Broken case...

[250motoxer]

I need some advice... I was riding on Sunday and my chain broke!!! The chain ended up getting jammed in between the front sprocket and something else(not quite sure).... But anyway, I noticed the back of the engine case around the pivot point for the swing arm is cracked. Can this be welded? What do I do? Thanks in advance for any ideas... 1989 (oldie but goodie) KX250.

 

[CRguyStan]

The cases are usually made of an aluminum alloy that is great for casting, but when heat is applied such as to TIG weld, the metal puddles away from the heat. Therefore, I have never had much luck with welding any case parts. If the item is cleaned JB Weld can sometimes bond quite well, but the location you speak of is a structural point to locate much of the bike together. This will likely never totally shatter apart, but will pull apart some causing an endless oil leak and potentially some transmission tension. I would start searching for a blown motor to throw your top end on for a few bucks.
Stan

 

[Jim G]

go to your local welding supply store and look for a product called "Lab Metal". You will need the lab metal paste, and the lab metal thinner. Use as directed. This is some incredible stuff.

 

[Ol'89r]

Like Stan said, the aluminum used for cases is not the easiest stuff to weld. But, it can be done. The trick is to clean and boil out all of the impurities.

The case has to be very clean and the crack must be ground or 'VEE'D' out down to clean metal. While welding, you may have to go back and re-grind the impurities out and re-weld. As you weld, the impruities will rise to the top. Any good tig welder should be able to do it.

The main difference is, JB weld is temporary and welding is permanent.

Good luck. :thumb: