Bicycle Mechanics - Crank arm / chainring compatability

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UrbanSherpa
05-27-04, 01:09 PM
Cannondale RW700 road bike if it matters....

I recently had a problem with my left crank arm. Seems the bolt loosened and semi-stripped the octalink splines on the crank arm (BB is OK). Now I have to stop every few miles and tighten the crank bolt with my 8mm. (even with a torque wrench the bolt loosens). The crank is a Cannondale EX, and the Cannondale factory or dealers won't sell me a single left arm. The tech guy said I'd have to buy the set (cost way more than I should have to spend). I've decided to buy a 105, or Ultegra instead of the C'dale.

My question.... if I buy JUST the crank arms (w/o chainrings) will my 52/42/30 chainrings fit the Shimano stuff, are they standard/compatable?


Thanks for the info, -Karl

Revtor
05-27-04, 03:08 PM
If it tightens OK, and has no slop when its tight, maybe try some blue threadlock on the bolt that keeps coming loose. put a drop on the threads, torque it in and let it sit overnight.. shouldn't come loose. If the splines are too mangled then yeah I guess new cranks are in the deck for ya. Try Ebay for single arms. . .

~Steve
Retro Grouch
05-27-04, 06:45 PM
Shimano crankarms are 130/74mm bolt circle diameter.

Measure the center to center distance of any two adjacent chainring bolts. If yours measure 76.4mm for the big rings and 43.5mm for the granny, you have a match.

Incidentally, if your crankarm is coming loose that easily, I doubt the locktite trick is going to fix it.

madpogue
05-28-04, 03:46 PM
If the BCDs aren't the same, just put the left crankarm on; make sure, of course, it's the same length. Keep the Shimano right arm/spider on the shelf. Yeah, it'll look silly for now, but when your chainrings wear out, buy new rings to fit the Shimano right arm, and slap it on. Or just buy a complete set with the rings now if it's cheaper, but ride the existing rings / right arm until the rings wear.