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cstreit cstreit is offline
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Join Date: Feb 2000
Location: Naperville, IL USA
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Strange main bearing wear. Any ideas WHY?

Okay so I'm doing a rebuild on this 2.0L race motor for a good friend/customer. The engine was over-revved to somewhere past 9300 RPM (Not typo, 9300+). A number of rockers were broken but it appears there was no piston to valve contact.

When I split the case I found that some of the main bearings are showing copper along the edge, maybe 2mm worth on the #4, #5, and #6 bearing. THe picture shows two of them. The wear is towards the #8 bearing end of the case.

Any ideas why?

My only theory so far is that when the crank was ground (it's .25mm undersize) the edges near the counterweights were left a little thick.

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2001 GT3 Cup - "Pepin"
1996 993 RS Replica
2008 Yamaha R6
1971 Norton 750 Commando
Old 05-25-2005, 08:43 PM
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