How would you fabricating experts fix this???...

Picked up a Moto Ski Ltee frame over the weekend and it's got a hell of a crack through about 75% of the frame tube. It's right where the engine plate was welded and I didn't notice it till I got home. My first thought was to get something inside the tube to support it then weld it back together, however that would mean I would have to cut the tube completely (in possible 2 spots) and I just dont think that's the right play... I did cut and grind away the corner of the engine plate after I took the pics to have good access to the crack all the way around. Only thing I can come up with at this point is to just weld the hell out of the entire crack and call it a day? :shrug: Do you think that will hold up? Full disclosure this will be the second time i've ever welded, good news is my pools are still way too big so at least I know I'll get good coverage on the crack! :thumbsup:

Side question: how do you get your pics to be thumbnails that open the view window when clicked? (yes I searched and searched)
Find you a piece of pipe that has the ID of the frame tube. After welding the crack and smoothing it out place a splice( half piece length wise) of the new tube/pipe on the inside bottom to reinforce the frame. This way its not as noticable and will allow you to monitor the frame if it should crack again.


Growing up is optional
Unfortunately (don't you hate sentences that start that way?!) To fix it right, you would have to cut it up, or just about rebuild it. So you could do this. Clean the crack down deep with a cutoff wheel and suck the two tubes together the best you can ( a come-a-long will work great!) and weld em together. This will hold up for a while, but will eventually crack again. So, what you can do after it's welded, is turn it over and slot the bottom parallel with the tube to fit a piece of one inch by three eighths flat stock about four or five inches long and insert the flat stock in all the way to the top of the tube, and weld it solid on both sides. Then grind the excess off only to the top of the weld. Make sence?
The frame cracked from fatigue due to loads (rider, bumps), and vibration from the motor. Even if a professional welds it, it won't be 100%. It may be fine for putt putt, but I would go to the next level if she's a keeper. This means cutting the whole ass off the bike, then plug welding some dowels in, and stitching it all back together. Good luck, I've got the same prob with my go kart. :hammer:


Active Member
weld it, grind a wide V groove in the crack to give the weld space to fill in. then weld something to the bottom across the crack to support the tube.
Aside from cutting out a small section and using an insert, the easiest and least expensive thing to do would be to clean it real good and weld the snot out of it and grind it smooth. It may or may not last, depending on you riding style. Good luck. :thumbsup:
You have some good suggestions to go with, the only thing I would caution is watch your heat. Where you get your supplies let them know what your doing and the gauge of the tube -see what they suggest for rod and amperage.

You may want to practice on some scrap, its going to be real easy to melt it.
well you said the crack is 75% well take it 100 cut it around . the frame mite pop apart when you cut . but you could push the tube to the side and slip in a plug with a little sticking out like 3/4 inch :shrug: run a weld in a hole to the plug locking it in place . then push and pull the frame back and finish welding the mess .
well you said the crack is 75% well take it 100 cut it around . the frame mite pop apart when you cut . but you could push the tube to the side and slip in a plug with a little sticking out like 3/4 inch :shrug: run a weld in a hole to the plug locking it in place . then push and pull the frame back and finish welding the mess .
I agree with MM if its already broke might as well do it right


Active Member
Cut it clean, place a 1" or 2" all steel slug inside the tube, pull the tubes back together leaving approx. 1/8" to 1/16" gap, weld it and blend the weld with a sander.
If cutting the frame isn’t an option….use “fish plates”. As others have said….first clean & weld the crack. Shouldn’t be any need to open the crack up…the problem will be to keep the weld from blowing thru too much. TIG would be best, but you’ve probably got some major rust inside the tubing…which will cause a major pain with TIG. I would suggest running it with MIG, small diameter (.025-.030”) E70S-6 wire, and will probably be the simplest to run. You could even gas weld it with an Oxy-Acetylene rig and a small heat tip but the heat input would probably destroy the strength of the tubing. It’s do-able with 3/32 DC stick rod….but very tricky. Smooth off the surface of the welded crack, then fabricate a fish plate diamond from metal plate or tubing about the same thickness as the frame. I’d probably make two, one for each side. Looks like the inside one would need to be notched to fit over the cross member. Diamond shaped fish plates work better than rectangular ones. Form it to fit the contour of the frame tube. Again, clean the area to be welded and tack the fish plate in place…then weld. Try welding just a bit at a time…then let it cool to keep the heat input down. I’ve done this plenty of times to reinforce problem areas. Just make sure the fish plate is plenty large to cover past the cracked area. The trick of fish plates is that the stress force is now applied at angles to the crack, rather than directly on the crack. For those not familiar with the term “fish plate”, do a search for “welding fish plates.” Not to be a smart A--, but the real trick here is one’s skill to produce a sound weld on thin gauge tubing without blowing bigger holes in it. While it fish plates may not be the prettiest… it will work. When properly done…a weld is stronger than the parent metal…..underscore “properly”.

Good Luck,


Hoke, You are 100% right on the money. I agree that oxy-acetylene with a small tip would be the way to go....if anybody still knows how to do it. When I was younger I used to weld airplane fuselages with oxy-acetylene. The wall of the tubing was .035" which is about as thick as a hacksaw blade. The trick to maintaining the strength of the tubing was to finish the weld and then continue to apply heat to the weld and to the tubing on each side of the weld while slowly backing the torch away. This "annealing" allowed the weld and the surrounding area to cool down slowly and thereby maintain its strength and integrity. The fact that there are thousands of airplanes built in the 1920's, 30's and 40's with tens of thousands of hours on their fuselages still flying today is a testament to the dying art of oxy-acetylene welding. Ogy
Hey Ogy....don't forget all the car exhaust that were gas welded with coat hangers. ha And you are correct....slow cool is the only way to go! One of the first places I worked...many moons ago, required a Oxy-Acetylene test on top of Mig & Tig qualifications. Fortunately, I had some old timers (back then) to teach me. Also, before the days of custom built hot rod plates were the way to go when chopping a frame.

just make the second cut and put slugs in. Cleaning up that second weld will be easier and neater than anything else I think. To get it nice and smooth after its welded I grind it down then finish off with a nice wide file. then fill in any low spots and file it again. good as new :thumbsup:
oxy-acetylene ahhh my first welding was done on one :thumbsup: another thing about using that if the crack has legs the heat will show them and you can chase the crack with the torch .

Bird Brain

Active Member
Bevel, slug fit, and perhaps a gusset where it allows would be the only way to keep what you got period correct, otherwise i agree a partial rebuild with new material would be the stronger option.


Active Member
I think it's great when people talk about OA welding - I learned this many years ago, and it's an excellent method for thin wall tubing.
I find it very controllable, and with a small tip, and practice, you can do pretty precise and clean looking welds on very small parts.

NOW, I've bought myself a TIG welder, and I'm trying to teach myself that - Talk about a steep learning curve !
In a way, it's like OA welding, as far as it's using a separate torch and filler rod, but WAY different otherwise.......