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Replacement Left Crank Arm - Does Brand Matter?

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Replacement Left Crank Arm - Does Brand Matter?

Old 01-14-15, 03:11 PM
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lanciat
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Replacement Left Crank Arm - Does Brand Matter?

While restoring an old Cannondale hybrid, I managed to strip the threads on the left side (non-drive side) crank arm while trying to remove the crank (much to my surprise, the Park crank puller simply pulled the threads right out).

I eventually was able to remove both crank arms using heat, but now the left side arm is ruined (that is, if I ever expect to get it off again after re-installing). Drive side crank arm is fine.

My question is whether I can use a generic left side crank arm of the same 170 mm length (Sugino makes some nice ones), or am I better off looking for an exact replacement (circa 1991 Deore LX, which will definitely be more difficult to source). Existing bottom bracket spindle is 122.5 mm, which is quite long by today's standards for a triple crank. Modern Sugino crank arms are intended for a 110 or 113 mm spindle, but I'm thinking that it should be completely irrelevant insofar as the left crank is concerned. Using the original drive side crank arm, I'll experience no change at all in shifting performance.

Any thoughts on this?
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Old 01-14-15, 03:23 PM
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I'd just about bet that by the end of today, one of the helpful folks here will post that they have what you need. If not exactly, I'm sure it will be close.
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Old 01-14-15, 03:46 PM
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I'd be careful. Different cranks require different spindle lengths in part because they have a different curve. TA cranks require longer spindles because the arm goes basically straight up, whereas a campy or sugino need a shorter one because the crank arm curves out. If the spindle and crank curve don't match up, the end of the crank arm will be at a different Q-factor than you want to match the drive side. Lots of things could go wrong.
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Old 01-14-15, 03:54 PM
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I agree with icepick. Mechanically it may seem fine but you could have big trouble if that significantly closer or farther from the centerline of the bike than the drive side.

If you live in a big city/metro area and have some real old shops you might get lucky and find a shop that has the kit to put and oversized (I think TA threading) single key release / self extractor in the crank.
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Old 01-14-15, 04:08 PM
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Originally Posted by lanciat View Post
While restoring an old Cannondale hybrid, I managed to strip the threads on the left side (non-drive side) crank arm while trying to remove the crank (much to my surprise, the Park crank puller simply pulled the threads right out).

I eventually was able to remove both crank arms using heat, but now the left side arm is ruined (that is, if I ever expect to get it off again after re-installing). Drive side crank arm is fine.

My question is whether I can use a generic left side crank arm of the same 170 mm length (Sugino makes some nice ones), or am I better off looking for an exact replacement (circa 1991 Deore LX, which will definitely be more difficult to source). Existing bottom bracket spindle is 122.5 mm, which is quite long by today's standards for a triple crank. Modern Sugino crank arms are intended for a 110 or 113 mm spindle, but I'm thinking that it should be completely irrelevant insofar as the left crank is concerned. Using the original drive side crank arm, I'll experience no change at all in shifting performance.

Any thoughts on this?
Don't know about the compatibility of different arms but have been in the position where stripped out thread could potentially ruin an expensive part. (Think motorcycle engine head.) When that happened, I had a machine shop install a helicoil insert to save the part. Don't know what sizes helicoils come in, mine work was on a relatively small bolt diameter, but you might just be able to salvage that arm.

Just a thought...
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Old 01-14-15, 04:17 PM
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I do not think it is absolutely critical the left arm matches the right arm. When you replace an asymmetrical spindle with a symmetrical spindle, the left spindle sticks out more but is not noticeable when riding. I think matching the crank arm length would be more important and more noticeable.
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Old 01-14-15, 04:28 PM
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There should be plenty of Shimano crank arms out there from the 90's. I had several unmatched left arms until a few months ago when. I cleared them out by donating to Recycled Cycles here in Seattle. I'd bet they still have 'em.

Recycled Cycles | Seattle's Used Bike Shop |

Regarding the BB length issue - check out Sheldon Brown's data base on BB lengths for cranks, and ask around here for an arm that fits on that length BB. There were quite a few cranks back then that took the 122.5mm BB length. You might want to post a picture of your crank on the C&V FS forum under WTB... so folks know what your referencing. I did that a few months ago with great success.

Sheldon Brown's Bottom Bracket Size Database
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Old 01-14-15, 04:35 PM
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I would measure the distance from the tip of the old damaged arm to the chain stay. Find a replacement of the same length that is close to that distance. That's all that really matters, other than appearance.
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Old 01-14-15, 05:03 PM
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OP's crank, if what described is quite the unique piece of engineering. Regardless, and if unable to locate an exact replacement, would just find a correct fit to that spindle and arm length.

Back onto the subject of that era Shimano LX, today I happened to pull out some from the junk pile. That other thread and discussion of triple gearing made me think of these 'Hollowtech' crankset. These 175mm look rough right now, but I'm thinking of stripping and brilliant polishing for a compact triple road use.


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Old 01-14-15, 05:13 PM
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As well as concerns about chainstay clearance, consider also the orientation of the square taper hole. Some brands appear as a diamond when the crank is held vertically, others appear as squares.
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Old 01-14-15, 05:37 PM
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As an alternative, you could just use you existing crankarm. The threads are only needed for removal; not an everyday occurrence. A standard 2 leg gear puller can be used to remove a crankarm.
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Old 01-14-15, 06:06 PM
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I've mixed and matched a little bit for one reason or another.

I do have to watch it a bit at my favorite used bike store that they'll sell a 175 and a 170 as a pair.

As mentioned, most cranks have the diamond orientation, but some don't. If the bottom brackets are pretty standard, then clearance shouldn't be an issue.

Personally I would avoid replacing a black crank with a silver one, or one with a fat arm with a narrow arm, but that is more aesthetics than anything else.
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Old 01-14-15, 06:16 PM
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I use a 1982 600EX right crank arm and rings with at 1994ish Sugino crank arm at the present time, however I have also used a Shimano Tri-color left arm with it as well. It really doesn't matter what is used as long as the "diamond" or "square" and length match.
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Old 01-14-15, 07:06 PM
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It really only matters to the extent that the arm matches the spindle properly.
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Old 01-16-15, 04:51 PM
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I agree with Mr. Thompson. I would have not qualms replacing an 80's or 90's era left crank arm with just about any Japanese made left hand crank arm (Sugino, SR, Shimano). I think with today's modern bikes it is much more of a problem to match up.
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Old 01-16-15, 05:50 PM
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Originally Posted by lanciat View Post
the Park crank puller simply pulled the threads right out
those all-in-one park pullers are really awful. i use a $7 wrench-force puller in combination with a regular adjustable wrench. with a little grease, it works like a charm.
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