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cstreit's Avatar
 
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Thanks Tyson. Wouldn't the opposite side of the 2-4 bearings show the same wear then, or does it not work like that?

I checked the crank for runout and found none, can you flex it without bending it?
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Old 05-27-2005, 12:33 PM
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Elastic deformation

HI Chris,
Yes, the crank can bend temporarily.
This is refered to as Elastic deformation, verses Plastic deformation which would show up as a bent crank.

Jeff
Old 05-27-2005, 03:00 PM
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All cranks flex all the time, its just a matter of how much. A crank normally flexes such a small ammount that it dosen't loose its shape or bend or break. That flexng is why cranks eventually wear out and break. Its just like bending a hanger wire back and forth. Bend it a very small ammount it will almost last forever before it breaks, bend it back and forth a lot and it breaks very quickly. Thats why old 356 cranks break quickly in an all out race car and new ones last much longer. In a stock 356 they almost never break. In a 911 everything is much better supported and the cranks are pretty bullit proof and only break because something else broke. If there is good oil pressure and nothing has broke to overstress the crank I would think it would be good for a very long time even in a race engine. My opinion is to champher the bearings and its as good as new. Narrower bearings will slightly improve the performance as well. If bearing width is still a consideration for some reason I would go to Red line oil which will more than make up for the narrow bearing.
Old 05-27-2005, 03:03 PM
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Thanks guys,

The owner uses Redline exclusively. After measuring everything else I am going to chamfer the bearings a bit and explain to the owner what I found. I think I'm really worrying about nothing here. THe only other option is to replace the crank and I don't think that's warranted at this point.
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2001 GT3 Cup - "Pepin"
1996 993 RS Replica
2008 Yamaha R6
1971 Norton 750 Commando
Old 05-27-2005, 08:33 PM
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Chris,
I vote with a lot of others here on the board; crank flex. If this was a mechanical over-rev, i.e. missed shift/improper downshift, the loads imposed on the bottom end went off the charts. Have the crank and rods blueprinted after they are magnafluxed. Cheap insurance.
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Old 05-28-2005, 06:49 AM
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Chris...I agree with chamfering before assembly because that will remove the metal from the engine before it gets a chance to wear away and end up in the filter....or aother worse places.
Bob
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Old 05-28-2005, 07:48 AM
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