Case Damage Question

[mandm]

I am in the middle of a rebuild and found a crack on the lower case on the outer portion of the crank bearing seat. Not sure how this would happen and I was trying to decide to TIG weld it up or replace the cases. Also noticed a lot of scoring on one of the other bearing seats. Any opinions?

 

[TwoManyXS1Bs]

Yeah, that's not good, for 2 reasons.

The crank's ball bearing fits there, located by the c-ring. It confines crank lateral movement.

The primary gears spin very close to that particular spot. Any welding would have to be ground completely down to regain that clearance. Do a search on "primary gears" to see some examples of scrubbing in that area...

 

[TLCbobber]

Probably caused by not lifting crank out squarely, lifting one end too much or lifting the crank and the case kinda stuck to it and got lifted too before it broke free at one side leaving it to hang on the crank at the other end. It looks really weak there, wouldn't take much crank tilt to crack it.
The top case half has the locating dowels, it's better to split the cases upside down, lift off bottom case then lift out the crank from the top case. With it that the dowels direct your lift a bit and kinda force a square lift, since they're ideally assembled upside down. strip and rebuild = reverse operations.

Any welding would take a fair bit of machining to fix mating surfaces and the ring groove. Cracks need to be cut out and have the ends drilled so they don't spread or recur. Personally I think this looks to be more trouble than it's worth. Someone might be pro enough to fix it but I'd try get spare cases, a matched pair and crack on. pardon the pun.

 

[Brian902]

If that is the scoring in the first picture and it's the transmission shaft bearing that was spinning I would be more concerned with that.

Is that bearing seized on the transmission shaft?

I would be tempted to break that small cracked piece of aluminum off and see how far it broke to. Then clean up the edges and continue. There is lots of groove left there to hold the bearing from moving laterally and the bearing area is not really affected. I'd use the cases if that was the only issue. The only thing I see that could happen to that cracked piece of aluminum case is it could break off later with vibration if left as is. So remove as much as you need to and continue. The other case has lots of cir-clip grove so no big issue.

It 's the grooving in the other bearing are that concerns me.