09 yz450f chain broke, cracked case...Is it repairable?

Was riding this weekend, came down off jump and chain broke...had the stock case guard on which did nothing and now have a crack right at the clutch shaft. Can this be welded or do I have to replace both cases?

Was riding this weekend, came down off jump and chain broke...had the stock case guard on which did nothing and now have a crack right at the clutch shaft. Can this be welded or do I have to replace both cases?

Can you upload a photo so we can have a close look?

I have had good success welding these magnesium cases with AC TIG, but depends on the severity and positioning of the crack/smash.

...depends on the severity and positioning of the crack/smash.

More so than usual with the YZF, because oil pressure to the trans is fed right past the clutch release arm.

i welded that on a crf450 once

A good aluminum welder should be able to fix that up for you.

Would you have to split the cases and weld from inside? or can you do it from outside?

Split the cases for sure or you run the risk of damaging seals etc. with the heat. But I think welding from the outside should be fine.

It's really going to depend on how things turn out. You can attempt that repair from outside, although I would plan on replacing the output shaft seal and the clutch release arm seal. You should also remove the clutch pressure plate so that you can draw the push rod out of place and pull the release arm up and out during the weld operation. Then see if the arm goes back in and rotates smoothly. There is a bearing below the seal that could become misshapen or otherwise damaged if the heat is too great or the bore distorted. I recommend using a welder who is also a machinist so that he will better be able to appreciate the situation.

It's hard to tell where exactly the crack is, but it doesn't look too bad from what I can see. If I'm right about that, the repair should go fairly well.

If the arm and shaft is steel you should be able to weld the outside with the shaft in there so it will be able to maintain its shape. I did it once on a 06 YZ 250 and it worked and mine looked a lot worse than that.

mine was way worse also...i caught a rock on me year chain guide and it sheared off, threw the chain into the cases as it hopped off the rear sprocket. it went dead stop...my tranny shifter inside the cases broke, my chain guide was sheared off and the swing arm, and i broke the case saver off that mounted to the cases and sheared that portion off. your in WAY better shape than i am.

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