themountie
Senior Retro Guru
- Feedback
- View
Hi guys I have a 95 Marin nail trail with a 1.5cm hair line crack starting at the top
Is it worth it welding it
Is it worth it welding it
To repair or not repair cracked head tube
- Thread starter themountie
- Start date
Re:
Damn, sorry to read this... A reweld is possible but care is always needed as the alloy will weaken with the reheating. The HT takes a lot of stress as well. Danson on here would however do an incredible job, if previous work in here is anything to go by (most likely either reinforcing or replacing the tube at a guess).
The above (correct way) won't really be a cheap fix, so unless you are especially attached to the Marin I would retire this to the wall to be honest. There are plenty of similar frames available for not much outlay.
Hope that this helps a bit
Damn, sorry to read this... A reweld is possible but care is always needed as the alloy will weaken with the reheating. The HT takes a lot of stress as well. Danson on here would however do an incredible job, if previous work in here is anything to go by (most likely either reinforcing or replacing the tube at a guess).
The above (correct way) won't really be a cheap fix, so unless you are especially attached to the Marin I would retire this to the wall to be honest. There are plenty of similar frames available for not much outlay.
Hope that this helps a bit
themountie
Senior Retro Guru
- Feedback
- View
Re:
My farther owns a engineering company so I could get it welded for free but just deciding weather its worth it or weather it would survive and not warp
My farther owns a engineering company so I could get it welded for free but just deciding weather its worth it or weather it would survive and not warp
Warping shouldn't be a problem because it's such a chunky tube, but it will need to be reamed out post-weld for the headset fit, otherwise the stress of the headset press-fit will be concentrated back on the weld area.
Is the crack at the front of the headtube, away from the DT weld?
Anything round the back near the weld, longer than a few centimeters or opened up will probably need a new head tube.
My normal procedure for a small crack is to remove the clear lacquer from the tube and take the polished finish down, as this often has loads of contaminants in it. Degrease the whole area, chamfer out the crack to allow full weld penetration from both sides, re-clean.
Starting at the outside edge, weld down the crack on the inside of the tube. Re-melt the start position and repeat down the outside of the tube. I use 100A peak/65A base AC pulsed at 150/sec, +65% balance.
File or grind weldment in and out back to original surface and polish a bit.
Ream out the head cup seat, face the tube and chamfer the inside edge of the tube face to reduce future stresses.
I use 5183 filler to get a good post-weld strength without heat treatment. The normal 5356 used on 7005 alloys needs time to age or a heat treat. It will work OK unheated, but is more prone to fatigue cracking.
Also use Tempguard gel to prevent the re-heat from getting near the old welds which could be over aged by it, and also makes for a quicker heat/weld/cool cycle, which is also better for the final strength.
Here's a Manitou which I did recently:
All the best,
Is the crack at the front of the headtube, away from the DT weld?
Anything round the back near the weld, longer than a few centimeters or opened up will probably need a new head tube.
My normal procedure for a small crack is to remove the clear lacquer from the tube and take the polished finish down, as this often has loads of contaminants in it. Degrease the whole area, chamfer out the crack to allow full weld penetration from both sides, re-clean.
Starting at the outside edge, weld down the crack on the inside of the tube. Re-melt the start position and repeat down the outside of the tube. I use 100A peak/65A base AC pulsed at 150/sec, +65% balance.
File or grind weldment in and out back to original surface and polish a bit.
Ream out the head cup seat, face the tube and chamfer the inside edge of the tube face to reduce future stresses.
I use 5183 filler to get a good post-weld strength without heat treatment. The normal 5356 used on 7005 alloys needs time to age or a heat treat. It will work OK unheated, but is more prone to fatigue cracking.
Also use Tempguard gel to prevent the re-heat from getting near the old welds which could be over aged by it, and also makes for a quicker heat/weld/cool cycle, which is also better for the final strength.
Here's a Manitou which I did recently:
All the best,
Attachments
jez-4-bikes-max
Kona Fan
- Feedback
- View
Sterling work. Just brilliant.
Is it viable replacing a top tube? Is it even possible to reweld one in?
Is it viable replacing a top tube? Is it even possible to reweld one in?
themountie
Senior Retro Guru
- Feedback
- View
Re:
Mines at the front top about the same size as yours
Mines at the front top about the same size as yours
That Manitou one was front bottom side so more stressed at the front edge in normal use.
Very weird/rare to get just a top side crack...probably a badly fitted or over-tolerance headset cup.
I see quite a few shiny NOS frames with fancy Chris King cups to go with their cracks...
I have a PACE RC200 in at the moment for a head tube and seat-tube replacement.
Here's one I did with just seat tube a few years ago:
http://www.retrobike.co.uk/forum/viewto ... ing+a+pace
All the best,
Very weird/rare to get just a top side crack...probably a badly fitted or over-tolerance headset cup.
I see quite a few shiny NOS frames with fancy Chris King cups to go with their cracks...
Yes, fairly easy with a top tube, since there's no specific requirement on wall thickness, butts etc, unlike head-tubes and seat-tubes, so easier to source suitable tubes.
I have a PACE RC200 in at the moment for a head tube and seat-tube replacement.
Here's one I did with just seat tube a few years ago:
http://www.retrobike.co.uk/forum/viewto ... ing+a+pace
All the best,
