OTK Weld quality - Kart Frame Metallurgy

Anyone else seeing poor welds on their kart frame?
Had both left side seat posts break this weekend on my sons kart. Got paint cleaned up tonight and both welds failed in the HAZ indicating poor temperature control or PWHT on the chrome moly tubing. For a frame that costs 2500 the Italians should do better…
This frame was purchased in March/April after totaling the previous frame in a wreck, so it isn’t old and tired.
Going to Tig it out tomorrow and wrap the welds. If I am not happy with the cooldown I will heat it with a small torch and wrap it to stress relieve the weld.

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I’ve always been confused why they couldn’t just put some thicker base at those pressure points, considering those always crack on you.

Yeah seen quite a few OTKs from the last few years with those exact cracks.

Is this just an OTK thing? This is where I would crack my compkart, too.

This set of cracks isn’t a load issue, it is a weld quality issue. The location of the cracks indicates localized weld stresses that were not relieved. This is something that just shouldn’t ever be allowed to happen on chrome moly welds. Too much heat input when welded (look at the very large weld beads) combined with rapid cooldown and no PWHT. If that weld had been PWHT it wouldn’t crack right in the HAZ. The location of both support cracks tells the story…right at the toe of the weld in the HAZ where the weld and base metal meet. It is a weld process or weld control failure, not too much stress or too small of a support. If done correctly, those tubes should fatigue and tear in the base metal away from the weld when overloaded.

I’ve got a 2021 OTK chassis that 've had welded 2x now due to failures on the seat struts. Fortunately, we run the Orange Exprit, so the cracks are easy to see.

When I look for OTK karts on FB Marketplace, almost all of them have a welded seat strut, regardless of age.

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Its not only a OTK thing, a lot of karts are getting cracks all over the place not only at the seat struts

This is just a standard kart thing across the board. OTK, Comp, BirelART, MGM, Eagle, Haase, CRG… I fix em all at the track all the time. OTK isn’t special in this regard.


@CrocIndy Maybe they are all skimping on temperature control and PWHT practices. You can’t cut corners on chrome moly welding, especially in a high load or hydrogen service. This weld point isn’t H2, but it certainly can be pretty high load.

For a $2500 chrome moly chassis, I find this particular failure mode to be pretty darn frustrating. Straight up poor process control.

OTK is not standard 4130 FYI. It’s a non-commercially available proprietary composition. Go-kart chassis are not made to be durable and long-lasting. They are made to be fast for however long they last.

We have actually went out of our way on our in-house chassis to make sure the seat strut issue is not something that happens.


I know this is a commonly held belief, but considering you’re making your own chassis….How do we know this?

Well for one, everyone’s chassis would feel the same if it was all 4130. And they sure don’t.

OTK puts a lot of effort into being secretive about the material. Supposedly they have exclusive rights in the sourcing to their material as Matt said.

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I hacked off a piece of tube and had a full analysis done. :joy:

Playing devils advocate here, but there’s a ton of things that make chassis “feel” different in addition to the tube composition.

Seat, spindle rake and other steering geometry, frame shape, and of course tires. A logical tester would do their best to isolate all of these of course, but as drivers we’re not always the most logical bunch at times.

Of course. I have no data and haven’t isolated all the variables but in my experience driving many different karts now, I can tell you the OTK flexes differently than some other karts. And it certainly feels like the material is different. How it reacts to input is different and in my mind that feeling I’m having isn’t from different geometries or frame designs, it really does feel like the tubing works differently. Could be confirmation bias.

Or you could do like Matt noted and get a piece of tubing analyzed.

I know others have done that as well.


For some reason whenever I weld an OTK it always gives me a hard time, the metal does weird things in my experience. I haven’t had any issues with other brands I’ve welded. Always acts very contaminated even if cleaned up well. I’ve welded a lot of karts too unfortunately.


I don’t have a clue what grade Cr-Mo material they use, only that they claim to use it. Curious as to what is actually is?? Docol? That is stuff I know nothing about.
I assumed 4130 based upon the CrMo claim on the OTK site and the nature of the weld failure I am looking at. Looks an awful lot like a work hardening failure in the HAZ of a high stress cyclical loaded connection to me???

As for the durability, March to September with no major wrecks on this chassis (can’t say for the last one). No way it should break running LO206 for 6 months!

It’s a CrMo, it’s just different composition. Are you hanging a bunch of lead on the seats? European chassis are designed for small guys and low weight classes.

Most of the failures seen are due to putting way too much weight stress on these small struts. That’s why they crack at the tab. That’s why they crack at the weld. That’s why the lower tabs crack off.

When we re-weld it, no matter how good of a job is done, it’s going to break again then again then again.

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Your tall driver surely doesn’t help with all that pendulum weight leaning on the seat tabs. We’ve battled the same issue on taller drivers. They tend to break the tabs more. I think I’ve only cracked tabs or struts 2 or 3 times every on OTK stuff.

@CrocIndy 6-4" 165lb or so driver. 15 lbs of lead on seat, 5 low on back, 5 low on left, and 5 under front left corner. So we don’t run a ton of lead on the seat, but we have a really tall kid in it. Also because of the height, we run with no extra struts in 206 to free up the rear.

@tjkoyen Especially when running no extra struts helps his kart so much. :woozy_face:
On another note, he managed a P3 qualy when the seat busted on lap 3 and a P2 finish on the night with a bolt on seat post keeping it together. :man_shrugging:

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