RE: [CR]Greasing Threads and Tapers

(Example: Framebuilders:Tony Beek)

From: "Mark Bulgier" <mark@bulgier.net>
To: classicrendezvous@bikelist.org
Subject: RE: [CR]Greasing Threads and Tapers
Date: Thu, 1 Aug 2002 15:52:46 -0700


Chuck Schmidt quoted scripture (The Book of Jobst):
> "Once installed, a crank always
> squirms on its taper, and because the retaining bolt prevents it from
> coming off, it elbows itself away from the bolt and up the taper ever
> so slightly. This can be detected by the looseness of the retaining
> bolt after the bicycle has been ridden hard."

It should be added that this happens whether the axle is greased or not.

This is also the real reason for crank "dust caps", which aren't for dust at all, but retainers to keep the crank bolts from loosening further after crank squirm has occurred. Seldom necessary but it doesn't hurt.

The main practical advice is: DON'T keep tightening your crank bolts, though they seem to have less torque on them after riding. The lessened torque is inevitable and not caused by the bolts loosening. Chasing the cranks up the taper is what enlarges the hole and eventually cracks them.

I don't think the grease is necessary - lots of people get away fine without it. It just makes for a slightly more predictable, repeatable bolt torque and chainline, a little less aluminum deposited on the axle after a long time, and a reduced incidence of creaking or clicking noises. You do torque the bolts slightly less for the same chainline with grease than without it, but I torque them by feel anyway, which automatically takes the grease or lack of it into account.

Mark Bulgier
Seattle, Wa
USA