Specialized cross trail crank arm problem

I have two Specialized cross trail bikes, one elite and one carbon fiber. On the elite I lost the nut on the left side of the crank arm attaching it to the lower bracket axle after only about 300 miles of riding the bike. The dealer replaced it under warranty. After logging about 400 more miles I recently lost it on a ride from Key Largo to Key West. We were about 12 miles from Key West when the left pedal felt sloppy and I realized I had lost the nut again. I had to carefully ride the last 12 miles w/o the nut. The nut is atypical so is a special order. A Specialized dealer in Key West said that after a second occurance I should ask Specialized to replace the entire crankset. I have a friend who also owns the same bike and has had the same problem multiple times. He carries an extra nut and wrench. Has anyone else had this problem and if so what has been the response by Specialized?

 

I believe that, once again, the dealer should handle the replacement for you.

 

That's good advice, but if this is a chronic and common problem, you need to look at how the nut is being installed. Typically, manufacturers recommend greasing the threads (which appears to be the case in your pic), but that's apparently not working well. I suggest cleaning the threads in the axle completely and installing the new nut with Loctitle 222 (purple) or 242 (blue). That should prevent it from loosening again, but will allow disassembly when necessary.

 

Greasing threads on a crank bolt? That seems odd on a component that is under constant stress.

I would suggest a Loctite that seems very difficult to get - it is blue but is not the standard Loctite. You put it in a straight line across the threads and allow it to dry. If forms a rubbery layer. This does not lock the threads but adds resistance to movement and you don't have to worry about getting the bolt off if you need to service the bearings. I don't have a number on it and have been told that in general it is only purchased by factories.

 

The common Loctite liquid products are designed to cure only in the absence of air. However, they make industrial products that can be applied to fasteners and it will dry in place, but still function when the fasteners are used, which is what I think Tom is referring to. I see this stuff all the time on cleat screws, crank bolts, BB cups and other parts. There's also a blue Loctite 248 stick that looks like an oversize Chapstick and has a similar soft-waxy consistency. It can be handy at times.

The 242 formula is also sold under a bunch of other brands and may well be made by other companies, since the patent must have expired decades ago. I've used other brands and they all seem to be the same stuff.

On large, fine-threaded fasteners, you don't necessarily need the medium strength 242/248 blue products. The lower strength 222 purple formula will do the job and be easier to disassemble.

I've also seen a green product on some BB cups, but I have no idea what it is or who makes it.

 

IF the time comes when Specialized no longer wants to "repair" the crankarm & the OP has to pony up for the repair, then I recommend that he considers getting a BB adapter & install a Shimano Hollowtech II crankset or Shimano-compatible/FSA (MegaExo) equivalent.

IMO, the installation and (especially) the maintenance of Hollowtech II & MegaExo cranks is pretty foolproof.

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FYI. I returned to our Florida home two weeks ago and picked up my bike at the dealer. Specialized replaced the entire crankset at no charge.