What are some considerations I should have when getting it repaired?
I assume this is chromium-molybdenum steel. Anyone know the specific alloy? 4130?
Should I look for someone who has a an OTK-specific jig or OTK-specific experience?
I assume the practice is to get it frame-tabled after and adjusted if needed? Or just weld it and send it?
Will this happen often enough that I should just tool up myself? I’ve TIG welded sections of championship-winning FSAE frames and suspensions before, but currently only have a small MIG.
I am speculating this is when it happened. First curb strike.
The engine mount has a scrape and handling felt off a few laps after this curb strike. I boxed at that point. Maybe snapped at impact or cracked then and broke a few laps later.
Given using curbs is non-optional at places, what are some mitigations people have used?
The kart currently has two silver seat seat brackets on the left and one on the right.
Am I just too fat?
I am 183cm (6’0”) and 86kg (190lbs). Roughly 12-15% body fat, 22-23 FFMI. I can probably get down to 82kg (180lbs) fighting weight, but not sure if much more for any extended period of time.
Thanks all. This kart ownership journey has been fun and frustrating at the same time. And thus, I guess, fulfilling. I appreciate all the help and advice this forum has given me. I also appreciate even more now the work the team mechanics and managers put in for the arrive-and-drivers.
Super common. Not a huge concern. There are two types of people in this world; those who have broken an OTK seat strut weld, and those who haven’t put their kart on the track yet.
I have always MIG’d and sent it. I gather that your style is to be very thorough and detail-oriented, but for me, stressing too much about this kind of thing isn’t worth it, so I just fire up the welder and fix it without too much thought. Sometimes it lasts a season, sometimes it breaks again right away. That’s why I just MIG it quick and go, because it’s probably going to break again regardless of how you repair it. Either way, it shouldn’t affect handling too badly, since you still have the main tube attached and you have an additional chrome strut too. Once it’s repaired, it’ll be basically good as new. Really no need to re-table or jig the chassis. Nothing should shift from that breakage.
You’re not too fat, don’t worry. I’m 140 lbs and I used to break them a lot too. I don’t think the curb strike necessarily did it, but you never know. That looked pretty tame. I’ve launched from larger curbs…
If not, what do teams do? Just buy a bunch of complete rollers and pull all the parts off as spares?
I went OTK because in >80% of the arrive-and-drive kart track days I’ve done around the world, the team have put me in either a Tony Kart or Kosmic. I’m familiar with and enjoy the handling characteristics of this chassis, so do want to stay with it, regardless of the “nuances”, which I’m sure every chassis has.
You can’t get bare tubes from OTK, but some teams will sell their used frames. After national race weekends you’ll often see a bunch of used kart ads go up from the bigger teams.
Most likely not, though Kartshop sell bare frames without problems as far as I know. Although, like TJ said big teams sell their chassis or frames after a race so you can look there, but be careful because those most of those chassis are heavily abused(in a good way) the weekend they used them so be careful.
@RyanCarag
We ran OTK our first 3 years in karting.
2017 Tony, no cracks over 15 weekends.
2022 LN kart with 2 frames over 45 or so weekends. Let’s see… 2 seat tabs, 1 entire left side both posts, 1 left side smaller forward post only, 1 right side full break and partial crack of tubes. We never had a re-weld on any repairs, all of those were crack in factory welds. All of the cracks were in the heat affected zone adjacent to the weld. It is an artifact of mass produced chassis where too much heat is being applied on Cr-Mo tube material. It just so happens that the smallest tubes on the kart happen to experience the highest cyclic loads (seat posts) and heat up the fastest during welding.
As for the repairs, we always had an acquaintance of ours with chassis welding and aviation welding experience tig repair them for us. We did 1 field repair at the track with a mig, but brought it home after the race and cleaned it out and re-welded. When welding would work slowly and pause some along the way and then wrap the finished weld. The focus was minimizing heat input and controlling cooldown since we could not perform any PWHT.
I don’t know of any other manufactured product especially in motorsports where this accepted as normal. There has to be a engineer somewhere that can say to OTK, do this and this won’t keep happening. Weld a flange gusset where the post is welded to the frame…i mean i would think that would fix it.
A kart frame is a bit unique in that it has ti flex and deal with a lot of vibration. A gusset or a sleeve could fix it. But does that risk affecting the flex of the frame and the handling?
Probably not, but I have to imagine there is a reason they don’t just put a gusset in there.
I thought about that with possibly changing the flex..maybe use spring steel from the gusset up the the seat mount. There should be a compromise. It seems like you don’t hear about margay having as many problems with this.
Margay uses bolt on seat struts as far as I’m aware. This issue isn’t stritctly OTK, it’s all karts with welded seat stays. On the Crocs we had issue with the tabs on the seat stays cracking until they changed how the tubing is crimped which has helped. They still occasionally break at the bottom where welded to the main tubes. I figure part of it is the stays are made from a cheaper/weaker material than the main tubes to save money. Some manufacturers played with brazing versus welding on the seat stays to keep from weakening the metal in the heat affected zone.
Weld it up and send it. Breaking a seat strut has become a right of passage int the OTK world. The only real issue lies in the mental anguish of ruining the powder coating. At least for me..
Agreed with all here. Had the same strut break on my 2023 Kosmic and never skipped a beat after the local shop welded it (can’t say I was all too satisfied with the weld either).
Hi Ryan. Good feedback from everybody here - it’s common and no need to overthink welding it. Also, I didn’t realize that you’re local to NJMP. Are you doing the Northeast Kart Challenge? It’s the local series to me and I’d be happy to help get you up to speed at one of the races.
