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39-52 crank replacement

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39-52 crank replacement

Old 12-07-19, 11:23 AM
  #1  
Strosfan5
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39-52 crank replacement

Hi all,
Owner of an old Murray mountain bike from mid 80ís.
Long story short. Purchased 4 months ago from an older couple who never used it and stored it indoors - 40$. Have 600 miles on it since mid August. Been flawless. New tires and pedals. Thatís it. Heavy as crap but been super fun to ride.

One arm on the crank finally bit the dust. Not sure where to look for a replacement. I myself am unsure if bearing size is consistent on mountain bikes and all that stuff.

any help?



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Old 12-07-19, 11:34 AM
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rosefarts
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It's a pretty common lower end set-up. The bearing is probably fine, no need to replace.

I'd bring the whole crank into the shop. Bring the pedal too just to be sure of the ​​​spindle size. They should have some, either new or in the spare parts bin. Probably $30 or less.

Do you need them to install or will you be doing that yourself? Add 15-20 bucks for installation.
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Old 12-07-19, 11:41 AM
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Doing it myself. Iíve turned a few bolts and head gaskets and such.
thanks for the info - Iíll bring the pedals in as well. Good thought.

So bearing size is pretty consistent and arm length as well I would assume.

I was all ready for 30 miles today. Thank God it happened right in front of the house.
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Old 12-07-19, 02:56 PM
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Arm length does vary a bit, but with the old in hand, you can easily match.
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Old 12-08-19, 07:47 AM
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Or go whole hog and convert it to a 3 piece cotterless crank.Probably drop at least a pound of weight.

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Old 12-08-19, 11:21 PM
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Jeff Wills
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Originally Posted by Strosfan5 View Post
Doing it myself. Iíve turned a few bolts and head gaskets and such.
thanks for the info - Iíll bring the pedals in as well. Good thought.

So bearing size is pretty consistent and arm length as well I would assume.

I was all ready for 30 miles today. Thank God it happened right in front of the house.
Bearing and thread dimensions are consistent. Don't get Schwinn parts, though, since they use a different thread.

Here's a how-to on the Park Tools site. It looks like you've made good progress without it: https://www.parktool.com/blog/repair...vice-one-piece
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Old 12-09-19, 12:04 AM
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Today I learned that even Ashtabula-type cranks can break!
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Old 12-09-19, 11:10 PM
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Jeff Wills
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Originally Posted by ThermionicScott View Post
Today I learned that even Ashtabula-type cranks can break!
A co-worker broke a similar crank in the same fashion. I pointed him to the same Park Tool as above and he managed to replace the crank himself. He's pretty handy for a pharmacist.
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