who'd like to see my crack

stripping my 920 race engine to fit new liners I took the oppertunity to repair my PTO shaft to stop the bearing spinning, There wasnt enough metal to grind the 0.060" radius so I had it laser welded; Then I thought it a good idea to have the crank crack tested and guess what ,it was cracked. Thinking I had a suitable spare turned out out a non starter as the previous owner had removed( butchered) the bearings off with a chisel and caught the PTO. Does any of you budding Metalagists out there know if building up the crank with weld will provide a fix ( and the appropriate radius ) or am I just screwed?
I have tried to attach a copy of the crack testing report with a picture of the offending crack , if it doesnt work then accept my apologies and let me know how to do it properly.

Moto55UK said:

I have tried to attach a copy of the crack testing report with a picture of the offending crack , if it doesnt work then accept my apologies and let me know how to do it properly.

Click to expand...

Yes, it works.

Ugh!

At least you found it this way and not at 7000rpm!!!
Good catch

Moto55UK said:

stripping my 920 race engine to fit new liners I took the oppertunity to repair my PTO shaft to stop the bearing spinning, There wasnt enough metal to grind the 0.060" radius so I had it laser welded; Then I thought it a good idea to have the crank crack tested and guess what ,it was cracked. Thinking I had a suitable spare turned out out a non starter as the previous owner had removed( butchered) the bearings off with a chisel and caught the PTO. Does any of you budding Metalagists out there know if building up the crank with weld will provide a fix ( and the appropriate radius ) or am I just screwed?
I have tried to attach a copy of the crack testing report with a picture of the offending crack , if it doesnt work then accept my apologies and let me know how to do it properly.

Click to expand...

I've blown up the picture a bit..

Nice welding job though all the same - not that that's any consolation

It looks to me like the crack you have is a bit too serious for weld repair, but I can't be sure. If you can still find a shop that repairs crankshafts with the right sort of wire welding lathe, and who are willing to deal with small motorcycle crankshafts, they should be able to tell you if it is repairable. When the crack is just around the circumference of the base of the shaft, and if it doesn't got too deep, it is certainly possible to repair. The problem is finding a shop willing to do so. I was fortunate to find one locally back in the late '70s to repair the crankshaf on a short stroke 750 in my race engine. It was a factory race crank, and had already had the radius ground at the mainshaft-to-cheek angle. The crack was part way around the shaft, right in the center of the ground radius. The crank shop I was using back then was able to cut a groove all the way around the shaft until reaching the bottom of the crack. They then filled it with weld using their automatic crankshaft wire-feed welder, and reground it to a .090" radius. I ran that crankshaft in the race bike for several years, until it was finally destroyed in an engine blow-up at Daytona in '86. Even then, the welded area was still good. I don't know much about this type of laser welding, but you would still have to groove out the crack before building up the area.

This is a picture of the S750 crankshaft after welding and grinding. you can see how far out the welded area extended into the cheek.



Ken

Ken

First off thanks to Cliff for blowing up the picture , Cliff the go to I.T . guy.
I could make a joke about me only being able to blow up the motor !
I dont think I made it clear that the the proposed repair is to the spare crank I have with the chisel damage to the PTO. when I had the previous crank laser welded the guys talked about deeper penertration so thatain when it is ground the weld still has enough metal to retain some strength. Following Kens reply I'm feeling better about having the Plan B crank welded. The proposal would be to have the standard crank cheek crack tested then laser welded, have the radius reground then tuftrided and finally balanced. Ken I like the look of those crank Bolts , where would I source those from.

Moto55UK said:

First off thanks to Cliff for blowing up the picture , Cliff the go to I.T . guy.
I could make a joke about me only being able to blow up the motor !
I dont think I made it clear that the the proposed repair is to the spare crank I have with the chisel damage to the PTO. when I had the previous crank laser welded the guys talked about deeper penertration so thatain when it is ground the weld still has enough metal to retain some strength. Following Kens reply I'm feeling better about having the Plan B crank welded. The proposal would be to have the standard crank cheek crack tested then laser welded, have the radius reground then tuftrided and finally balanced. Ken I like the look of those crank Bolts , where would I source those from.View attachment 81397

Click to expand...

this crank is still reusable after a weld repair if the NDT doesnt find an hidden cracks, and they can surely face up the PTO shaft as well.

looks like that gluteal crevice needs a wiping