I destroyed another crank on my MTB today: It felt odd, so I checked the crank to spindle and it was solid, but it soon worsened, and I assumed it was my cheesy pedal failing - that is, until the pedal pulled out and I knew it was the crank.

- I thought precession would only tighten a pedal in a crank!

- Any ideas on what would cause the pedal to pull out of the crank?

Looks like you're in a cold environment there. I wonder if that had anything to do with it.

The crank isn't orginal fit, so it could have been wrecked before you used it, or when you installed it.

Cold environment has nothing to do with it . The pedal was not tighten into the crankarm in the first place or it was screw in wrong .But in any case the threads need be replace with a helicoil (done at your LBS ) or replace the crank .(which will cost over $100 ).Might be able to have the threads re tap from the backside of the arm.

Thanks Ben, but I sorta doubt it because I've ridden plenty of times in weather 40 or 50 deg colder without encountering anything like this.

I consider that a possibility jimc101 - The crank came from an old Schwinn le Tour, and conceivably some PO had installed a left side pedal in it at some time. The odd thing is that I put about 100 hard miles on it before this happened -I would have thought it would have failed sooner in that case.

That's 2 votes for pre-existing damage.
I have some reservations, but maybe that's it.

I don't think there is enough meat left for a helicoil, so I'll just replace the crank with one from my stash. (I just don't want to have to deal with it again. The bike is used hard but I'd like to get at least one season out of a crank and bb.)

Your bike is a 1995 Marin Pine Mountain, which from the factory had White Industries branded Sugino cranks, the pedal looks very similar to the original which came with the bike. For the Schwinn crank, it could have been the 100 miles which did it in.

Your identification skills are dead-on. It is a '95 Pine Mountain!

The pedals are not original though - they're cheapies I bought from Amazon, and I would have expected that those would have failed first, but I think you're right about the 100 miles on the le Tour crank. - If the threads were compromised to begin with that is. I've just never has this happen quite like this before.
Thanks for your input.

BTW - These pedals have outlasted three cranks and two bottom brackets on this bike. ( Maybe they're not so cheesy after all!)

I figured that was doubtful.

Just the reverse on pedals. If the rider is locked into the pedals and the pedal bearing fails, then the normal pedalling action will unscrew the pedal from the crank. If the threads were reversed, then the failed pedal bearing would break the rider's ankle.

Assuming that the pedal thread was the proper size and screwed in properly into the crank, the most plausible answer to "how did it happen" is bad pedal bearings. If the pedal will not spin freely, then continued pedalling will loosen the pedal from the crank. Perhaps water infiltrated the bearing surface and froze, to cause the friction.

I was a volunteer mechanic on NYC's Summer Street, where Park Avenue is closed to cars on the first three Saturdays in August. There are a lot of bikes in need of serious maintenance along the route. I saw more than my share of loose pedals this past year. I traced the cause to tight pedals with bushing bearings. I suggested the rider purchase new pedals before they do serious damage to their crank. One woman did not go to a bike shop but returned the early the next Saturday with new cranks she had purchased on ebay. The bearings on the new pedals were just as tight.

Threads are obviously gone now. I am in the prior damage group on this one.

To use a helicoil, the old treads (what left of them ) is drill out and the helicoil is then put into the "new " hole and held in place with a heavy duty threadlock .

There is also a non coil type pedal insert, a tube threaded on both sides,
but the process to tap the larger threads in , and install the repair insert, is similar.

[QUOTE=auchencrow;13645334]Your identification skills are dead-on. It is a '95 Pine Mountain!
[/QUOTE

Had one since '95

For the bike lasting, surprised you still have so many orginal parts, the wheels on mine didn't last too long, Mavic 230's on the rear split at the sleve joint, and the front spokes decided to snap, the seatpost un-bonded itself, most ofther parts got replaced / upgraded over the years, the frame is still going with only the rear hub and crank arms being orginal now.

SBinNYC - Some very enlightening information here - When it comes to pedals, I had the precession thing all wrong and I'll be checking my pedals more closely now.
Thank you for that.

I've already swapped out the crank, but I'll look into this before recycling the old crank. It's beyond helicoiling I think, but this might be useful considering the rate at which I've been burning through drive-train parts on this bike. Thanks fietsbob.

Proactive measures? What are those? This is my winter beater, Thrifty Bill!

[QUOTE=jimc101;13645625]
jimc101 -
I've only had it two seasons but the snow, salt, and rough roads are taking a toll on the drivetrain parts.

• I destroyed the 1st bottom bracket spindle that had probably been there originally, and then a new cartridge bb as well. (No more cartridges for me)
• Popped a half dozen rear wheel spoke nipples so I re-laced the thing with all brass. (No problems since).
• The first crank was fried along with that first spindle, and you saw what I did to the second one.
• The canti brakes lasted half a season - I installed new Tektro's, with Kool stops on the rear.
• The front DR gave up (I'm running it as a 7 speed).

Amazingly, the grip shift still works (when the cable is not immobilized by re-freeze)
-and the fork (original optional equipment I think) hardly fades at all, even in extreme cold. Most guys eschew front suspension for winter rides, but I am glad I have it, having bumped up against a few snow covered curbs.

All in all though I think it is a terrific mountain bike. I do my best to keep it lubed and I douse the frame now and then with T-9 to avert rust. I think the frame at least will outlast me.

I would inspect crank arm threads prior to installing pedals. Those are obviously stripped out now. I wonder what they looked like 100 miles ago. I start pedals by hand (no wrench) to eliminate possible cross threading. Realize that pedals have strong steel threads, while your crankarm is soft aluminum threads. Crank arm loses any argument there. So I am pretty careful here.

Typically, I will turn it at least a couple of revolutions or more, before I put a wrench on it. I do the same thing with cup and spindle bottom brackets. Its really easy to get threads out of alignment, at least for me. I lose the feel for the threading when using a wrench.

I use anti sieze compound on both, probably all kinds of theories there, not sure mine is any better than anyone elses. I use similar cheap platform pedals. Grease on most stuff, anti sieze on bb threads, pedal threads, and freewheel hub threads.


Just about every crank I use is used, along with about half the pedals I use (all the pedals I have on keeper bikes are used, as I like the old tricolor 600 pedals).

+1 Durability of cartridge bb is low compared to the old cup and spindle design.

I wouldn't bother with a helicoil on this one. Used MTB cranks are cheap (often come in the form of a complete bike, ie., donor). I would keep the chainrings.

Hi Thrifty Bill - I am of the same (hand-start everything) persuasion. I use grease instead of anti-seize, and I really don't think I've ever encountered any stuck component that had one or the other.

I am running road cranks on the MTB since that's what I typically have around. As I recall the inner ring was the same as the big chain-wheel on the old MTB crank so it works out.

I tend to save the better road cranksets for road builds. I will also use the larger two rings on MTB cranks, as a thrifty guy road compact, that's what I have on the Katakura right now. I would be tempted to use a cheap riveted steel mtb crankset on that bike given the service, although the rings would be smaller than that road crank. Or even one of those ugly lower end road cranksets with the steel chain rings.

Interesting. I'll have to tell my BB-6500 Octalink bottom bracket that it should be dead way before now.

Seriously, I've had excellent service from Shimano and Campy sealed cartridge bbs. The Octalink mentioned above has 32,300 miles on it and is still smooth and free of any play. It is the longest lived (so far) but I've gotten over 30,000 miles on two UN-XX square taper bottom brackets and retired them for crank upgrades, not because they failed in service and have 19,000 miles and counting on a Campy Chorus square taper bb.

No, you had precession correct. Precession of the pedal axle threads in the crank will tend to tighten as a result of your pedaling action. It was a definite problem when I converted our tandem to a 'kid-back' type and used a child crankset flipped so the chainring was on the left side. As a result, the left pedal was right-hand thread and vice versa which resulted in a strong tendency for the pedals to loosen up due to precession.

OTOH, bearing friction in the pedals using the normal left pedal = left-hand thread system will tend to loosen the pedal. With good, properly working pedals this is usually a smaller effect than that of precession. But apparently not with the cheap bushing-bearing pedals seen by SBinNYC.

The kit to ream, tap and install the inserts is not cheap, but perhaps your LBS may have one already?

https://www.universalcycles.com/shopp...1&category=214

Just based on my unscientific experience. In buying and selling several hundred used bikes, out of the bikes I have acquired with spindle and cup bb, 5% or less are worn out. Meanwhile, when I find a bike with a cartridge bb, 75% or more are shot. Most of the ones I find are Shimano UN-xx square taper. No Campy cartridge bbs, an occasional Octalink.