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My cycling buddy, er, rode in front of a car last July, sending him over the bonnet and his Tarmac 15 ft into the air to land on the hedge. The RH chainstay was crushed and his house insurance bought him a new bike. I'm thinking I might buy the frame off him and have a go at a repair, my reckoning being that if the chainstay is about 30% undamaged it will have residual strength and any reinforcement will be good. Now my problem is that the chainstay is a tapering oval shape, which will be difficult to reproduce cleanly if I cut out the crushed section so I'm thinking I might just rub down to the carbon weave then wrap the entire length of the stay in a couple of layers of carbon going at 90 degrees then at 45 degrees. The worst that can happen is that compressive forces can break the chainstay as I climb the first hill so I think this could work.
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Any comments? Any recommendations for a DIY repair kit?
Get it fixed properly or bin it.
That crack along the top looks very long, your methodology seems reasonable, but I wonder if it's too far gone for that.
The crack is very long but it separates the crushed outside of the tube from the intact inside. How would a "professional" fix this "properly"?
RH chainstay takes lots of cyclic loading. Lots of compression.
Tough one that.
That's my thinking: if the repair is good enough to resist the compressive effect of the chain, I reckon it will be good enough for me to ride. I guess the first test of the rebuilt bike would be to take it up my local 33% climb.
The crushing injury to the tube was very broad and well distributed; probably where the plastic front bumper of the car hit it. Consequently the inside half of the tube is completely intact and rigid as far as I can tell. The same impact pushed my buddy's right calf against the bike hard enough for the derailleur to penetrate his skin, which was the only injury apart from bruising.
Possible to open it enough to fill with expanding foam, rub down as you describe and then repair ?
Idea being the foam will give some strength from a solid core.
Or, use a spoon.
I'd be reluctant to do that because there's a cable running through it.
The crack is very long but it separates the crushed outside of the tube from the intact inside. How would a "professional" fix this "properly"?
Wasn't meant to be a slight on your potential skill (if it came across that way), but a professional will have access to autoclaves and experience and what not, rather than just some pre-preg and epoxy. I'd have a punt on a seat stay, but a chainstay, particularly RH one... not so sure.
Well the good point is that the chainstay is intact at both ends, meaning that the stress will be transferred evenly through the BB area and the dropout. Along the middle section of the stay the stress is evenly distributed with no stress risers at all in the frame shape so in the same way that a cardboard tube is a very rigid structure when stressed in a bending way, I'm thinking that a sleeved chainstay will also be strong enough.
Can't see the picture due to the works internet... But...
If the chainstay isn't the same length as it should be, you'll have great difficulty in repairing it so everything is perfectly aligned, or perpendicular.
No the inside half of the chainstay is intact so the frame geometry is not compromised. Thanks to the broad impact the chainstay is "bruised" on the outside meaning the tube has lost its rigidity and can be crushed slightly when you squeeze it between thumb and fingers.
personally if I were to have a go, I'd be comfy with extending a wrap about half as long as the top crack again, both sides of it (so probably up to the BB. As many layers as you like. I'd go for 5 at least, 90/45/90/45/90 layup. follow application instructions from the likes of carbonmods and keep an eye on it when you're done.
Any separation at the joints then bin it.