The Golden Wrench

A blog about bicycle repair and maintenance by the mechanics at Freewheel Bike.

Sunday, May 30, 2010

When Life Gives You Lemons, Use a Helicoil

Soft metals such as aluminum and magnesium are touchy about torque. If you get too frisky with a bolt in an aluminum part, the part will often say "Oh, I see, is that how it's going to be?" and barf up all its threads. Then you have yourself a fancy aluminum paperweight or wind chime. Sometimes it's no big deal: if I stripped out the bolt hole on the hardware of a Kalloy seat post, I would fire the whole thing into the recycling bin with a Spaniard's flair. Fox forks, on the other hand, are generally worth saving.

Whether it was zeal for the fatherland, anabolic steroids, or a poorly-timed sneeze at the end of the torque wrench's range that caused the customer to strip the threads out of the brake post, he was sad. We consoled him and gave him options: He could a) jam his foot into the crown of the fork when he wants to stop [not great]; b) bring a piece of broomstick to shove into the spokes when he wants to stop [not great either, and no modulation to speak of]; c) get a dragster parachute for his hydration pack [time-consuming]; d) drill a hole in his brake arch and mount a side-pull caliper BMX brake [he considered it, but all we had were gold ones from 1983]; or e) use a Heli-coil insert to have brand spanky-new threads in the existing place.

Oh boy oh boy oh boy, do I get excited to deploy new-fangled technologies! I guess new-fangled is a bit strong in the adjective department: they were developed in 1938. They're stainless steel, stronger than the original threads by a longshot, and used all over the aerospace industry! Why, Boeing endorses them for crying out loud!

Yes, Boeing. The people who make the airplanes in which you fly south to visit Grandma. Boeing employs klutzes and louts who can't operate torque wrenches properly:

Announcer: "Welcome to the secret test facilities for Boeing, where two top aerospace technicians are putting the finishing touches on a brand new prototype for a passenger aircraft, scheduled for its first flight tomorrow morning. Here, working on the hydraulic control mechanisms is Brad, age 42, a 1994 MIT grad with a degree in materials analysis and a minor in Baltic Satirical Literature, father of two and a half, scratch golfer at the local putt-putt emporium, and a real hound for quality used furniture. Assisting Brad is Floyd, age 46, who is several pounds too heavy for his jumpsuit, has a degree from the University of Texas in metallurgy with a hand-to-hand combat minor, owns four Boston Terriers each named Carlos to avoid confusion, and has written several noteworthy sonatas for the accordion. We join them now in progress as they install something expensive."

Aerospace Technician #1: "Blast it, Floyd, I can't find my crescent wrench: can I borrow yours?"

Aerospace Technician #2: "I thought you were using it to get pigeons outta the rafters this mornin.' You looked up there?" [gesticulates vaguely towards the roof of the hanger, some fifty feet above their heads]

Aerospace Technician #1: "Oh, yeah. I mean, naw, not yet." [gazes at the roof intently for nearly two minutes] "Huh. Ain't seein' it. OK if I borrow yours then?"

Aerospace Technician #2: "Well, the best one I got is this here one that says 'Brad' on it. Just a coincidence, mind you now, that it's called 'Brad.' All my tools got names, they're kinda like friends in a way." [tosses adjustable wrench toward Brad, who fumbles it, dropping it onto something expensive with a hollow 'clang' and a few muffled oaths as he fishes it out of the compartment]

Aerospace Technician #1: "Yeah, I here ya." [Looks closely at adjustable wrench] Say, this here's not a metric crescent wrench: you think it'll still work?"

Aerospace Technician #2: "Can't hurt to try. How come you don't use that fancy 'lectric torque wrench they give us?"

Aerospace Technician #1:"Aww, corn shucks. I took that thing home for the sport of my younguns, who are inclined toward things that beep and light up. You don't need a torque wrench when you been doing this as long as I..." *CRACK* [The color drains from Brad's face as he backs the fastener out of the hole, only to discover that the threads came with it. Beginning to perspire, he glances furtively about the facility to see if a supervisor was privy to the destruction.]

"Uh oh, Floyd, better grab a Heli-Coil."

[Lights dim, big-band music begins blaring from somewhere]

Man with Top Hat: [Steps out from behind something expensive, Crooning]

Broke something expensive, and you don't know what to do?
Too obvious for duct tape, or too big for Krazy Glue?
Stripped the threads from something that is worth more than your life?
Is your supervisor marching toward you with a butcher's knife?

Dancing Girls:

If your crazy supervisor's threat'ning you
Use a Heli-Coil and it's good as new
He will think the problem is in his head
And commit himself to psychotherapy!

Heli-Coil! Heli-Coil! When your backside is about to boil!

Man with Top Hat: "Available at fine auto parts stores nation-wide!"

But anyways, the operation went like this:
Yup, no threads worth trusting.

Aaahhh! Hahaha!!! Haaa!!! Mmmm....

The tap is just a hair oversized to make room for the insert.
Once complete, the system is actually quite a bit stronger
than the original threads.
Here they are: cute little buggers, aren't they?

In you go! The black thingy makes them go in straight.
Apparently that's important or something.

That's all the pictures I was able to get. The brake went on perfectly, and we barely had to adjust the caliper. The customer was pleased as a squirrel whose mortgage payments are very low, and rides the bike today thanks to Heli-Coil!