Originally Posted by
samkl
That brings up another thing, which I never heard of: that you shouldn't grease the crank arm bolts before tightening. What could possibly be the rationale?
I can think of one or two.
First, if a bolt is not going to be torqued anywhere near its maximum, then it's highly unlikely it will gall. That is the case with crank bolts. Torque values tend to be around 60-70% of yield strength. Campagnolo's torque spec is in line with general torque values for 8mm dry bolts.
Second, A dry bolt is less likely to loosen than a lubed one if under-torqued, because of friction. (BTW tapered fits maintain their hold through friction, so this is also an argument for dry tapers.) Bolts also maintain their hold by being in tension, and an under-torqued bolt might not have enough tension to stay secure.
A dry bolt is also less likely to be over-torqued. So maybe their recommendation is to build in a margin of safety against both those problems.
To that point: Torque values for lubricated bolts are 10% lower than dry because there is less friction. So if you want to lube your Campagnolo crank bolts, you can, but reduce that torque by the 10% so you don't overdo it. If you want to lube your tapers, you can, but reduce the torque even more to keep from over-installing the crankarms.
Or you can just follow Campagnolo's recommendations. It really is about manufacturer recommendations when it comes to such things. Some bolts are tightened to a torque spec, whether dry or lubed. Some are tightened to snug, then clocked an additional fraction of a turn. (This is the best way to keep from over-tightening pedals, BTW. Take them 1/16 turn past snug. No more is necessary.)
The square taper crank has been around for about 80 years. Campy's been making them for about 60 years. Engineers generally have this stuff figured out. So if you deviate from their recommendations, you should have some idea of how to compensate.
Different materials also require different torque values. If you use titanium crank bolts, they will have a much different torque spec than an 8.8 steel bolt. Much lower, in fact, about a third of 8.8 steel. (Which is why you should tighten the cranks on the taper with a steel bolt, then remove the steel bolt, and then put on the titanium.)