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Old 09-21-06, 07:41 PM   #1
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pedal helicoil

So I helped my friend get a sweet deal on a used Trek a couple days ago. Foolishly, I encouraged him to buy some pedals for it, not realizing that he would install them himself. Seems he stripped the hell out of the threads on the left crank

So, I'm wondering how hard it is to put a helicoil into a crank. I have access to a drill press, mill, reaming tools, etc. Would an LBS sell me just the insert? If not, how much do they charge for putting one in?

Failing that, does anyone have a silver 175 mm square taper left crank arm they don't need? I have several, but they're all 170 mm.

PS- loosescrews.com and ebay don't have any appropriate 175 mm arms. Any other sources?
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Old 09-21-06, 08:21 PM   #2
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From what I saw when I was looking, helicoil isnt cost effective at all. Its cheaper just to get a new crank arm. I found one from a LBS (albeit a 170). Start calling the shops, Id think at least one would have something.
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Old 09-21-06, 09:16 PM   #3
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left side is left hand thread. Do they make left hand thread heli coils for crank arm?
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Old 09-21-06, 10:11 PM   #4
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I wouldn't trust a helicoil in a crank arm. There's too much stress on the crank. bk
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Old 09-21-06, 10:20 PM   #5
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All righty, sounds like the thing to do is find a new crank arm for my friend. He thinks he may have damaged the pedal threads on the RIGHT crank too, but says that he eventually got the right pedal in straight... I'm hoping so.

I think I'm going to give him my old Bicycling Mag book, he could learn a thing or two
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Old 09-22-06, 01:52 PM   #6
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Helicoil the company sell bicycle specific kits, LH & RH thread. There are also threaded bushings made that do exactly the same thing (Cyclo, amongst others). For cheap cranks, buy a new crank. Expensive ones are worth repairing.

I'd be interested to know why anybody thinks they'd be weaker than the original threads, given the larger surface area.
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Old 09-22-06, 02:12 PM   #7
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Quote:
Originally Posted by Moxfyre
I have access to a drill press, mill, reaming tools, etc.
With access to those tools you should be able to machine your own threaded insert & press it in.
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Old 09-22-06, 03:28 PM   #8
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Quote:
Originally Posted by moxfyre
Failing that, does anyone have a silver 175 mm square taper left crank arm they don't need?
Shouldn't be that hard to find. QBP has left crank arms listed in their catalogue so any LBS should be able to order one for you. If you're not picky about getting an exact match you should be able to replace it for around $20.00 to $25.00.
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Old 09-22-06, 03:31 PM   #9
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Thanks for all the tips! I am curious about helicoils because I have some derailer threads that will need 'em in a few thousand more miles probably.

But my favorite LBS says they have a 175 mm left for $15, that should do the trick for my friend's bike.

For future reference, bikeman.com sells helicoils: http://www.bikemannetwork.com/biking/c/TLSLUBETOOLTHRD

It appears that a special, expensive tool is required to insert them. Is that correct, or is there a clumsy-but-works-okay way to do it? I'm thinking something like a ghetto headset press... would it be possible to use such an apparatus to press in a helicoil?

Last edited by moxfyre; 09-22-06 at 03:38 PM.
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Old 09-22-06, 03:35 PM   #10
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Quote:
Originally Posted by moxfyre
But my favorite LBS says they have a 175 mm left for $15, that should do the trick for my friend's bike.
Assuming you are working with a square taper crank, check out the orientation of the square hole. There's squares and there's diamonds and they don't interchange unless you want to try an innovative pedal rhythm.
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Old 09-22-06, 03:43 PM   #11
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Quote:
Originally Posted by Retro Grouch
Assuming you are working with a square taper crank, check out the orientation of the square hole. There's squares and there's diamonds and they don't interchange unless you want to try an innovative pedal rhythm.
Okay, the shop asked me "square or diamond" as well, and I had no idea what the answer was... Isn't a JIS square taper a JIS square taper, or did I totally miss something here?

Ohhh... I think I get it. If the taper is shaped wrong, the cranks won't fit pointing 180 degrees away from each other. Innovative pedal rhythm indeed
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Old 09-22-06, 03:44 PM   #12
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PS- I found this great site on how to make a "ghetto press" for helicoils. Awesome! http://www.muller.net/mullermachine/...ert/index.html
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Old 09-22-06, 03:48 PM   #13
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Quote:
Originally Posted by moxfyre
Okay, the shop asked me "square or diamond" as well, and I had no idea what the answer was... Isn't a JIS square taper a JIS square taper, or did I totally miss something here?
They're asking about the orientation of the hole relative to the crank arm.
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Old 09-22-06, 03:51 PM   #14
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Quote:
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They're asking about the orientation of the hole relative to the crank arm.
Yeah, I'm a dumbass... Hahaha. I had never even thought about this.

To me, physicist that I am, a square is a square is a square, even if I rotate it 45 degrees. Oops
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Old 09-22-06, 03:54 PM   #15
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Yeah, I'm a dumbass... Hahaha. I had never even thought about this.

To me, physicist that I am, a square is a square is a square, even if I rotate it 45 degrees. Oops
It's one of those things that nobody thinks about until they get the wrong one.
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Old 09-22-06, 04:38 PM   #16
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One of my cranks has a helicoiled pedal thread. If anything there stronger than origional. In the past I helicoiled the sparkplug threads on my motorcycle and I never had one iota of trouble with them afterwards.

Regards, Anthony
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Old 09-22-06, 04:43 PM   #17
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Quote:
Originally Posted by moxfyre
Thanks for all the tips! I am curious about helicoils because I have some derailer threads that will need 'em in a few thousand more miles probably.

But my favorite LBS says they have a 175 mm left for $15, that should do the trick for my friend's bike.

For future reference, bikeman.com sells helicoils: http://www.bikemannetwork.com/biking/c/TLSLUBETOOLTHRD

It appears that a special, expensive tool is required to insert them. Is that correct, or is there a clumsy-but-works-okay way to do it? I'm thinking something like a ghetto headset press... would it be possible to use such an apparatus to press in a helicoil?

Once you get the proper thread cut, the larger coils can be installed with a needle nose pliers in a crank arm because of the large diameter and you have access to the other side of the hole.
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Old 09-22-06, 04:45 PM   #18
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Once you get the proper thread cut, the larger coils can be installed with a needle nose pliers in a crank arm because of the large diameter and you have access to the other side of the hole.
Cool, good to know. It looks like the Eldi pedal threads need only a 5/8 tap, and rec Loctite, which is easy to come by.

I hope a reverse-threaded tap isn't needed for the left arm
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Old 09-22-06, 05:01 PM   #19
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left arm is standard thread.

You do know that to tap for a .625" coil you need a .750" tap.
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Old 09-22-06, 05:08 PM   #20
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Originally Posted by WorldWind
left arm is standard thread.

You do know that to tap for a .625" coil you need a .750" tap.

Sitting on the bike, the left pedal thread is a reverse thread.
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Old 09-22-06, 05:47 PM   #21
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Sitting on the bike, the left pedal thread is a reverse thread.
Right! The interior thread of the left-crank insert is obviously reverse threaded, but what about the EXTERIOR thread?

I gather that these inserts are supposed to be held in place with permanent red loctite, rather than simply by the threads, which suggests that it would be safe to use a standard thread. This would allow use of common-as-dirt 5/8" tap to install the insert.

From this photo, it does appear that the external threads on the insert are STANDARD threaded. Can anyone confirm this?
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Old 09-22-06, 06:10 PM   #22
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Originally Posted by moxfyre
Right! The interior thread of the left-crank insert is obviously reverse threaded, but what about the EXTERIOR thread?

I gather that these inserts are supposed to be held in place with permanent red loctite, rather than simply by the threads, which suggests that it would be safe to use a standard thread. This would allow use of common-as-dirt 5/8" tap to install the insert.

From this photo, it does appear that the external threads on the insert are STANDARD threaded. Can anyone confirm this?
The way helicoils are made you can't have inside and outside threads in different directions, there's just no way. They are a wire bent to shape.
It does not make sense to do that anyway.
You also need a helicoil inserting tool. You have to use the exact drill and the exact tap that helicoil recomends for each different size. It's usually not standard because you are repairing a standard thread, so it can't be, it has to be just a little bigger. Did you see if there is helicoil sizes on line?

Going by a photo does not mean anything, right or wrong, the photo can be from anywhere, you can't go by that.


Edit post: go here and view the video and you can see what a helicoil actually is. This probalby will tell you everything.

http://www.emhart.com/products/helicoil.asp

Last edited by 2manybikes; 09-22-06 at 06:17 PM.
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Old 09-22-06, 06:23 PM   #23
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Quote:
Originally Posted by 2manybikes
The way helicoils are made you can't have inside and outside threads in different directions, there's just no way. They are a wire bent to shape.
It does not make sense to do that anyway.
You also need a helicoil inserting tool. You have to use the exact drill and the exact tap that helicoil recomends for each different size. It's usually not standard because you are repairing a standard thread, so it can't be, it has to be just a little bigger. Did you see if there is helicoil sizes on line?
Gotcha. Good to know! From the site I linked to earlier, they show how to improvise a helicoil inserting tool with a bolt and a nut. I figured I could use an old left pedal axle as the improvised tool!

Also, the pedal thread IS a standard 9/16"x20tpi fine thread. And according to this page, the Eldi tool has 5/8" external threads. So I don't see why a standard 5/8" tap wouldn't work, at least for the right pedal!

Quote:
Originally Posted by 2manybikes
Going by a photo does not mean anything, right or wrong, the photo can be from anywhere, you can't go by that.
Yep, that's why I asked

Quote:
Originally Posted by 2manybikes
Edit post: go here and view the video and you can see what a helicoil actually is. This probalby will tell you everything.

http://www.emhart.com/products/helicoil.asp
Thanks for the link, it's very informative. As far as I can tell, the Eldi inserts are *not* as "fancy" as helicoils; they are merely bushings which have an exterior thread and an interior thread, and must be retained with red loctite.
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Old 09-26-06, 12:42 PM   #24
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This is a helicoil
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Old 09-26-06, 12:45 PM   #25
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Quote:
Originally Posted by WorldWind


This is a helicoil
Right, thanks I gather that the little tab on the helicoil serves as a retention device, so that it isn't merely held in by the external threads. With the Eldi pedal thread inserts, it's a simpler device which is just a bushing held in place by the external threads and Loctite.
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