Doc.
PostPosted: Tue Jan 15, 2002 2:28 pm 
Sounds like the thrust surface on the #3 main bearing has failed for no good reason. Can you move the crank fore and aft with a big screwdriver placed behind the front damper? (be easy on the force, it won't need much)

I see this failure much more with manual trans & stiff clutch set-ups, why this happened on an automatic will take some looking / testing.
Time to pull off the pan and take a look.
DD
Quote:
:
: About 14 months ago, we built and installed a
: 6 for my brother's daily working truck.
: Used a mid-70's core engine complete (head,
: block and crank), and had all the correct
: machine work done at a good local shop.
: Crank was just polished, and line bore on
: the mains was perfect. Used all Clevite
: bearings, pistons and rings. Now when we rev
: up the engine with no load, the crank
: appears to move forward (towards the
: radiator) about a ¼"±. I did check the
: crank end clearance when I set the main
: bearings, and I did "seat" the
: thrust bearing before I torqued the main
: bolts. Crank and block are from the original
: core engine, never rebuilt, and all
: dimensions were within spec. Real puzzle.
: Could the auto transmission be causing a
: problem? There are no abnormal noises or
: grinding when this happens, and the engine
: to date runs and drives great. Because it is
: very high geared (2.80±), and weighs
: 5,000#+, it is not a drag truck but the on
: highway performance equals a stock automatic
: late 80's 318 V8. Anyone have any ideas? We
: may pull the pan this weekend if we can
: without removing the engine just to look at
: the crank and main bearings.


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Smith
PostPosted: Tue Jan 15, 2002 3:48 pm 
Quote:
: Sounds like the thrust surface on the #3 main
: bearing has failed for no good reason. Can
: you move the crank fore and aft with a big
: screwdriver placed behind the front damper?
: (be easy on the force, it won't need much)


Very easy to move the crank with a bar when the engine is off. I agree that the #3 bearing thrust surfaces are going away but very puzzled about why. Again the crank was in very good shape when installed, and the block was like new. This is not the first engine I have done (many air cooled VWs, various B&S engines, F### V8s, etc.), and I have never had a failure like this before. Have a set of TRW bearings on the shelf, if the #3 bearing is gone, and the crank OK, I think we will just install the lone #3 and see what happens, assuming that the engine pan comes off. Thanks for the input.


sgw041454@aol.com
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Stan
PostPosted: Wed Jan 16, 2002 4:10 am 
I had a simular problem with a 360 I rebuilt. The engine had been used with Nitrous and a 4 speed. It destroyed the back half of the thrust surface on the crank. I missed it during the rebuild, checked thrust on every other motor I have built and they always checked ok, so I didn't check this one. On start up the crank would move .1 to .2 inches in and out. I ran the motor 20K miles with no trouble but it's out now to get fixed. I will check them ALL from now on. Do you know who supplied the bearings? The pan off might answer some questions, good luck.

aiton@aatd.eustis.army.mil
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bud L.
 Post subject: Re: Odd Crank Problem
PostPosted: Sat May 25, 2002 8:34 am 
I think I remember reading something years(Hell decades) ago, about something similar. I can't remember the specifics, but recall it had something to do with too much pressure in the auto trans or trans cooling lines. It's a more common problem with heavy loads in the cluth/pressure plate applications. Sorry, I can't be more specific, but it was a long time ago. It should point you in the right direction anyway.
Quote:
:
: About 14 months ago, we built and installed a
: 6 for my brother's daily working truck.
: Used a mid-70's core engine complete (head,
: block and crank), and had all the correct
: machine work done at a good local shop.
: Crank was just polished, and line bore on
: the mains was perfect. Used all Clevite
: bearings, pistons and rings. Now when we rev
: up the engine with no load, the crank
: appears to move forward (towards the
: radiator) about a ¼"±. I did check the
: crank end clearance when I set the main
: bearings, and I did "seat" the
: thrust bearing before I torqued the main
: bolts. Crank and block are from the original
: core engine, never rebuilt, and all
: dimensions were within spec. Real puzzle.
: Could the auto transmission be causing a
: problem? There are no abnormal noises or
: grinding when this happens, and the engine
: to date runs and drives great. Because it is
: very high geared (2.80±), and weighs
: 5,000#+, it is not a drag truck but the on
: highway performance equals a stock automatic
: late 80's 318 V8. Anyone have any ideas? We
: may pull the pan this weekend if we can
: without removing the engine just to look at
: the crank and main bearings.



fglmopar@aol.com
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