If you have a torque wrench, use the damn torque wrench!
I’m going to print that out and tape it to the handle of every one of my hex wrenches bigger than 5mm. I was installing a rear brake on my P3 this afternoon and got a little carried away with the bolt that fixes the brake mounting plate (or whatever that thing is called) into the frame. Sure enough, the bolt started slipping and when I backed it out, I saw fragments of what looked like a helical insert coming out with it. Now the bolt is quite loose even when screwed in all the way and it no longer holds the plate, and therefore the brake, tightly against the frame.
I had a few minutes of panic where I thought I had just totaled my frame less than four weeks out from my last big race of the season, but now I’m grasping a little ray of hope that I might just have to rethread the hole somehow. I’m not sure how to do this, though, and I can’t take it to a professional because I don’t know anyone in South Korea who I would trust to know anything about rethreading a hole in a carbon time trial frame, and I don’t have enough time to send it to Calfee. If the frame is well and truly broken beyond repair, I’ll have to ride a road bike for my upcoming 70.3, but I would really rather get this fixed! Can anyone help me out?
Easiest way is to drill and tap the hole for the next size up and get a new bolt to match. Not something I’d want to do for the 1st time on a p3 though.
If you know of or can find someone who has their A&P (Airframe and Powerplant) license (or equivalent). These are the folks who do maintenance and repairs on airplanes.
Helicoils are used all over the place on airplanes, someone with that background is likely able to help evaluate your problem and then come up with a repair.
It may be as simle as replacing a helicoil. Contrary to your observation, helicoils don’t typically bust up into fragments, it may be the carbon threads of the frame. There are two ways to repair a stripped helicoil. Replace it with the next size up in which case you need the correct drill size and the special helicoil tap (and helicoil installation tool), in that case you’ll also need to adapt your brake plate to accept the larger bolt. The other choice is an Over-sized helicoil repair; Twinsert is the name of one version. You still need to drill out the frame and tap with the special twinsert tap (or what ever brand) and install the new twinsert but you’ll be able to use the existing bolt and no modiofication to the brake.
I’m not familiar with the P3 but I know that a regular helicoil thread insert is designed to go into a metal component, Not Carbon. I’ll *assume the stripped *female threads are part of a metal nut-part imbedded into the frame to accept the bolt.
If the only damage is the female threads of the nut, then a regular helicoil repair kit will work. Just follow the instruction about drilling the old threads out, tapping & inserting the replacement threads.
If the entire nut-part is damaged then you have to replace the nut, probably with some epoxy bonding.
Some pix would help
I have repaired a P3 in the past with the same problem by reaming out the remaining threads, then installing a Rivnut using JB Weld epoxy to hold it place, the Rivnut was expanded lightly to compress against the sides of the hope. Requires filing/smoothing off the surface with a Drexel tool so that brake attachment plate sits flush at the end of the repair. Take your time, patience, and allowing adequate drying time of the epoxy. If you don’t feel comfortable anyone who has worked with fiberglass boat or kayak repair will have no problem doing this. The repair I did has lasted 3 years so far.
Hank
I got a PM from Damon Rinard (senior engineer at Cervelo) who confirmed that I stripped out the threading in the rear brake mount. The good news is that he said there is an aluminum insert in that section of the bike and all I would need to do is use a standard Helicoil kit to repair the mount. I ordered an M6 x1 Helicoil kit and I’ll try my hand at it when it arrives in a week or so.
The idea of taking a drill and tap to my P3 is a bit unsettling, but I guess that’s what I get when I am too lazy to walk across the room and pick up my torque wrench… d’oh.
The idea of taking a drill and tap to my P3 is a bit unsettling, but I guess that’s what I get when I am too lazy to walk across the room and pick up my torque wrench… d’oh.
Serious question - what makes you think having the torque wrench would have saved you?
I don’t know of a published torque specification for that bolt, but the torque wrench would have let me know that I was using way too much force. I have the smaller Park Tools beam one and I would have probably deflected it completely off the scale.
I don’t know of a published torque specification for that bolt, but the torque wrench would have let me know that I was using way too much force. I have the smaller Park Tools beam one and I would have probably deflected it completely off the scale.
The reason you stripped the threads is because the aluminium threads were too soft for the torque you applied. When you install the helicoil that problem will be mitigated
Be sure to use some kind of lubricant when drilling and especially when tapping. You’ll get away with drilling it dry but if you tap aluminum dry it WILL gall the tap and strip the new threads out. If metal working oil can’t be found, motor oil can work or even (gasp!) WD-40 can be used too. If you can make a block with two holes in it, one the same size as the drill and the other the same size as the OD of the tap you can hold it flat up against the surface that the hole goes through to help you drill and tap the hole straight. Google search “machinist tapping block” or something along those lines and you’ll get the gist. Take your time. Thread the tap in slowly then back it out after a turn or two and clear the chips then re-lubricate and go a little further until you get it deep enough for the insert to be installed. I’m a machinist and deal with drilling, tapping, Helicoils and other stuff like that regularly. If you have any questions just pm me and I’ll be happy to answer any other questions. Good luck!
Thanks for the detailed advice on tapping - I used some 10W40 motor oil for both drilling and tapping and it worked out very well. I was a little apprehensive about taking a power drill to my P3, but the operation was done surprisingly fast. A few notes for any unfortunate soul who might have to follow in my footsteps:
the Helicoil kit sold on Amazon does not include T-handle turners. The tap has a standard 1/4" square driving end, so I used an adjustable T-handle ratchet which worked well enough. The Helicoil installation tool (the long black threaded thing that looks like a bolt) has a much smaller square driving end, and my adjustable ratchet barely held it, but you don’t have to use much torque to install the Helicoil itself so it worked just fine.
You’ll have to use a corded power drill. I first tried a battery-operated drill, after making sure it had a full charge, and the battery ran down before I’d drilled more than 1/8". Sharp drill bits help, and liberal application of metal working fluid or oil is - like speedboarder9 said - a must.
You only need one M6x1 Helicoil insert. A M6x1.5 might work also, but the regular length held the bolt just fine.
I’ve done a helicoil before. I had a tap and die set so I had the handle and a pretty fair selection of GOOD drill bits. I do use a high end cordless drill with zero issues.
I stripped a caliper mount bolt on a Fox fork. I purchased a helicoil kit from Amazon pretty cheap. Found a how to video on youtube and went at it. Very simple and easy to do. Took all of five minutes.
Just a note for clarity - M6x1 refers to the thread size, not length: Metric, 6mm diameter, 1mm per thread. M6x1.5 would be a different (coarser) thread, incompatible with the bolt. Length is specified as part of the description, and you’re right, standard length is fine but longer would also have worked well.
Oh no… the exact same thing happened to me yesterday. The irony is I used a torque wrench but had it set to “brake caliper” spec which is 8 - 10 Nm so I stripped the thread…
Serious question. Since the threads are just epoxied (they are, right?) into CF frame material, can’t it be epoxied back without tapping for a one-bigger size up? Unless there’s damage to CF?
I always use a torque wrench. 4-5Nm for bolts into CF. 8-9 Nm metal to metal. Typically.
Serious question. Since the threads are just epoxied (they are, right?) into CF frame material, can’t it be epoxied back without tapping for a one-bigger size up? Unless there’s damage to CF?
I always use a torque wrench. 4-5Nm for bolts into CF. 8-9 Nm metal to metal. Typically.
I frankly have no experience in both but by just looking at the threads in the frame it looks like it will be pretty hard to remove them without damaging the surrounding paint job (and then install a new one). From all the search online it looks like tapping is a relatively easy procedure although taking a drill to the bike sounds very painful right now
