30 November, 2006

Re-Tapping Pedal Threads

Who wouldn't want a classic Stronglight or TA crankset on their Randonneur, especially if they could get it at a bargain price. Okay, some of you (Neil) wouldn't, but pretend for a minute. One way to save money on old French cranks is to buy the ones that have French pedal threads. Some cranks are rare with anything but French threads. French threaded pedals are getting hard to come by, though VO can still get them, and the price for those pedals seems to be climbing, while the prices of the cranks drop.

French pedals have 14mm x 1.25mm thread while the far more common and slightly larger English size is 9/16" x 20. It's about 10 minutes work to convert French threads to English. Most bike shops can do this, but with about $35 worth of tools you can do it yourself. You'll need a set of English pedal taps. Park, VAR, and other tool companies make these. You'll also need a tap handle and a little cutting oil (thin machine oil or kerosene will do).

First wrap a rag around the crankarm and secure it in a vice or ask a friend to hold it on a flat surface. Next, remember that there is a left hand and a right hand tap; select the one that matches the crank. Put the tap in the handle and squirt some oil on it. Thread the tap into the pedal hole. After each half turn, reverse direction for about a quarter turn. This breaks and helps clear the aluminum chips that would otherwise clog and damage the threads.

You can get an even better deal, like free, on cranks that have stripped threads. Stripped threads can usually be repaired by tapping the hole to a larger size and screwing in an insert called a helicoil.

Be sure to put a little grease on your pedal's threads before installing them. And use pedal washers so they don't damage the crank and can be easily removed later.

16 comments:

david_nj said...

The thing that sucks about the Park pedal thread taps is, they aren't tapered as much as the VARs and such. So you can't get them started in a French-threaded hole. Don't bother buying the Park taps if this is what you want to do.

Since it's only a few $ and you have someone to yell at if they screw it up, I actually recommend going to a bike shop to have this done. Not that you're taking off much material or that you're likely to blow it, but if you do you'll be pissed for sure.

I didn't know they made 9/16-20 helicoil inserts. That would be killer for one-bike guys like me, where I'm always swapping out clipped and clipless pedals.

Anonymous said...

I believe I read on Sheldon's site that you can just reef on it with an english pedal, and a french crank, and that they will find a way to live with each other. I did that to a set of nervar stars which I gave to a buddy who then rode them from paris through italy to croatia, then up to germany, and then back to paris. the cranks are still in use.
depending on the grade of crank, I say just lube the pedal up, have some time on your hands and give'r!
m burdge

Andrew Karre said...

Hmmm. I don't know if I'd ride a crank with a helicoil insert at the pedal. Broken cranks cause ugly crashes and you're removing metal from an area where there isn't a ton to begin with. There are plenty of good cranks out there. Why risk it? Unless you're talking about Herse cranks . . .

Good idea, about tapping out French threads, though. I've had it done. Friendly shop charged me a ten.

Andrew

david_nj said...

anonymous,

No way that's possible. I don't care if you're Arnold Schwarzenegger. Nope! Unless your cranks are made of solid butter or something.

Andrew,

Helicoils are rock solid. You use them all the time in aluminum engine blocks in cars. They'd actually be an improvement in alloy cranks. They work _really_ well. Je vous assure.

Chris Kulczycki said...

David,

I've used the Park taps and they are harder to start in the hole, no doubt, but they do work. You just have to push down a little as you start turning.

If anyone wants them, I can probably order a few sets of VAR taps and pedal washers.

neil m berg said...

David,
One bike. You obviously need more bicycles. Ideally, unnecessarily complicated bicycles with weird French threading that nothing mates with except old, hard to find obsolete parts, so you'll have more to occupy your time and Chris can stay in business.

Jim G said...

Why do you need two (L & R) taps -- can't you just use a standard right-hand threaded tap on the left crank arm, starting from the back side of the arm?

david_nj said...

jim g,

Consider the matter one more time. Startin' from the back or front makes no difference. Well not one heck of a lot anyway.

;-)

Jim G said...

Whoops! Got my pedals mixed up...thanks for the heads-up, and nevermind! ;)

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Pyro said...

Hi, since I found this thread on the subject, perhaps you can help me find my solution. I live in La Habra, CA with tons of bike shops around with more interest in selling me a new crankset than helping me fix the one I have.
I would love to put a helicoil in my left crank arm. I had it done to the right side, then the left side gave out... I have a 99 Gary Fisher mountain bike with a Shimano crank that I bought from a guy at a great price... the right pedal was out, and I figured that wouldn't be a problem to fix, so I got that fixed at a local aircooled VW shop where I know the owner... ha ha He used a spark plug insert. (aka Helicoil)
Now I need to fix the left side... It's a 1/2" axle, but I don't know the thread count I'm dealing with, all I know is that it's metric, and the pedal I'm using is a V8 mountain bike pedal. I know how to use taps and all that, I just need the helicoil, and the left handed tap. Thanks for any help you can offer. -Dennis (Pyro)

Anonymous said...

I believe Sheldon said that whereas a French pedal was a loose fit in an English crank, you couldn't get an English pedal into a French crank "without considerable violence." The page I was looking at didn't recommend the procedure.

Someone may have done it but they may be light and/or weak, and they still may yet hear a loud "pop" someday just before their crotch hits the top tube on a full power climb. You are preloading the cranks with a lot of stress.

Chris Kulczycki said...

Tapping means cutting new threads, not forcing the pedal into the wrong threads!

spanner48 said...

Forcing pedals in? Well, anything's possible. I did once see a new, cheapo mountain bike in a department store where, in assembling the bike, they'd managed to screw the RH pedal into the LH crank and vice versa!
Must have had an 'Andrex' shop assistant: strong and thick . . .

Josh said...

I'm planning on re tapping an old SA left crank that I stripped pulling it out. Looks like there's enough thread left to clean it up, but I hate to spend $33 bucks on a pair of 9/16' taps when I only want the 9/16' left left-hand threaded one. If anyone has one they want to sell me for a fair price shoot me an e-mail.

Anonymous said...

Very late and slightly off the original topic of thread conversion, but there seems to be a lot of knowledge here, so here goes...
I just used the Park Tool on an old Zeus 9/16 crankset. Beforehand the pedal was going on, but not easily, and having ruined a crank recently by forcing the issue I thought I would chase them. But I'm surprised how loosely the pedal now inserts after tapping. There is noticable play, and the only way to eliminate it is to tighten the pedal hard against the crank. I thought pedal and crank threads should be close enough to be reasonably self-supporting even without having to go super-tight on the pedal. Is this normal?