Mate has cracked his Specialized Enduro (~04 model) at the seatpost / toptube interface. It is not covered under warranty so he is now thinking of getting the crack welded.

I think this is a waste of money as it will be too weak at the new weld and will just crack again pretty quickly and possibly be dangerous to ride. Personally, I think the £30 for re welding could be put towards a new frame.

However I am no expert so wanted to see if there is any truth in my thinking or if he should just go for it?

Can’t hurt. I would’nt trust my wleds but someone who know what they are doing could probably do it. Why did it crack? Sounds like too little seatpost in possibly.

If you get an expert who is used to welding these sorts of tubes it should be Ok – will really need a sleeve or something put on and IMO a proper job will be far more than £30. Try Harris or one of other the custom sports motorcycle folk

Depends how it was welded in the first place. Some frames are welded then the whole frame heat treated to strengthen the material and weldind and to releive stress. If you re-weld after heat treating you can temper/aneal the area and reduce strength. Basically the alloy goes soft. If the frames are not heat treated post welding then it may be Ok that is if the welder has the correct type of welding wire to weld the frame material. If he gets it welded keep a very close eye on it!

He is a big guy and has a lot of seat post showing but it was comfortably over the minimum insert (if that makes sense?)

TJ – will pass on the tip – thanks

Why is it not covered under warranty? Is he not the original owner?

Depending on the size of the crack you could drill it to stop it spreading. If its welded it will need heat treated otherwise it will probably only weaken it. Ive heard after re-heatreating the bike will be around 85% original strength. Im not an expert though!

Mine’s held fine

[/quote]Why is it not covered under warranty? Is he not the original owner? [/quote]

He bought 2nd hand

As for the heat treating thingy – some alloys need it and some don’t – and the folk used to alloy fabrication will have the facilities to do it anyway I would have thought – but they won’t be cheap. Harris for example make their own alloy frames on site ( for motorbikes)

My ’03 enduro went in exactly the same place. The ’04 has thicker tubing in that area.
IIRC Spesh ally frames are heat treated

If it’s 6000 or 7000 aluminium alloy (historically, if US, likely to be 6000, if Far East 7000, but I digress) they will more than likely be heat treated after welding. This can be done for individual welds with heat blankets, but even then achieving the correct temperautre and soak times to match the material and the welding process is a bit hit and miss.

A while ago, the weld between the BB and the seat tube cracked on my commuter. I know a guy who welds thin section Alu for a living, but can’t do the heat treatment. As I knew the frame was bin fodder, so he ground out and welded up the crack anyway and I ran it again to see how it woudl last. 2 weeks later, the frame was in the bin.

Is 7005 not the one that doesn’t need heat treating?

2000, 6000 and 7000 can be precipitation hardened (heat treated), the rest can’t

Edit: 7000 series is generally stronger that 2000 and 6000 so MAY not need to be heat treated for a given application, but the strength reduction due to annealing in the heat affected zone is so great that you pretty much have to on a frame where the section thicknesses are so small and all of the welds are ‘critical’ (i.e. – very little redundancy)