Cracked ally frame ... weldable?

[wafers]

I dug out my ally framed Saracen Mantra 1 from the back of the garage earlier, cleaned it up and noticed the headset was loose. Unfortunately I didn't think logically (which is REALLY annoying as I've normally got a fair-share of common sense!) and tightened it too much. Basically it didn't sort the problem enough, so I tightened it some more. Next thing I know I have a 10mm long hairline fracture in the headset tube.
The bike is in excellent condition otherwise, and has hardly been used.
What are people's opinions on the damage - is it repairable/weldable? I'd be gutted to have to bin the frame!
Any thoughts appreciated.

 

[GSB]

Which alloy is is made of? Common ones are 6061 and 7005 (there are others, but they seem to be rarer).

Weld repair is fairly easy, assuming you have the skills and the right filler, but its a fair bet that that the headtube will need reboring, and if there is extensive heat treatment required a complete new paint job too.

Its possible, but the expense may well make it a labour of love rather than financial common sense.

 

[bren]

mantras are 7005 so its weldable, also helps that its not strictly a fatigue crack.
shouldnt take more than 10mins to weld once the paint is removed from the area. The problem then, is as GSB says, it will take some time consuming machining to get the tube round again and ready to accept a HS cup. will likely cost more than its worth. if i was to attempt a repair through the books at my place it would probably cost £50-60 plus the dreaded VAT.
I sold my pretty much mint Mantra last month for £50!

 

[danson67]

It can be repaired...if you think it's worth the effort/cost:

You can either get an external ring fitted

or have the crack re-welded. Here's one I might have had something to do with.

All the best,

 

[wafers]

mantras are 7005 so its weldable, also helps that its not strictly a fatigue crack.
shouldnt take more than 10mins to weld once the paint is removed from the area. The problem then, is as GSB says, it will take some time consuming machining to get the tube round again and ready to accept a HS cup. will likely cost more than its worth. if i was to attempt a repair through the books at my place it would probably cost £50-60 plus the dreaded VAT.
I sold my pretty much mint Mantra last month for £50!

Bugger! Looks like I'll be looking for a new frame then... :cry:
Don't suppose you have any more Mantra frames?!
* Goes off to wanted threads to post an ask for bike/ frame in Cornwall.

 

[wafers]

It can be repaired...if you think it's worth the effort/cost:

You can either get an external ring fitted

All the best,

How does this work? Like the sound of this...

 

[danson67]

Do you know anyone with a lathe? They're stainless steel rings turned down internally to be a slightly undersize tight fit on the head tube outside diameter.

• Remove the paint around the top of the headtube to get a metal-to-metal contact.
  Cool the headtube, heat the headring, assemble.
  As the headring cools it shrinks on tight.
  Closes the crack, reinforces the end of the headtube.

The headtube then probably needs a fresh reaming out to make sure the headset cup fits well.
Might even be able to do something by press fitting an external ring using a headset press...

All the best,

 

[wafers]

Do you know anyone with a lathe? They're stainless steel rings turned down internally to be a slightly undersize tight fit on the head tube outside diameter.

• Remove the paint around the top of the headtube to get a metal-to-metal contact.
  Cool the headtube, heat the headring, assemble.
  As the headring cools it shrinks on tight.
  Closes the crack, reinforces the end of the headtube.

The headtube then probably needs a fresh reaming out to make sure the headset cup fits well.

All the best,

That sounds fantastic. Going to ask around-just need to find a bike friendly fabricator in Cornwall now!
Cheers!

 

[danson67]

I often find the old British motorbike, car racing or model engineering community helpful for this sort of thing.
They also appreciate that, while the frame might not be worth much money, it's worth a lot to you.
Loads of retired old engineers who enjoy a little project and have the kit and experience to do it. Blokes in sheds!

The last job I had done was paid for in beer, tea and biscuits. :shock:

All the best,

 

[Chopper the ex Copper]

It can be welded, but 7005 is heat treated so the metal heated during the repair will lose its strength characteristics. I'd strip it and weigh it in for scrap myself.