TallRider

I purchased a nice-looking Shimano FC-6206 (600EX, XT predecessor, sometimes known as "Deerhead" crank) on eBay. After installing the crank, I noticed that the drive-side dustcap threads (also used for a crank puller) are mostly stripped. There is some threading on the crankarm-pointing side of the opening, but the threads are almost entirely stripped on the "top" side of the opening (when crankarm is pointing down).

I plan to just ride the bike for now, but removing the crank will be difficult whenever I need to do so.
I'm curious whether it's possible to re-tap the crankarm, use helicoil threads, or just pay for destructive removal and get a new one.



The first two photos above show the condition of the stripped threads (compared to the intact threads on the non-drive-side in the third photo).
Also, this 30-second video shows that I can slide a crank puller in and out without threading. (A Park Tool crank puller, apparently with higher-raised threading, cannot be pushed in and must be threaded).
https://www.youtube.com/watch?v=E2CRliUPvGc

FastJake

While the missing threads are a major bummer there are other ways to get a crank arm off. A gear puller, for example. I'd probably leave it alone. This is more than just cleaning up the threads, you would need to replace them since they look almost completely gone.

SlowJoeCrow

Depending on the state of the threads, the Bicycle Research thread chaser. Bike Tools Etc. - 1000's of bicycle tools and parts for the home mechanic! can clean it up cheaply or find a bike shop with a Stein or Cyclus repair kit that cuts an oversize extractor thread and converts your cranks to self extracting.

rmfnla

That's the kind of stuff that gives ebay it's bad reputation.

I hope you got a really good deal on it...

habilis

Gear puller to remove, helicoil to repair. Done carefully and with penetrating oil, the removal need not be destructive

dsbrantjr

Jacobs chuck wedges: https://www.jacobschuck.com/accessories/wedge-set

robert schlatte

You can remove the crank bolt and continue to ride it until it loosens up sufficiently to pull it off.

rmfnla

Are Heli-Coils available with that fine a thread..?

habilis

Good question - I don't know. The OP would have to determine the thread count and diameter of a crank extractor, then go to this chart: helicoil,helicoil insert,helicoil inserts,heli-coil,helicoil kit,helicoil tool kit ,helicoil tap,helicoil india

fietsbob

I think there is a ring that gets put in after a cutting tool makes a new set of threads to screw the ring into.

Bike shop Industry tool ..

FastJake

Of course, this will destroy the arm unless you're incredibly careful and stop immediately when you feel it loosening.

TallRider

I plan to ride it until I need to remove it, which may be a few years or a few months.
I don't think there's enough threading left for the Bicycle Research tool to work, which may be true for helicoil as well.
If I'm able to rebuild the threading somehow, I'll post here. (Or if I attempt and am unsuccessful)

rmfnla

Well, they show metric fine thread so that's a good sign...

Right, that's what a HeliCoil is...

Homebrew01

This is probably the simplest method. And not much $$

fietsbob

Heli coil is a diamond shaped wire coiled up , it's one, But not the Only thing made to do this .


you can just ride the bike without the bolt tight it will come loose by just riding it

then you can Buy a crank that is not something someone dumped on you in worse than stated condition.

Part of the gamble of Ebay ..

JohnDThompson 

The OP's crank would have used a 22mm x 1mm extractor. Alas, nothing that fine is available from the source you found. VAR, Eldi, Cyclus, and perhaps others offer kits to cut new, oversize extractor threads and supply an oversize extractor tool to work with the new threads. But these kits are not cheap. If the OP is lucky enough to be near a shop that already has one, this may be the best way to recover the crank.

rmfnla

eBay has a 100% guarantee on all purchases so there's really no gamble (and it includes shipping both ways)...

FastJake

+1

I have had to return stuff that was broken/defective out of the box. It's a bit of a hassle, but return shipping is included. On ebay the only real risk involved is as a seller to not sell broken junk, or get unlucky with an idiot buyer that doesn't get what they thought they were going to get. Because it will get returned and the seller is responsible.

WizardOfBoz

Are there oversize thread crank pullers?

Ideally, you'd use a helicoil or thread-sert (a coil of wire of diamond cross-section that is coiled with the same pitch as the original thread). You have a machinist fasten the crank arm to a plate (use the chain-ring mounting screw holes) to ensure that the hole is accurately vertical, drill out the hole very slightly, then use an oversize tap to cut threads (or single-point them in a lathe) with the same pitch as the original, but in a larger size. Then you screw in the coiled wire. The outer part of the coil engages the crank arm, and the inner part of the coil replaces your original threads - same size and everything. Different brands of coils have different methods of ensuring that they stay in place.

The upside is that you now have very durable, steel threads. the downside is that they may not make the size you need, and the weird size tap is expensive.

Dan Burkhart 

Yes. Stein and Var both make M24x1.5 taps to oversize the puller threads. I have the Stein version, and a puller to work with it.
You can also get self extractors to fit the oversize thread.

2_i 

You cannot helicoil a crank. There are indeed dedicated tool sets for rethreading, by Var, by Stein and by Cyclus. They cost more than a typical crankset and even better bike shops will rarely have any of those sets. Using a gear puller with bike cranks is quite a hassle, so for practical purposes these cranks are goners.

TallRider

I paid $65 for the crank on eBay last year. I just asked if the seller was willing to offer me a partial refund, but unless they know about the stripped threads, they could suspect I did it myself and am trying to recoup some money.
I'll ride it and see how it works, and keep it on the bike as long as I'm happy with it. The chainline is a bit too close to the frame, but with compact gearing I'll spend more time in the big ring anyway.

JohnDThompson 

Using a gear puller or Jacobs chuck remover wedges is certainly less convenient than using a real crank puller, but for a home mechanic who may only need to service the bottom bracket once a year or less, this inconvenience might not be intolerable.

fietsbob

They'd have to be special Bottoming taps because the depth to re thread is shallow.



perhaps you can get a self extracting bolt's ring thread locked in place and dont tighten the bolt more than the minimum.

I've had a self extractor ring push the threads out of the crankarm and not Budge off the spindle. .

Self extractors are probably better suited to Spline connections

2_i 

Stripping threads in cranks is a topic of its own. There was a parallel thread discussing Park Tool, with posters asking about examples of poor design. I strongly suspect that, per crank, their puller CCP-2 killed about as many cranks as it successfully pulled.