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PostPosted: Wed Jan 17, 2018 11:45 pm 
Retro Guru

Joined: Thu Jun 19, 2014 2:41 pm
Posts: 1212
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


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PostPosted: Thu Jan 18, 2018 8:34 am 
retrobike rider
retrobike rider

Joined: Thu Jul 04, 2013 10:32 pm
Posts: 937
Location: Preston
Danson is your man for that ste


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 Post subject: Re:
PostPosted: Thu Jan 18, 2018 9:00 am 
Gold Trader
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Joined: Thu Mar 29, 2007 1:08 am
Posts: 3191
Location: Kray Territory
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 :)


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 Post subject: Re:
PostPosted: Thu Jan 18, 2018 9:28 am 
Retro Guru

Joined: Thu Jun 19, 2014 2:41 pm
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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


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PostPosted: Thu Jan 18, 2018 3:12 pm 
retrobike rider
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Joined: Tue Jan 29, 2008 11:04 pm
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Location: A wretched hive of scum and villainy...
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:
Attachment:
Crack.jpg
Crack.jpg [ 136.94 KiB | Viewed 776 times ]

Attachment:
Repair1.jpg
Repair1.jpg [ 125.74 KiB | Viewed 776 times ]

Attachment:
Repair2.jpg
Repair2.jpg [ 169.41 KiB | Viewed 776 times ]


All the best,


Last edited by danson67 on Thu Jan 18, 2018 4:13 pm, edited 2 times in total.

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PostPosted: Thu Jan 18, 2018 3:25 pm 
Old School Grand Master
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Joined: Tue Jul 05, 2005 3:14 pm
Posts: 14574
Location: Warwick
Sterling work. Just brilliant.

Is it viable replacing a top tube? Is it even possible to reweld one in?


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 Post subject: Re:
PostPosted: Thu Jan 18, 2018 3:31 pm 
Retro Guru

Joined: Thu Jun 19, 2014 2:41 pm
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Mines at the front top about the same size as yours


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PostPosted: Thu Jan 18, 2018 3:43 pm 
retrobike rider
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Joined: Tue Jan 29, 2008 11:04 pm
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Location: A wretched hive of scum and villainy...
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...

Quote:
Is it viable replacing a top tube? Is it even possible to re-weld one in?

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,


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PostPosted: Thu Jan 18, 2018 10:20 pm 
Gold Trader
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Joined: Sat Aug 02, 2008 3:12 pm
Posts: 9163
Location: Oh Canada!
danson67 wrote:
Here's a Manitou which I did recently:


whoa, beautiful job! :shock:


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 Post subject: Re:
PostPosted: Sat Jan 20, 2018 1:12 am 
Retro Guru
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Joined: Wed Jun 15, 2016 8:39 pm
Posts: 770
Location: Southampton, Hampshire
That's some beautiful engineering right there. A repair like that is a work of art.


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