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Old 02-05-12, 06:22 PM   #1
Raleigh71
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What would a compatable replacement be for this mid 1990's crank?

I have a Miyata hybrid c. mid 1990's that probably needs a new crank as it seems pretty warped. All 3 chainrings wobble by the same amount which tells me the crank is warped. The axle is fine. Back in the old days, a hammer would do the trick but this is an aluminum crank.

Current Crank:

Exage 300 LX
(Shimano FC M300)

with

Shimano Biopace SG chainrings 28/38/48.

I've looked at the compatability chart, and the cranks with the same axle dimension requirements don't seem to be available in the main stream retail places I've looked.

What's current and compatible?

Last edited by Raleigh71; 02-06-12 at 12:03 PM.
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Old 02-05-12, 06:24 PM   #2
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Biopace chainrings will "wobble" vertically. If you are seeing a vertical wobble, then you don't need a new crank. If you are seeing a lateral wobble, you will.
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Old 02-05-12, 06:26 PM   #3
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Yeah, this is a lateral wobble. Makes the derailleur setting very, very tricky.
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Old 02-05-12, 06:28 PM   #4
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Yeah, this is a lateral wobble. Makes the derailleur setting very, very tricky.
Are you sure? What part of the derailleur setting is difficult? Height? Or limit screws?
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Old 02-05-12, 06:32 PM   #5
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The chainring wobbles back and forth so it hits one side or the other of the derailleur cage. If I set it right for the large chainring, then one of the others rubs or vice versa.
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Old 02-05-12, 06:37 PM   #6
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The chainring wobbles back and forth so it hits one side or the other of the derailleur cage. If I set it right for the large chainring, then one of the others rubs or vice versa.
Well, first of all, the derailleur cage should be positioned 2-3mm above the big chainring... Your description is not making much sense...
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Old 02-05-12, 06:53 PM   #7
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The front derailleur cage is situated right where it should be on the seat tube, right above the largest chainring.

When I spin the crank the chainring hits either one side of the derailleur cage or the other it's so warped. If I get it juuuuusssssttt right smack dab in the middle for the largest chainring so it doesn't hit one side of the chainring or the other then the other chainrings hit. Comprendez?
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Old 02-05-12, 07:10 PM   #8
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so if your standing looking down from the top the rings move from side to side as you rotate the cranks right?

you need to change the bottom bracket too but if your current rings are 28/38/48 most any of the modern compact cranksets should work


The rings should appear oval rather than round that is what Biopace is all about, check this out http://www.sheldonbrown.com/biopace.html
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Old 02-05-12, 08:38 PM   #9
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so if your standing looking down from the top the rings move from side to side as you rotate the cranks right?
+1 Lots of confusion on this thread... but I'm pretty sure this is what the OP meant.

I don't wish to go searching for your crankset, but one important consideration is chainline. Old crankset arms (pre 1990s) were relatively flat. Then in the early 90s MTB chainstays got fatter, bottom bracket spindles got narrower, and the MTB cranksets as a result had/have arms that are "bent." If you try putting an 'old' crankset on a newer MTB you have to use a super long spindle so the arms don't hit the chainstays and as a result the rings are moved very far out and the chainline gets all screwed up. AFAIK, road cranks never went through this transition.

So if you can't find out what chainline you have/need, it might be worthwhile posting a picture of your current crankset so we can at least try to point you in the right direction. Or take the bike to your LBS. Do you want another triple? Compact double?
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Old 02-05-12, 08:50 PM   #10
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Are these bolted or riveted chain rings?

IF bolted, maybe they aren't seated correctly?
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Old 02-05-12, 09:55 PM   #11
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These are bolted. I'm sure it seated on the square axle shaft.

Thanks for the info!
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Old 02-05-12, 10:22 PM   #12
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I'm not talking about the axle!
The "spider" has "ledges" that the ring sits on.
If there is crud under there for some unbeknown reason, the rings won't be seated flat.

IF the rings are actually bent, you could spend a bit of time with a hammer and a couple blocks of wood and probably straighten them out.
You can also lay them on a flat surface and see where the problem actually is and WHERE to tap them.
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Old 02-06-12, 06:56 AM   #13
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Alivio 48/36/26 should fit nicely and comes in several crank lengths. It should make a good crankset for a hybrid and you can get them with or without a lexan chainguard. I've got one on my light touring bike (a 1990 Trek 700) and have been very happy with the performance.
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Old 02-06-12, 01:23 PM   #14
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Excellent info. Thanks!

This is just the sort of information I was looking for.

Another question arises: My spindle length is 122.5 according to the specs, (I haven't measured it) and this crank takes a 113 mm spindle:

http://www.ebay.com/itm/Alivio-M430-...item3cc0be528d

Do I need to mess with the bottom bracket? The crank axle ('spindle') is in good shape.
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Old 02-06-12, 01:38 PM   #15
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YES you do. Check FastJake's info in post #9

Modern cranks are flatter than cranks for when your bike was made so as you see the spindle is much shorter. if you BB has not been serviced since new it is high time to show it some love anyway.

Did you try removing the crank from the bike and taking off the rings then placing the 'spider' on a flat surface and make sure it is warped? It is doubtful but is possible the issue is the BB or the spindle itself.
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Old 02-06-12, 03:12 PM   #16
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Might not need a new BB. I'd try it with the 122.5- it would only put the chainline out an extra 4.5 mm. If the derailleur reaches, then it's all good. If not, then you can buy a shorter BB.
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Old 02-06-12, 04:13 PM   #17
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Do I need to mess with the bottom bracket? The crank axle ('spindle') is in good shape.
Yes, I'm pretty sure you will. But you can try it first. I have an 'old' crank on a 'new' MTB and I had to use a super long 123mm spindle (old one was 115 I think) to make it clear the chainstays. The chainline is so bad that I cannot use the middle ring with the biggest cog, it actually derails off onto the granny. If you're ok with bad chainline it will probably work, but the best thing to do is to get the correct spindle.

Also, your crank arms will be much further out than necessary giving you a bad Q-factor or "tread."
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Old 02-06-12, 04:17 PM   #18
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I would get a new, correct length bottom bracket. IMO the possible aggravation of having remove and install twice outweighs the possible savings of a $20 bb.
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