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Advice sought on D/A BB problem(4 posts)

Advice sought on D/A BB problemStarliner
Aug 14, 2001 9:34 PM
Just had a frame built up with full D/A. With only 35 miles of riding, I came to my first big hill and as I began to really crank hard, the crankarms loosened and came out of phase. Suddenly instead of my feet being 180 degrees opposed, they came together.

I found the crank allen bolt on the chain sprocket side was loose so I rephased the left crankarm and tightened the bolt and continued on.

Trouble is, bolt keeps on loosening up after 20 or so miles and begins creaking when I mash down hard on the pedals.

Any advise before I take it back to the shop? BTW, the bolt on the crankarm side tightens in a normal clockwise fashion.
re: Advice sought on D/A BB problemnuke
Aug 14, 2001 10:39 PM
oh oh....hmmm....Well, I'm afraid that it could very well be the worst case. DA BB are splined interfaces into the crankarms. First, you said that while pedaling, the crankarm came loose and "came together". OK, well, that was the first fault. Whoever installed that crankarm, did it wrong.

The splined portions have to be lined up perfectly, and then the crank bolt installed and racheted down, carefully pulling the splines into the spline grooves. If they are offset, it could damage the splines (read: get a new crankarm & BB). It seems that the original installer had tightened the arm down such that the splines were not engaged into the spline grooves, but rather sitting on the offset face of the spline grooves, and simply tightened down there. As you rode the bike, very shortly afterward, the crank arm would become loose as you said.

Now...you then found the crank bolt loose, of course. And you tightened it. Well, if the crank arm's splines were not damaged before (and at best they would be slightly damaged) then you could have damaged then when you tightened the crankarm bolt on the side of the road UNLESS you got lucky and the splines lined up and everything went together smoothly.

So, what to do now? Do not ride the bike! You need to take it to a person that is experienced with DA splined BBs and have him take it apart and evaluate the damage. If the splines are tweaked, then it will probably go back together again, but it will be loose and creak and what not...certainly not the quality that you'd expect from a DA crankset.

If a shop installed the crankarms originally, then perhaps they will assume responsibility for the damage.

I feel for you, bud....
Gary
re: Advice sought on D/A BB problemdug
Aug 15, 2001 8:25 AM
What Gary said. Exactly. The LBS that did the install owes you a crankset.
re: Advice sought on D/A BB problemLC
Aug 15, 2001 10:43 AM
Usually the BB gets the most damage, but it could be both too.