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big end woes

I’m having a go at replacing the big end and have already run into problems.

The new pin doesn’t seem to want to fully enter the taper in the flywheels. There is around 20 thou between pin shoulder and flywheel when I put the pin in and that goes down to around 10 thou with 80 odd ft lbs tightening, and the crankpin shoulders don’t want to contact the flywheel face. The tapers look good and a smear of blue shows even contact, no ridges etc. The new pins (got 2) both fit like this in the flywheels in question and a couple of others I have lying around. Old pins fit all the flywheels with about 10 thou between the shoulder and flywheel face before tightening. Do the pin shoulders have to contact the flywheels? The separation between the flywheels is going to be greater than before by the look of it and confuse the timing side shaft and oil pump drive positioning.

Any suggestions what I may be doing wrong so far?


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Re: big end woes

Ian will know I'm sure. But I have a feeling that some crank pins were made slightly bigger on the taper to take up wear in the flywheels. Ron

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Re: big end woes

The taper is pulled into the wheel as the nut is tightened..This stretches the flywheel and produces a heavy interference fit.

The shoulder should also be pulled up against the flywheel so that the pin is supported on the taper and the shoulder...

Check to see if there is a burr at the outer end of the flywheel taper...There usually is. This is thrown up by the fitting of the last pin. Carefully remove any burr with a half round file taking care not to contact any other part of the taper...

Also check that the chamfer on the inner edge of the flywheel taper is sufficiently large to accommodate the radius ground into the crankpin shoulder...

Tighten to 100-110ft/lbs when fully tightened............Ian

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