Australian Cycling Forums - Bicycles Network Australia

I couldnt help myself. At the recycling centre today they had a Trek 4700 from 2002ish which had been in a house fire and the rear wheel had caught fire. The tyre burnt, as they do, and the rim is quite badly buckled. It may have taken a hit too. But the Deore groupset and shocks are still all good.
Anyways, the rear triangle is black with soot but as far as I can tell without yet pulling it apart, all it needs a new back rim and spokes (hub looks clean) some new rear brakes and some cables. But how can I tell if the frame is safe after taking the heat from a burning tyre? Most of the paint looks OK under the soot but not all of it.
My burning desire to resurrect this bike will give me a warm feeling yada, yada... Any help is good help.

I'm no metallurgist, but I'd be thinking that the heat treatment of the rear triangle may have been affected.

Shaun

I suppose I'm looking for a way to tell. Like warped metal or misalignment of the triangles or the temperature at which rubber burns or paint melts.

Take it for a ride and see...

Imagine how hot the tube gets when it's being tig welded. It's got to be at least worth having a go.

The only real way of telling would be to do a hardness test (comparing results from an obviously unaffected area with a potentially heat affected one), that gives you a results of Rockewell or Vickers hardness.

On a small peice of metal, this could be done easily, but a bike fram,e may be a bit harder.

The test can be somewhat destructive.

Give the bike a thourough clean and have a good look for obvious damage to paint and structure. Take some measurements and check the frame alignment.

If it looks OK, swap in a wheel (if possible) and take for a gentle ride.

Or, you can always take it to a frame builder for a professional assessment.

Ride it and see .... Since it's the rear triangle, failure of the frame shouldn't kill you.

The other method is to give it to TooLongLegs for a day. If it survives, it's a good frame.

Cheers,
Graeme

OK. I'm just going to wipe off the soot and chuck another wheel in and try it. I'm sure if there's damage I'll at the very least hear some creaking metal and I'll just work my way up to a few jumps.
Cheers.

justalf wrote:OK. I'm just going to wipe off the soot and chuck another wheel in and try it. I'm sure if there's damage I'll at the very least hear some creaking metal and I'll just work my way up to a few jumps.

Inspect the welds and tubing with a light after each ride for a while. If any cracks appear then you'll know it's not safe. If there is damage in the rear triangle it's not as dangerous as it would be at the front end, but still be wary.

justalf wrote:Most of the paint looks OK under the soot but not all of it.

I would say that if the paint is ok it wouldn't have been hot enough to damage the aluminium.

A.

Frames are usually heat treaterd after welding.

My experience is with aircraft ali. 6061T6 and the like. You need to get it fairly hot to soften it much. Probably hot enough to char a bit of pine held against it. We used to use soap and heat until it charred.

If the paint more or less survived it's probably OK. Probably would be concerned a bit if it was an aeroplane but a bike is not so critical

Much of the Ali's temper and strength will return over a few days anyway strangely enough.

Give it a try and see how it goes.

John Lewis

+1 to taking it out for a ride but make sure you take a friend with a video camera with you so if it does all turn to pot you can send it in to Funniest Home Videos and recoup some of your medical expenses...

Sorry, not much help I know...it's Friday evening and I'm still stuck in the office...

So my plan now is to put in a new wheel, find a large cycling friend with a video camera and tape his efforts trying to break the frame.
You have all been so helpful.

The frame seems to be fine. Took it for a quick ride and all went well. Seems that a bit of extra heat treatment to a frame makes little difference.

Just thinking (ouch! ) What sort of temperatures are used when you get a powder coat paint job? May be worth reading about aluminium frame repairs here