Author Topic: cranks  (Read 7316 times)

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Offline conifir

cranks
« on: August 26, 2009, 05:00:31 pm »
my question is how do you tell when to replace your crank....
and why do i ask....
i have 2,500 miles on my original "Bontrager crank" on my trek fuel.....

Offline whittierider

Re: cranks
« Reply #1 on: August 26, 2009, 05:34:36 pm »
Even the worst bearings (like Isis type) should last longer than that, and they can be replaced without replacing the rest of the crank.  My external-bearing Bontrager crank with GXP BB has 19,000 miles on it, many of those being climbing, and is still perfectly smooth and with no slop.

Chainrings on road bikes can go many times that long if they're kept rather clean, but I know MTB ones won't.  2500 miles is not much for a bike.  Our son put on 400 last week alone.

Offline jsieber

Re: cranks
« Reply #2 on: August 26, 2009, 05:36:31 pm »
Well, the crank arms themselves are most likely in good shape but the actual chain rings might be worn or the bottom bracket might need replacing. If the chain rings are so worn that the chain is starting to skip it would be wise to replace the rear cassette, chain rings and chain all at the same time as replacing individual pieces will accelerate wear on the whole set. If your bottom bracket does not spin smoothly or makes noise it may be time for that to be replaced. Your local bike shop should be able to help determine these issues.

Offline DaveB

Re: cranks
« Reply #3 on: August 27, 2009, 09:14:26 pm »
2500 miles is still brand new for any decent crank, chainrings and bottom bracket unless the bike is ridden exclusively in harsh off-road conditions.  Are you experiencing any symptoms that indicate something is wrong?

Offline bogiesan

Re: cranks
« Reply #4 on: August 28, 2009, 12:19:54 am »
my question is how do you tell when to replace your crank....
and why do i ask....
i have 2,500 miles on my original "Bontrager crank" on my trek fuel.....

I put more than 20k on my recumbent's bottom bracket and the cranks  have 34k on them. The chainrings have been replaced three times; rear cassette twice; five chains, maybe six.

Cranks don't go bad, they get bent, destroyed, or broken.

david boise ID
I play go. I use Macintosh. Of course I ride a recumbent

Offline DaveB

Re: cranks
« Reply #5 on: August 28, 2009, 09:46:56 am »
I put more than 20k on my recumbent's bottom bracket and the cranks  have 34k on them. The chainrings have been replaced three times; rear cassette twice; five chains, maybe six.
david boise ID
I do have to ask why you changed your chainrings that often?  My experience is that under normal road use, chainrings last at least 20,000 miles and often myuch more.  I've gotten 30,000+ miles on several Shimano road cranks chainring sets and they still shifted cleanly and there was no chain skipping and, no I don't change chains all that often either.

The only truly worn out chainrings I've seen were on my son-in-laws bike.  He is a racer and very strong but it still took him 25,000 miles to wear them to the obvious replacement point.

Offline paddleboy17

Re: cranks
« Reply #6 on: August 28, 2009, 12:02:57 pm »
I used hear that you replaced the chain and cluster together, and the rings every 3rd chain.

I see drive train replacement as being a function of maintenance. 

My mountain bike is still running 8-speed, and nice clusters are getting harder to find.  I can't get 8 speed 11-32 in XTR anymore.   The next best replacement is an 8 speed 11-30 in XT.  So I have become real anal about chain cleaning and replacement.  I have a chain gage (I think it is made by Rolhoff), and I replace the chain as soon as I see sign of it starting to stretch.  My goal is to never replace my XTR cassette.  With Shimano's tendency toward designing cranks with rings riveted on instead bolted, I don't want to replace cranks either.

In the mid 90's, White Lightning was the lubricant to use.  It used to be pretty awful stuff, and the two seasons I used White Lightning, I had to replace the middle chain ring, the cassette, and the chain.  This was too expensive for me, so I went back to using T-9 as my lubricant.  Now, I only replace chains and an occasional bottom bracket cartridge.
Danno

Offline whittierider

Re: cranks
« Reply #7 on: August 28, 2009, 03:18:32 pm »
Quote
In the mid 90's, White Lightning was the lubricant to use.  It used to be pretty awful stuff, and the two seasons I used White Lightning, I had to replace the middle chain ring, the cassette, and the chain.  This was too expensive for me, so I went back to using T-9 as my lubricant.

I use paraffin & graphite to lube the chain and keep things clean, and a 9-speed chain lasts me about 20,000 miles with a lot of climbing and no cleaning except to get the goop out of it when it's brand new before the first waxing.  The paraffin is clean, and grit and sand won't stick to it and get worked in; but it's not a very good lube by itself.  That's where the graphite comes in.  When I added the graphite, suddenly my chains were lasting 20 times as long.  For an extended tour when I'm away from the stove and pie tin I use for waxing, I plan to try White Lightning shedding formula with a lot of graphite added.  It's incredible how much you can add without any significant thickening.  The graphite powder is extremely messy before it's in the wax, but not after.

Offline DaveB

Re: cranks
« Reply #8 on: August 29, 2009, 10:20:06 am »
I used hear that you replaced the chain and cluster together, and the rings every 3rd chain.
No, you change chainrings when they are worn out and not shifting properly.