welding crank case

[Moshi]

hey,
I recently messed up my crank and the lower conrod knocked against the crank case, causing it to crack on the one side and knock off a small piece approx. .5x.5cm on the other. Does anybody have experience fixing things like that by welding? I have a guy here that's gonna weld it using argon welding. Any advice before we give it a go would be much appreciated.
Moshi

 

[dirt bike dave]

There was a post awhile ago about this - I think Ol'89er is experienced with this sort of thing and may be able to offer advice.

FWIW, on the Honda CR250, the crank case halfs can be purchased separately and are not too expensive as motorcycle parts go. I think I paid about $160 and the new crank half includes a crank bearing ($30+) which you will probably have to replace anyway.

 

[Ol'89r]

Does anybody have experience fixing things like that by welding? I have a guy here that's gonna weld it using argon welding.
Moshi

Moshi.

I take it he is going to tig weld or heli-arc your case? If so, make sure the case is very clean. Clean it with a solvent and then clean the area to be welded with lacquer thinner or acetone. Take a rotary grinder and grind the area back to clean metal. On the crack, grind a vee about 3/4's of the way through the crack, then using filler rod, weld it back up. A 4043 filler rod works very well. If your welder is experienced with welding aluminum and doesn't use too much heat, there will be no problem with warping the cases.

After welding, use a rotary grinder or flat file to reshape the mating surfaces of the case at the weld. Or better yet, have them milled if you have access to a machine shop. Also, make sure the weld bead doesn't stick up too far inside the cases where the flywheels are. There is very little room between the flywheels and the case so, you may have to grind down the bead to clear the flywheels.

Good luck.

 

[Gibby]

Sounds like a knowledgeable welder for once. Good luck

 

[Moshi]

I think it will be a tig welder. he is giving it a go as I write. Am a little nervous, the nearest honda dealer that sells cr spares is probably 5000miles + away.
But thanks for the advice! this forum has been invaluable to me these last couple weeks.