Stripped threads on pedal crank arm
 

The order time and cost for a replacement arm has me thinking heliocoil repair. I called every LBS close to me and most don't know about the heli-coil repair (had to explain it the 3 different shops) and none of them do it. They all offer to sell me a replacement arm but all would have to order, which takes time and something I could do myself.

I have been looking at the eldi and unior kits. I hate having to pay the upfront cost for two taps, and while the inserts are not cheap by heli-coil standards, they are still a bargain when comparing with arm replacement. It looks like the kit, at ~$125.00, will fix six sets of pedals (however, most are seem to strip on the left side). Additional insert kits run ~ $12.00 - 20.00 each pair, depending on the source (if you could ever use that many).

So to my questions: Does anybody know if the eldi and unior inserts are cross compatible? Do you recommend one brand over the other? Finally, is there anyway one could rent these taps or coop share them based on some kind of deposit? The upfront cost of the tools along with inserts works out to ~ $20.00 per arm set over six repairs, I just don't know if I would ever use them again after the initial repair-which makes that a $125,00 repair. I would be glad to give someone $100.00 for one left and right insert plus use of taps if they would refund me, say, $65.00 or $70.00 bucks once I returned the taps in good condition. Or maybe I should buy the set and make the same offer to others with this same problem. Just thinking.

Any insight would be appreciated.


thanks,

'bob

the problem with helicoil is you have to drill over-sized in the crank arm to install the helicoil.
You won't have much cross section left and risk a fatigue failure.
With the risk, the cost of this major esoteric repair is not worth it compared to replacing the crank arm, especially if you can replace a single arm to do it.

Check ebay. Somebody may be selling your crank used, and used contemporary cranks don't sell for much on ebay.

When I was wanting to change gearing on my daughter's IGH, -2T front, +2t rear, I upgraded her crank for the same cost as a chainring.

Rudebob,

I agree with Bulldog. After you drill that hole out there will be very little serious metal left to handle a lot of torque. Is it worth a try? Yeah, maybe, but it would be a serious downer to snap a pedal off from the crank arm in the middle of a longish ride. Could have some health consequences to.

If it were me, I'd get a new arm and be done with it.

On your first note, most bike shops today don't do what I call "real" bike repairs. They are assembly shops that replace parts. The few that do know what a Helicoil is probably haven't done many recently anyway because, well, everyone just replaces parts now not fix them.

To give you an idea on how well Helicoils can work, many years ago I stripped out a cantilever brake mount boss on a brand new Specialized shock fork. I had worked in shops for years and could torque bolts down but this one just never tightened up. Anyway, took it to a shop that did good work and they fixed it with a Helicoil. That was done back in the early 1990's and that bike is still ridden weekly and the brake boss hasn't failed.

I see you're in Phoenix. Go to Landis Cyclery in Scottsdale (Near intersection of Scottsdale and Shea). Those guys do good work (best shop in town I think) and probably will have the expertise to repair with a Helicoil.


-

What is the crank that was stripped? Side? Length? Model?

Some new crank arms can be quite cheap. Check your local bike co-op if you have one.

How badly is it stripped? Some people have suggested possible threading a pedal in from the back side to repair some threads. .

I haven't done the crank helicoil, but I've seen Tandem cranks that have been helicoiled, and look very good. I did something else a long time ago, maybe a spark plug, and it lasted for as long as I needed it.

I do have standard 9/16 pedal taps around here, but not helicoil taps which would have to be larger.

The thread pitch on the helicoil taps should be dictated by the threads on the pedals at 20 tpi... but I guess not.

Var Taps: 5/8 x 24 tpi
https://www.vartools.com/en/9-16-x20...t-var-p396.php

Unior Taps: 5/8 x 24 tpi
Unior Pedal Tap - 5/8" x 24, Right
Unior Pedal Tap 5/8" X 24 Left
Unior Pedal Tap and Thread Insert Set 9/16"

So, VAR and UNIOR should be cross compatible. I'm not seeing EDI.

It looks like Niagara sells individuals.

Tap handles are common, and any machinist or machine shop should have lots of them.

Oh... if you're doing the right side, you might get away with a 5/8 x 24 tap (without the reamer).
https://www.amazon.com/HSS-Right-Han.../dp/B008B1NIRW

It looks like 5/8 - 24 Left taps are also available if you hunt for them.
http://www.ebay.com/itm/5-8-24-GH3-H...-/222050565365

A taper tap might be a little better, but the plug tap should work.

Without the built in reamer, the machine taps will need the holes pre-drilled.

I have never seen nor heard of a failure on a Helicoil repair. The typical aluminum crank arm has plenty of metal left, and the concern about removal of some of it ignores the fact that the removed material replaced by the steel insert. A Helicoil is not a good solution if an affordable replacement crank is available, but crank arm failure is not a concern.

+1. A crank with a correctly installed Helicoil is better and stronger than new.

There's a significant difference between the ELDI/Union system (they're the same, or used to be), and a helicoil type insert. The solid bushing design calls for more hole enlargement than a spring which only requires the thread height (1/2 height per side).

There's little, and based on plenty of experience in use, no material loss of crank arm strength. I suspect a co-op would have one or the another system since they deal with this kind of stuff every day. Also, any decent shop should have one if they do repairs to any significant degree. I sold many dozens of these kits when I was a wholesaler, and I believe QBP still has them for sale.

FWIW - the right side is a stock item since it was a popular spark plug thread. BITD - the maker was willing to wind LH coils for me, but only if I committed to 100 taps, which I did. It might be that if nobody will commit to the LH taps, that version may no longer be made.

If there's no co-op near you, look for an older shop who's mechanics actually fix, rather than simply replace parts. There's no logical need for an individual to buy the tools because it would never pay for itself.

I take it you want to do the install yourself ? If you have never done it , go slow . You will not be able to drill the hole with a hand held drill motor a drill press with a low speed will work a mill is suggested . Have you tried to get a hold of a shop that does that type of thing ?

The actual kits appear to be designed to both ream and tap by hand.

If one buys a machinist tap, then the hole will have to be drilled before tapping.

That sounds good, easypeasy . I'm not failure with that kit . I'll keep it in mind , thanks .

Are the threads completely stripped or you just can't get the threads started? LBS should have a 9/16 l/r tap that can be used to clean up the threads.... do it from the backside of the arm as mentioned for the best result.
If threads are gone the alternatives have already been given to you. I like Timesert over Helicoil, but both will work.
ben

This is probably good advice.

I ran into all kinds of resistance when trying to get a JIS crown race seat on a Japanese fork milled to ISO. Mechanics at various LBS accused me of trying to do things jackass, not knowing what I was talking about, can't be done and I have to take it to a machine shop, etc.

I finally found an older mechanic who used to build frames and he had all the tools the other guys said didn't exist hanging right on his wall.

So yeah, I would be patient, and look for that older mechanic or frame builder. Don't get discouraged.


-Tim-

When I use a helicoil to fix a stripped bolt or sparkplug in a car, I just have to get a new set of threads (the helicoil itself) in the right spot with enough strength so the old bolt or plug will work the same as before, as in bolting an exhaust manifold flange to the engine block. If the angle is off a bit it's probably ok.

With a pedal, the helicoil has to be installed so the pedal points in the exact same direction relative to the crank arm as it did before, or that pedal will feel bent when you ride the bike. This makes helicoil-ing a pedal a very difficult project vs fixing a stripped bolt on a '97 Dodge. I have no doubt it would be strong enough. A hand drill and a regular bit is going to take some luck to get the hole aimed just right.

Check with AutoZone, Advance, etc. They may have kits you can rent. I would just look for an arm on fleabay. But if you're the adventurous type then go for it.

I'd also look into an out of town shop like yellow jersey who most likely can do and shipping a crank arm isn't very expensive.

Yellow Jersey, Ltd., Arlington WI USA Everything Cycling Since 1 April, 1971!

+1 Helicoils are commonly used in aerospace applications, not as repairs but integral to the part to provide stronger threads in aluminum, magnesium, etc. parts than the base metal can offer.

9/16 x 20 tpi is pretty bike specific, I think.

I'm seeing a common spark plug size is 14mm x 1.25m But, that would be close, but perfect.

Actually, it looks like the spark plug helicoils will do FRENCH threads if you want :thumb: The helicoils are a hardened steel, and you shouldn't mess with mismatched threads.

...+1 to all of this. If you've ever done one, you see right away that these are not helicoils, but rather stamped sheet metal of some sort. with inner and outer threads provided courtesy of the forming process, not wound steel like helicoils.

There used to be a manufacturer for helicoil system (both R and LH) for this use, but they long since stopped making and selling them.

The Eldi and the Unior appear to me to be identical. I have a set myself, and we bought one for the bike co-op here, but I'm not 100% certain there's anyone who knows where it is or how to use it now. The threadserts are not cheap, and a lot of the cranks that come in there stripped are not worth the cost of the threadsert to repair them.

On the issue of getting them in straight, the tools ate a tapered reamer combined with a tap, so it's not all that difficult to get them in straight if you pay attention and do the repair off the bike, in a vise.


I would not invest in a set yourself unless you plan on doing this olde bike repair thing for quite a while. But if you really can't find anyone with a set in your greater Metro area, PM me in a couple of months when it warms up a little bit and I'll see if I can find the set over at the co-op. But it means you're on the hook for the cost of the threadsert (5 to 8 bucks, IIRC) and the postage roundtrip. Plus the time lost, so you ought to look some more in your local metro area.

...BTW, the best thing about having the tools yourself is that you can get some pretty nice older cranksets that are considered useless by other people for bargain prices, and then use them yourself. Some of the Campy, Stronglight, Ofmega, Dura Ace cranks are nice things to get and use on the cheap.

If you decide to go this route, I can't recommend one brand over the other, and would not be surprised if they are both made in the same facility. The reamer/tap combo tools are a slick piece of machining.

Thanks for all the replies. FWIW I have tried to locate a used replacement via all the usual suspects-ebay, craigslist, etc. The only one I found that will work so far is not an exact match and somewhat rough-not to mention that good of a deal. I don't want to sit around waiting too long for a used one to come along as this is a new-to-me MTB that I am itching to get out on. Plus, I am wasting prime time desert riding weather.

I am not concerned about this repair compromising the integrity of the arm. There is plenty of cross sectional mass and the new threaded bore size only increases the diameter by .062". I perform failure investigations on metallic parts routinely (I work in a metallurgical laboratory), so I know a suspect design issue when I see one.

As an experiment, I may try to create a "fractional ownership" on the repair kit. Buy it for $125.00 (which includes six sets of threaded insert bushings). Use it to make my repair and then list it on ebay for $20.00 - $25.00 less than new (but now including only 5 sets of bushings). Let the next guy do the same thing at a further reduced cost, and so on. I would jump on this personally if somebody did same thing. Do you think this would sell?

Thanks again,

'bob

It would be hard to make your money back since it would be difficult for people to find you that might need the repair. I pondered the same thing when I had a pedal strip out. I just bent over and handed the LBS my money. If you dont have anybody semi-local to do it for you, PM me and I will send you the info for my shop that did the job here in OH.

-SP

You are correct. I have some here that are 26 tpi outside and 20 tpi inside. been a while since I've done such a repair, but the reamer/tap set I have is a Cyclus brand.

Bob
what did you do ? did you get the set and then pass it on with 1 less insert? I thought that was a good idea! I found some inserts (wasn't easy at this time) but I am not sure what to do about the tap. the cranks I have are 165mm not easy to find.
thanks!

That was a while and 2 mountain bikes ago but I did end up finding a good used crank arm for about $50 bucks on ebay.

thanks for answering Bob!