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Old 07-19-2009, 03:39 PM   #1
clintnz OP
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KTM 640 Subframe Repair & Strengthening

I just had a crack repaired & some bracing added to the subframe on my 640 & thought I'd post up some pics.

The crack was in the rear end of the tube that the tool box mounts to. (see pic) The right side subframe rail was bent down a little, probably from a big endo I had a while back, & I think this has put stress on that tube & then it has cracked. I recently did lots of corrugated roads in outback Australia with a load on the rear rack & that was likely the final straw. Most of my gear is carried in my panniers that are mounted well forward, apart from one stretch of the Oz trip where I had 10L of gas on the back there is usually at most 7kg on the rear rack.

There was a thread over in the Oz forum about broken 640 subfames but I thought I should post this up here for the masses. There is also a pic of Loaded's similar repair efforts in this thread (scroll down) The std failure mode seems to be for the tool box tube to crack like mine, then the left side rail gives way just behind where the gusset on that side ends. So keep an eye on the end of that lil' bit of tube, especially if you carry a load on the back.





I cleaned it all up & made the gussets then got a friend who is a pro TIG man to weld it up. I just used 2mm steel. Cro Moly would have been the proper thing to use but I couldn't find any closer than the USA & several weeks delivery.

Cheers
Clint
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clintnz screwed with this post 07-20-2009 at 02:16 PM
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Old 07-19-2009, 05:24 PM   #2
Dotbond
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That is some serious bracing! I have already lost my toolbox and the tubing it was bolted to, broke right off. Have had some welding done to the left side of the subframe as well. May have to look strengthening both sides at some stage.

Thanks for the post Clint.

Trev.
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Old 07-19-2009, 08:38 PM   #3
clintnz OP
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Quote:
Originally Posted by Dotbond
That is some serious bracing! I have already lost my toolbox and the tubing it was bolted to, broke right off. Have had some welding done to the left side of the subframe as well. May have to look strengthening both sides at some stage.

Thanks for the post Clint.

Trev.
I'd look at adding some bracing sooner rather than later if I was you, without the toolbox holder/brace there's a good chance she'll just crack again. I firmly believe that it is a waste of time just welding up anything that has broken under normal use - a redesign or some extra metal is required to prevent the same problem happening again.

Cheers
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The wilderness, the desert - why are they not crowded
.................................................. .....with pilgrims?
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Old 07-21-2009, 09:56 PM   #4
meat popsicle
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Ya know, since I saw Loadedagain's subframe bracing years ago, and countless posts about bent/broken subframes I wonder if the few pounds saved by the "racing" subframe are really worth it... on a supertanker.

Thanks for the nice how-to post Clint, and thanks for bringing your link in too crazybrit.
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Old 01-27-2010, 02:48 AM   #5
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Do you guys know if the subframe on the LC4 is made of the same steel as the main frame - 25CrMo4?

Cheers
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Old 10-06-2010, 10:48 PM   #6
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Nice work Clint


Good to know there is an expert nearby when I get my Adv
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Old 10-18-2010, 03:20 AM   #7
overlandr
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Quote:
Originally Posted by LukasM
Do you guys know if the subframe on the LC4 is made of the same steel as the main frame - 25CrMo4?

Cheers
We really need a KTM factory mole. I bet the German fora have them.
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Old 10-18-2010, 03:31 AM   #8
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Quote:
Originally Posted by overlandr
We really need a KTM factory mole. I bet the German fora have them.
I actually called HQ here in Austria and managed to get through to a factory engineer a while ago. Subframe is indeed made of the same CrMo steel.

Depending on how serious you take your welding you could use a different rod and maybe pre/post heat treat the welds. Different opinion depending on who you ask, although race car guys and roll cage fabricators are probably a good source. Carroll Smith recommended to pre-heat the metal and to normalize the welds afterward in "Engineer to Win" (I think....).
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Old 10-18-2010, 04:54 AM   #9
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Quote:
Originally Posted by LukasM
I actually called HQ here in Austria and managed to get through to a factory engineer a while ago. Subframe is indeed made of the same CrMo steel.

Depending on how serious you take your welding you could use a different rod and maybe pre/post heat treat the welds. Different opinion depending on who you ask, although race car guys and roll cage fabricators are probably a good source. Carroll Smith recommended to pre-heat the metal and to normalize the welds afterward in "Engineer to Win" (I think....).
Thanks. Metals seem much happier with Annealling - look at some welded structure fractures and it often occurs at the edge of the weld. I gather the welding of (eg) titanium can involve a large degree of pre and post (welding) heating where access to ovens is reqd. I guess Akra would be familiar with this material.
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Old 04-04-2011, 01:23 PM   #10
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Thumb Sweet

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Old 04-04-2011, 02:57 PM   #11
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the subframe is fine and all, but i hardly see it with the 70 series in the background
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Old 04-04-2011, 04:49 PM   #12
clintnz OP
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Originally Posted by 2 SPOT View Post
the subframe is fine and all, but i hardly see it with the 70 series in the background
If a glimpse of a half disassembled 70 turns you on that much, you'll certainly enjoy the full story http://www.offroadexpress.co.nz/Foru...hp?f=18&t=2123

Cheers
Clint
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The wilderness, the desert - why are they not crowded
.................................................. .....with pilgrims?
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Old 04-04-2011, 09:07 PM   #13
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For Cromo you could braze it.
Cool it slow>?
Am I wrong?

Well anyway I have.
bill
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Old 04-05-2011, 01:50 PM   #14
clintnz OP
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Quote:
Originally Posted by bmwktmbill View Post
For Cromo you could braze it.
Cool it slow>?
Am I wrong?

Well anyway I have.
bill
Yep, nowhere near as strong as a weld but it will work in pinch. If an oxy acetylene plant is available Cro-mo can apparently be welded quite well by a skilled hand on a torch too. From my dim memory of engineering class Cro-mo does need to be post heat treated for totally optimum weld strength, but one reason for its popularity is that just letting the weld cool slowly gets you near as dammit.

Cheers
Clint
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The wilderness, the desert - why are they not crowded
.................................................. .....with pilgrims?
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Old 04-05-2011, 04:23 PM   #15
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This is a project that has been on my mind for a while now, just another reason to buy a welder!
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