Flash coating wiped off after a few turns of the crank?! - Hot Rod Forum : Hotrodders Bulletin Board
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Old 03-10-2012, 12:05 PM
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Flash coating wiped off after a few turns of the crank?!

Ok so, I had to take out the crank I spec'd out and dropped in on Tuesday because the bores need to be opened up about .001".

The crank bearing clearance is between .0023 and .0027 on all the main journals. I checked via a mic and dial bore gauge using a transfer method (measure journal, then zero out bore gage on mic etc...). Took five measurements of each bearing using the dial bore gage, just to make sure every one was within a tenth. I then double checked with plastigage just to be sure, everything matched up.
All journals had no appreciable out of round or taper that I could pick up. No knicks or roughness on any journals.
The motor was assembled with assembly lube and all surfaces had a nice coating. Bearings are 77 P's. Bearings have witness marks from dial bore gage but nothing to worry about. I spun the crank by hand probably a dozen or so times that night and it felt good, no binding or undue friction, just silky smooth.


Today after pulling out the crank I looked down and saw that the #2 main bearing has some light wear in the bearing on one side (see pics)... just through the flashing. The #2 Main bearing in the cap shows no wear. The one in the block does have the flashing wear.

The hell is going on here? Worry, dont worry?

NOTE: Bore Gage witness marks are very Exaggerated due to the flash. They are not near that profound.




I would have never of seen it had the crank not come back out. Sometimes ignorance is bliss.

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Old 03-10-2012, 05:00 PM
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Knock off the high spots with a Scotchbrite pad and run it.
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Old 03-10-2012, 05:23 PM
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Its been a few years

But I remember using lacquer thinner to rub down the inserts on the insides with a lint free clothe before lubing and installing them. This takes of the factory coating that the inserts come with.
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Old 03-10-2012, 09:38 PM
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so you all see nothing wrong with the bearing? Nothing im missing here?

I just fear the dreaded bearing spin...

**cringe**
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Old 03-10-2012, 10:08 PM
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Once you have oil pressure there won't be any contact between the bearing and crank. Tech's right their fine.
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Old 03-10-2012, 10:35 PM
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All is well.

Thats right all is ok with the clearance.
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Old 03-11-2012, 01:58 PM
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Quote:
Originally Posted by loudandproud
so you all see nothing wrong with the bearing? Nothing im missing here?

I just fear the dreaded bearing spin...

**cringe**
If you have made certain that the bearing bores are round and tight and you tune the motor properly to stay out of detonation, you will be fine. Smokey Yunick discovered that when the motor detonates, the pounding that the crank takes is transferred to the bearings and they will curl up like a potato chip. When this happens, the edge of the bearing insert will wipe all the oil off the journal and the show is over. You can see the same thing happen if you beat a piece of metal with a ball peen hammer. It will begin to curl up.

Take a look at the parting lines on the inserts and you'll see that they have a slightly larger diameter than the rest of the insert. The bearing manufacturers began adding those cuts after Smokey's discovery. You can beat on 'em a little bit without wiping the oil off the crank journal, but if the motor really gets into detonation, you're done.

Last edited by techinspector1; 03-11-2012 at 02:13 PM.
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Old 03-11-2012, 06:19 PM
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bearings

Never, NEVER polish off the coating on the bearing. If the bearing shows wear only on one side, then your crank is not straight. It will be okay for a street driven car, but if you plan to run it hard have the crank straightened by a reputable shop. Cranks must be straightened by hammer blows, NEVER by putting it in a press. As you may well imagine, only an expert should be doing this. And don't watch. It will scare you to death! lol
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Old 03-12-2012, 06:12 AM
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I wouldn't necessarily say it's a bent crank. Usually on a bent crank both bearings on the bent journal will show rubbing not just one. It might however be a main on the block that's out of alignment. Pretty easy to check with a straight edge. The other thing to look at is the back of the bearing for anything that might have gotten behind it during final assembly.
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Old 03-12-2012, 07:02 AM
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I agree w/engineczar. Also it could be a bad bearing. Swap that shell out for a different shell and repeat the same steps to see if the witness mark appears on the "new" bearing half. If it doesn't, either there was debris under the shell or the shell is out of spec.
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Old 03-12-2012, 07:29 PM
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Quote:
Originally Posted by loudandproud
Ok so, I had to take out the crank I spec'd out and dropped in on Tuesday because the bores need to be opened up about .001".

The crank bearing clearance is between .0023 and .0027 on all the main journals. I checked via a mic and dial bore gauge using a transfer method (measure journal, then zero out bore gage on mic etc...). Took five measurements of each bearing using the dial bore gage, just to make sure every one was within a tenth. I then double checked with plastigage just to be sure, everything matched up.
All journals had no appreciable out of round or taper that I could pick up. No knicks or roughness on any journals.
The motor was assembled with assembly lube and all surfaces had a nice coating. Bearings are 77 P's. Bearings have witness marks from dial bore gage but nothing to worry about. I spun the crank by hand probably a dozen or so times that night and it felt good, no binding or undue friction, just silky smooth.


Today after pulling out the crank I looked down and saw that the #2 main bearing has some light wear in the bearing on one side (see pics)... just through the flashing. The #2 Main bearing in the cap shows no wear. The one in the block does have the flashing wear.

The hell is going on here? Worry, dont worry?

NOTE: Bore Gage witness marks are very Exaggerated due to the flash. They are not near that profound.




I would have never of seen it had the crank not come back out. Sometimes ignorance is bliss.
Rather typical of some sort of dirt between the insert and saddle or a nicked spot on the saddle that bends the bearing up a couple millionths. Probably not a running problem since the crank will be floating on an oil barrier and in service won't contact the shell. The bearing looks ugly but reuseable. Engine oil is not an adaquate prelube, use an assembly lube, the grease in the formula should prevent this from happening.

Bogie
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