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Steve@Rennsport Steve@Rennsport is offline
Registered User
Join Date: Jul 2001
Location: Portland Oregon
Posts: 6,984
Hi John:

Having raced 3.0 RSR's for many years, I have some first-hand experiences with these things,....

Indeed, the vibratory signature of the 70.4mm cranks did shake flywheels loose at 8000 RPM and that was a major issue. We resorted to many "creative" solutions to try keeping the flywheel attached as the RPM hit 8000 and above. Below 7900, no problem at all if it was assembled correctly.

This was/is a problem for all 70.4mm 6-bolt cranks and this was not fixed until the introduction of the 9-bolt cranks.

Further, RSR's had a special crank, rods and bearings with larger fillets at the rod journals to prevent high-RPM cracking. We also did other modifications to the crank, case, and bearings to get more oil to the #2 & #5 rod journals at the center of the crank; the last place to get oil.

One may use the 2.4-2.7 70.4mm 6-bolt crank as long as its properly prepared and with the understanding that its safe to 7800 RPM with all the mods. We also use aluminum flywheels to help keep them attached at those RPM levels.
Steve Weiner
Rennsport Systems
Portland Oregon
(503) 244-0990
Old 07-01-2005, 12:51 PM
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