Bicycle Mechanics - Hollowtech II drag
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06-08-09, 08:50 PM
I just put together a new mountianbike. I installed my Hollowtech II crankset and took it for a spin and realized this new frame had a 68mm BB instead of 73 like my old one. I put the correct number of 2.5mm spacers in 2 on the drive 1 on the non drive and reinstalled the crank. It was significantly harder to slide the axel through the bearings and now the crank feels like it has a alot of drag. Don't see how the spacers could cause that?
I'm taking the bike on a camping trip tommorow and wondering what to do. Would I really notice some drag at the bottom bracket? I have a cartridge crank I could install.
There's a bike shop on the way I think I could stop by there and get the BB faced, but they may not be open.
Thanks for any advise.
06-08-09, 09:05 PM
Well, it is recommended for the external bearing type cranks to have your bb shell faced. So you rode without the crank properly installed and felt it performed better that way? Don't know why it would be harder to put the axle thru the bb cups just because of the spacers, though. There is an inherent amount of drag on the Shimano external bb cranks, each of mine has, but really only noticed when spinning the crank by hand without a chain, I don't notice it when riding, don't believe it's significant under load.
06-09-09, 10:18 AM
Besides unfaced BB shell, don't overdo the pre-load before tightening the crank pinch bolts. That pre-load adjustment crankarm cap bolt thingy is best installed with the torque specified by Shimano.
I use a ParkTool's BBT-9 for external BBs, and find it tricky to hit a good pre-load with the little knob the tool has for this purpose, having quite strong fingers from playing violine, guitar, piano, and many years of rock-climbing.
06-09-09, 10:47 AM
The bearing seals will also break in alittle as well.
06-09-09, 12:53 PM
The BBT-9 is capable of stripping. Most mechanics (myself included) suggest spending a few extra dollars for the BBT-19.
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