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Tractor Talk Discussion Forum

scratch on crankshaft

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sricks

08-09-2004 09:22:06




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I have a 6AT3.4 which has a spun rear main bearing. It was a military surplus unit that drove a compressor and generator via belts (180 degrees apart) directly off the flywheel pulley. I assume the loading was not very even and this is what caused the rear bearing and seal to fail. I have pulled several other caps and all the other bearings look fine. Slight scoring on crankshaft. Is it foolish to believe I can polish it out OK, put new bearings in and put the engine back in service. Should I just junk this thing or is it worth resurrecting. New bearings will run about $600 from Cummins.

Thanks for your suggestions.

Scott

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TheRealRon

08-09-2004 09:48:14




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 Re: scratch on crankshaft in reply to sricks, 08-09-2004 09:22:06  
If by "slight scoring" you mean something that won't easily snag a fingernail and there is no sign of heat discoloration on the rear main journal then I would say go for it. Do any polishing with very fine emery cloth. Polish only in the direction of rotation.

Of course, there are "slightly spun bearings" and "very badly spun bearings" and you must make sure that you can get the proper clearance with plastigage so check the rear main cap very carefully for heat marks and stress cracks. I know the crank is still in it so you can't check the block but if the cap is OK I'd say it's worth rolling the dice. The service manual will tell you if the rear is also a thrust bearing and if so then you must check end play too.

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Wayne

08-09-2004 20:46:07




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 Re: scratch on crankshaft in reply to TheRealRon, 08-09-2004 09:48:14  
I agree with Ron, if the spun bearing didn't damage the crank beyond the point of lightly polishing it then it should be servicable provided the clearance is still within specs. If your worried about a crack in the block or in the cap or whatever that can be checked for with everything together. There is a set you can get, I believe through Goodson, that is comprised of two magnets, one with a "active" North pole and one with a "active" South pole, and a magnetic/flourescent powder. If you place the the magnets on oposite sides of the block it basically polorizes the two sides of the crack, in effect turning it into a magnet. When you sprinkle the powder in the area in question it will be drawn to the crack. I watched the block man at our local machine shop use one of these sets the other day on the block he was getting ready to work on. It was amazing how the powder went straight to all the cracks, even the ones that couldn't be seen. Good luck with your repair.

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