Vintage Dirt Bike Q & A

I'm working on my 74 CR250. I've have an air leak which I've traced to a crack in the engine case. The crack in the case was caused when a rock or something must have become wedged between the front chain sprocket and the engine. (At least that's my best guess) The case has a slight crack near the clutch post.

My question, has anyone tried to weld the case on this engine. I do have access to a alum welder, and I'm planning on giving that a try, but wanted some input as to any other options. It not a large crack, I could use JB weld, or other product, but If it can be welded, I would prefer to go that route.

thanks for the help.

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74 CR250M, bought new in 74, still stock, except for the new 36mm Carb, and proform exhaust.

I sold one of these back in '75 after I threw a chain through the case. My neighbor bought it and used JB weld. Held great so if you have to do it, just clean it really good first. As for welding, I don't know if it is alum or pot metal.

The cases on these bikes are magnesium. They can be welded by someone who knows how to weld the stuff. I broke off the small part that holds the clutch cable on the right side case on my mr. A welder friend of mine t.i.g welded a lump of weld on the case. Then i ground it back to shape.

The cases are aluminum, and the side covers are magnesium on the 250M's, get your local weld shop to put a bead of aluminum were the crack is and grind it smooth to shape.