ATC250ES frame down tube repair

[TheRadBaron]

I recently bought a pretty nice '85 250 Big Red. It's all original and in good shape, except the frame was badly broken on the front down tube below the steering head. It had been really poorly repaired by welding some steel square stock on either side of the break, but the frame was so badly twisted that I figured it couldn't be made right again. I guess the PO tried to ride it out of the back of a pickup truck and FAILED.
I bought a used '86 frame that was supposed to be a "really nice frame", but when it arrived I found that it had been cracked and repaired in almost exactly the same place. This break must not have been nearly as violent as the first frame, though. The down tube was still aligned perfectly, and there wasn't any twisting or damage anywhere else. The weld repair was even of okay quality. I decided that I'd try to make this frame work. I got some of my money back from the seller, too.
Since both frames were broken in close to the same place, I figure that this is a common problem and maybe a weak point of the frame. Since I'd be repairing the frame anyway, I figured that I'd reinforce it while I was at it. I took some pictures as I went along, so hopefully this can be of some use to someone who has the same problem.
Here's the frame after I ground the weld repair down flush with the frame tube. The weld was actually pretty sound, but it was still certainly weaker than the frame was originally.
http://i65.photobucket.com/albums/h219/blackguard77/IMG_2125.jpg
These are the repair plates that I made to go around the tube. It's DOM steel tubing, 1 5/8" OD, .120 wall thickness. The ID is almost exactly the size of the frame tube. I cut it in half with a bandsaw and drilled 3/8" holes for plug welds.
http://i65.photobucket.com/albums/h219/blackguard77/IMG_2127.jpg
Here's the repair tube mocked up on the frame. The plan is to weld both sides up the spit in the repair tube. There's about 3/32" gap between the two tube halves, so the weld bead will penetrate the frame tube and also join the repair halves together. The holes in the repair tube will be plug welded to the frame. Also, the tops of the repair tube will be welded to the sheet metal stamping around the steering head.
I thought about it and decided not to weld the top and bottom edges of the repair tube to the frame. I think a weld there would actually weaken the frame at that point. There's techniques to avoid that problem, but I think it will be plenty strong as-is.
http://i65.photobucket.com/albums/h219/blackguard77/IMG_2128.jpg

I welded it up with my 135 amp Hobart MIG welder, using .030 wire and 75/25 shielding gas.
I finished up the repair tonight but I forgot to take pictures. It turned out really well. I'll post some pictures soon.

[dustrunner]

hi, have you ever welded before. i do it everyday ! if weld is done right it is stronger than the original metal. i would weld over what you have and grind it a bit and paint it and be done but thats me.. if you feel the patch will work better than go for it just make sure the exhaust wont rub on it.. good luck..

[TheRadBaron]

Thanks. I haven't had any formal training in welding, but I do a lot of it on various projects and things around the house. Everything that I've read about welding and chassis fabrication leads me to believe that simply butt welding tubes together in high-stress areas isn't the best idea. An example is when extending a swingarm, it's common practice to back up the welded areas of the extension with tight fitting slugs or tubes that are fitted into the ID of the swingarm and extension tubes and extend a few inches past either side of the weld, then the weld is made on over them. Since I didn't have access to the inside of the frame down tube to insert a back-up tube, I decided to go on the outside.
Plus, this method of cutting a tube in half and welding it around a cracked frame tube is an approved way to repair aircraft airframes. I'm not 100% sure about it, but I don't believe that simply welding up the crack is approved. At least not when a better option is available. If it's good enough for an airframe, it'll work on a 3-wheeler.
The exhaust clearance issue is something that had occurred to me. I haven't test fitted it yet, but if there's a conflict I'll just reshape the repair to make some clearance.

[segers200s]

thats nice job there with the plates rather then just a weld cuz if it broke once it will break on the side of the weld so plating the tube would be the way I would go lot more stronger then a weld by its self I like it never break there again good work

[WilliamJ]

Enlarging the size is the right thing to do. Plugging is a good way of retaining two layers together but nickel bronze would be my first choice. I would cut the damaged section out then put in a larger diameter tube and overlap it onto the original tubes top and bottom. The nickel bronze would give a very strong joint where it flowed into the gap between the sleeved sections.

I suggest pre-heating the MIG weld area to reduce the chances of embrittlement close to the weld. Particularly where the large repair tube stops and the original tube begins.

If you can borrow one use a TIG welder.