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Trouble mounting Campy crankset(8 posts)

Trouble mounting Campy cranksetdawgcatchr
Jul 3, 2003 12:11 PM
Hi. I am putting a 10-speed Chorus crankset on my Colnago. The crankset is slightly used, less than 1000 miles, and is going on the standard 102mm Chorus BB. When installing, I am noticing that the chainrings are coming awfully close to the chainstays of the frame. Furthermore, the driveside crankarm is pulling onto the BB spindle more than the non-driveside crankarm, by about 1-2mm. The driveside crankarm also clears the chainstays by about 2mm less than the non-driveside crankarms.

How much clearance should exist between the chainrings and the chainstays? I am worried that somehow the drive-side crankarm spindle-hole is larger than it should be, causing the crankarm to slide further onto the spindle than it is designed for. This could theoretically pull the chainrings into the carbon stays of the bike, which would be a bad thing, or at the least cause chainsuck and bad shifting. Is the drive-side Chorus crankarm designed to slide further onto the BB than the non-drive side?
Jul 3, 2003 12:38 PM
Any chance the bb is backwards? (if this is possible)

Slightly used should not have worn the tapers too much, unless some ham-fisted tech overtightened the bolt a lot.

If it's not touching the frame, I wouldn't worry. I've had several that get very close.
the instructions....C-40
Jul 3, 2003 12:48 PM
are at this site:

The chainline should measure 43.5mm from center of frame to the center of the space between the chainrings, as shown on the instructions. This isn't real easy to measure.

Don't know how you've determined that the right side is pulled further onto the spindle, but the only good way is to accurately measure from the edge of the frame to the face of the crank arm, near the pedal. You'll need a precision (machinist's) scale for the job. The crankarms should be symmetrical. A 1mm difference at the end of the crankarm is no big deal, but 3-4mm would indicate a problem.

The BB is symmetrical and the bottom bracket shell on a properly made frame is centered in the frame. For what it's worth, I have 6mm (1/4") from my right chainstay to the inside of the little chainring.
How I compared the distance of crankarm onto spindle..dawgcatchr
Jul 3, 2003 3:32 PM
What I did to measure that the right crankarm is further onto the spindle than the left arm is install both sides. Once there, I removed the crank bolts and used calipers to measure the distance between the end of the spindle and the outer crank hole (which houses a crank puller). According to the torque wrench, both cranks were installed to the same Newton-meter setting. What I am afraid of is that whoever owned the crankset before me over-tightened the driveside, therefore enlarging the spindle hold (it slides on awfully easy). I will try to measure the inner spindle hole with calipers and compare to the left crankarm.

If this is the case, what distance is "too close" as far as the chainrings being close to the chainstays? I am putting these parts on a new CT1, and the last thing I want to do is damage the stays with a rotating buzzsaw of chainring.
same thing.desmo
Jul 4, 2003 8:13 PM
Been going through the very same thing on a friends bike. All low mile Campy Record, but not maintained well and ridden very hard. When swapping the parts on to a new frame after a crash the driveside crank was just a hair away from the chainstay. You could see that the arm was going way too far on to the spindle as it was almost touching the cup. The cranks had not been removed and replaced a lot but I think he rode them with loose bolts for awhile and enlarged the taper a bit. There was no way to ride the bike hard now without the crank hitting the chainstay. This was with a new Chorus BB, which was then shelved for a new Record BB. Even though they are the same spindle length etc. the Record one was a little better. But the only way to get enough clearance between the chainstay is to run a spacer between the driveside cup and BB shell. Probably what you will have to do to run those cranks.
take it out to dinner and a movie first....(nm)gregario
Jul 3, 2003 12:49 PM
now that's funny nmDougSloan
Jul 3, 2003 12:50 PM
whew! didn't get busted by the moderator!gregario
Jul 3, 2003 12:53 PM