warning helicoil blues

Hi folks I wanted you to be aware of a repair mishap I went through that may have caused some serious pain that I wouldn't want anyone to go through. Over a year ago I cross thread my crank arms on two occasions ( I know I'm a dork-thread them with your hand first). the bike in question is my warm weather bike. I sustained a foot injury last year that was a mystery but mostly recovered. then this spring after a tour I had left knee soreness .I took time off and then built up my mileage to 160 only to suffer right knee soreness . Frustrated I went to Turin for a RAD fit. Only the fitting didn't happen because one of my pedals seemed to be a quarter of an inch farther out than the other. The mechanic and the sales person -fitness expert couldn't figure out this discrepancy  . I had a guy who works for SRAM look at my bike and he said helicoiling was the problem. Basically he said that no mechanic can hand tap a crank arm perfectly perpendicular. A milling machine is required. So I have purchased a new crank set. A hard lesson learned that I wanted to share with the Chainlink.

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Permalink Reply by Michael Perz on July 21, 2010 at 7:31am
Basically he said that no mechanic can hand tap a crank arm perfectly perpendicular.

Baloney. Your mechanic should be able to tap threads perfectly square to the bore with his eyes closed. When used properly, taps are self-correcting. You should find a better mechanic.

Oh, and...

I had a guy who works for SRAM look at my bike and he said helicoiling was the problem.

Was his solution to purchase a shiny, new SRAM crankset by any chance?
Permalink Reply by Doug Haynes on July 21, 2010 at 7:38am
The guy who works at SRAM is off base if your problem that the pedal is .250 farther out then the other.

If the hole had not been drilled and tapped straight you would have the pedal at an angle compared to the other one not farther out or in and I highly doubt you could have enough deflection in the pedal to be .250 off and not notice the angle when you ride.

Is the arm that had a thread insert put into it the one that is to far out or to far in? To me it sounds more like the insert is not in far enough on one side and causing the threads to bottom earlier then intended.

As for not being able to get the hole straight enough in the arm to not have a the guy who works at SRAM is not a very skilled mechanic; I have hand drilled, tapped and installed inserts by hand numerous times in the past on stuff that requires as much, if not more, precision then the crank arm and had no issue.
Permalink Reply by Craig S. on July 21, 2010 at 10:03am
How in the hell can this guy work for SRAM?? I had to tap the right crank arm on my Big Red Fuji that I ride on Marauders back when I was 15. Haven't had a problem with it in 30 years. If I could do it as a 15 year old and the SRAM dude, can't, perhaps he needs to be asking if I want Biggee fries with that....
Permalink Reply by Mike Bullis 5.5-6.5 miles on July 21, 2010 at 10:18am
I was gonna call Bullshit on the SRAM guy, too, but I was beat to it.

I've had dealings with SRAM re:my S7 hub and it wasn't pretty.
Permalink Reply by Vondo on July 21, 2010 at 10:35am
I have never tapped any threads in my life, but even I can reason that if the tap wasn't square, the pedal would be slanted/not horizontal, not farther out or in.

One question though, how is it that taps are self correcting? Not trying to be sarcastic, just wondering.

Thanks!

Michael Perz said:
Basically he said that no mechanic can hand tap a crank arm perfectly perpendicular.

Baloney. Your mechanic should be able to tap threads perfectly square to the bore with his eyes closed. When used properly, taps are self-correcting. You should find a better mechanic.

Oh, and...

I had a guy who works for SRAM look at my bike and he said helicoiling was the problem.

Was his solution to purchase a shiny, new SRAM crankset by any chance?
Permalink Reply by Doug Haynes on July 21, 2010 at 11:32am
I didn't even realize Michel Perz posted in sync with me...

I would not say 'self correcting' but taps have a taper to them which, when the tap is used correctly, will generally work to keep the tap square to the hole you are taping. To get a tap to go really haywire to the bore you have to really force it in there.

Now, getting the hole drilled straight can be a bit of a challenge depending on how chewed up things are; that is where the skill comes in but if you take your time, use quality drill bits, take the hole up in steps you should be able to get the hole straight enough be be acceptable in 99% of all applications.

If I can install threaded inserts straight enough for head bolts in a race motor with a hand drill I see no reason a skilled bike mechanic could not get the crank arm right.

SRAM guy = mechanic FAIL.

Vando said:
I have never tapped any threads in my life, but even I can reason that if the tap wasn't square, the pedal would be slanted/not horizontal, not farther out or in.

One question though, how is it that taps are self correcting? Not trying to be sarcastic, just wondering.

Thanks!

Michael Perz said:
Basically he said that no mechanic can hand tap a crank arm perfectly perpendicular.

Baloney. Your mechanic should be able to tap threads perfectly square to the bore with his eyes closed. When used properly, taps are self-correcting. You should find a better mechanic.

Oh, and...

I had a guy who works for SRAM look at my bike and he said helicoiling was the problem.

Was his solution to purchase a shiny, new SRAM crankset by any chance?
Permalink Reply by Michael Perz on July 21, 2010 at 1:22pm
DUG, that's exactly what I meant. You have to really force a tap to get it to cut crooked. When you work slowly and frequently back the tap out to break the chip as necessary the taper will follow the path of least resistance. It will cut perfectly square.

After revisiting Jonathan's original post though, I'm not sure that's what happened. It sounds like the threads were cut incomplete rather than crooked. Threads for Helicoils must be cut until the tap can be turned freely by hand. It sounds like the mechanic didn't make it past the tap's taper causing the the pedal spindle to bind and not thread in completely. Either that or he didn't break off the installation tab afterward. If the latter is the case, it can still be easily corrected.
Permalink Reply by Michael Perz on July 21, 2010 at 1:34pm
Aaarrrggghhh!!! The more I think about it, the more I become convinced that the guy forgot to (or didn't know he had to) break off the tab. Remove your pedal and look inside the bore. If you see a piece of the Helicoil at the bottom jutting toward the center, that would be your culprit. It is crimped at the base and should easily snap off by resting the tip of a flat blade screwdriver against it and giving it a light whack.
Permalink Reply by Doug Haynes on July 21, 2010 at 2:06pm
I'm putting my money on the insert not being installed far enough.

We need to get the crank arms for science.



Michael Perz said:
Aaarrrggghhh!!! The more I think about it, the more I become convinced that the guy forgot to (or didn't know he had to) break off the tab. Remove your pedal and look inside the bore. If you see a piece of the Helicoil at the bottom jutting toward the center, that would be your culprit. It is crimped at the base and should easily snap off by resting the tip of a flat blade screwdriver against it and giving it a light whack.
Permalink Reply by jonathan on July 21, 2010 at 3:35pm
I didn't say the SRAM GUY DID THE REPAIR. You could be right about the tap depth. two different shops did the repairs.The Pony shop did the first helicoil. I was on the ridding near Performance when the second crank unraveled so I just dropped the bike off with them. Johnny Sprockets had sold me the crank set originally and offered me a new one for 230. I walked away from that offer and found a new giga pipe truvativ crank set on E-bay for 87 bucks


notoriousDUG said:
I'm putting my money on the insert not being installed far enough.

We need to get the crank arms for science.



Michael Perz said:
Aaarrrggghhh!!! The more I think about it, the more I become convinced that the guy forgot to (or didn't know he had to) break off the tab. Remove your pedal and look inside the bore. If you see a piece of the Helicoil at the bottom jutting toward the center, that would be your culprit. It is crimped at the base and should easily snap off by resting the tip of a flat blade screwdriver against it and giving it a light whack.
Permalink Reply by jonathan on July 21, 2010 at 3:36pm
I didn't say the SRAM GUY DID THE REPAIR. You could be right about the tap depth. two different shops did the repairs.The Pony shop did the first helicoil. I was on the ridding near Performance when the second crank unraveled so I just dropped the bike off with them. Johnny Sprockets had sold me the crank set originally and offered me a new one for 230. I walked away from that offer and found a new giga pipe truvativ crank set on E-bay for 87 bucks
Permalink Reply by Michael Perz on July 21, 2010 at 4:54pm
I don't think anyone here assumed that the SRAM guy was who had repaired it. You made it clear in your original post that someone else did the repair and that the sales guy simply commented on it. I just found his comment regarding Helicoils to be erroneous and completely uninformed based on my own experience with them. I can't really fault him for it though considering that his job is simply to sell people new parts.

An important thing to know about Helicoils is that when installed properly in aluminum they are stronger than the original threads. The bottom line is that whoever installed it for you should have been able to successfully do it by hand and that the SRAM sales guy gave you bad information by claiming otherwise. If you don't believe me, then call or visit just about any machine shop and ask how they do it.

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