Join Date: Oct 2004
Location: DC / Maryland suburbs
Bikes: Homebuilt tourer/commuter, modified-beyond-recognition 1990 Trek 1100, reasonably stock 2002-ish Gary Fisher Hoo Koo E Koo
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Check that the crank bolts are tight AND that the bolts that hold the chainrings to the crank are tight. You say that the bottom bracket is sound... have you removed it or done anything to it recently?
Basically all square taper cranks ever made have a standard taper EXCEPT for Campagnolo cranks and old Ofmega cranks I believe. So there's no difference between the taper design of old and new Shimano cranks. It is possible, however, for the tapered part of the cranks to become bent and worn, because the cranks are softer aluminum while the bottom bracket spindle is hard steel. Were you running the cranks for a while without tightening them sufficiently? If so, you may have damaged the taper...