I cracked my #&$^*% frame!!!

[Clayton Stothers]

Ok, its a 2005 Birel. After a day of practicing i noticed that the main seat support had a crack that went almost halfway around the post. It looks like the metal failed rather than the weld because the crack was slightly above the weld. Anyway, what would be the correct way to fix this? I can easily shoot it with a MIG welder but it won't look like the original TIG weld (nor be as strong). So do i have to take it to a shop to get it TIG'd or is the MIG sufficient? Anyone have this happen before?

PS. Before you ask, no i didnt hit anything... i mighta hit some curbing a little hard but nothing abnormal.

Thanks,
Clayton

[George Petry]

I’ve seen this happen before, usually from having to spread the seat struts apart in order to get a seat to fit. My First kart broke in the same spot. If you’re a good mig welder, and have the proper wire, I’m sure that would be a good fix. I’m in the metal trades, and am fussy about such things and always tig weld anything on a kart…that being said, I believe most kart frames are mig welded today.

[Dan Davis]

Yup, if they use 4130 steel (which I am skeptical of in many modern chassis) and used a MiG, the chances are that the metal around the weld suffered from hydrigen embrittlement from cooling too quickly or not being preheated. Broken seat struts are common. No biggie, clean the powder coating off around the break and have someone weld it up. TiG is preferable but MiG will work for ya.

[Erik Frank]

This is a common failure on many kart frames. The crack occurred in the heat affected zone of the weld. The seat struts and steering upgrights are one of the first places that cracks appear, then the rear bearing cassettes, and then the front kingpin brackets.

Since you've found one, it is smart to inspect everywhere else carefully. Unfortunately powdercoating tends to mask the problems.

I've killed a frame with fatigue, and its not fun to have a failure on the racetrack (roadracing) like that.


-erik
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Member of the Fisher-Price Racing Team

[Clayton Stothers]

Alright thanks guys, is there any way to tell what kind of steel is used? If its 4130 then i'll TIG but if its just a mild steel then i think i could get away with a good MIG weld. Anyone know what steel Birel uses on their frames, specifically the seat strut?

[Kevin Willmorth]

Birel, as well as most all other kart builders, and MX bike makers for that matter, use MiG to weld the chassis in the first place, so repairing it with MiG is certainly not an issue. You can always use mild steel wire to weld alloy steel, especially for something like a seat support. Weld it up as quickly as possible to keep heat to a minimum. I've wrapped aluminum foil hot welds to slow the cooling cycle, although I have no proof it means anything.

[Joshua (BlueBayou) Lyon]

This happens often with the Birel. Once it is welded, make sure that the tab is parallel with the seat and that the bolt isn't overtightened.
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Catch U Later - Joshua

[Dan Davis]

It is hard to tell what they used. It is possible that kart manufacturers use 4130 for the main frame rails then use mild steel for the seat struts knowing that they will be bent to fit various seats. I have welded 4130 many times with a MiG with no adverse effects that I know of. I think you will be OK either way you go.

[Paul Hunter]

I take some threaded rod appropriate to the size of the inner tube diameter and cut off a piece about 3 inches long. hammer it into the hole then hammer the broken piece onto it then weld the joint. I use mild steel stick only because that is all I have available but all other forms of welding are good. I garantee it wont break there again as welding only would.

Hope this helps out.

Paul