TOPIC:

Cast Aluminum Motorcycle Engine Case Repair

Hi all, I have no experience getting something professionally welded. I am looking for advice on repairing a shoddy repair to a 1985 Kawasaki GPZ 750 turbo engine case. At one point, it looks like the bike fell over on the right side and cracked the right side of the engine case, the part of the case that holds the pulsing coil. It’s a dry seal with no oil in it.

Picture 1 is of the damage. Regarding item number one, the previous owner must have removed the damaged section and installed this patch. It’s the wrong thickness metal and most likely does not provide a seal that would keep out the elements. It should look like photo 2. Also, the thread that holds the cap/cover bolts was removed. I bought a donor case, pictured in photo 3, would the best approach here be to weld a patch from the donor after removing the damaged piece?

Regarding item 2, as mentioned above the previous owner removed and tapped out the  original thread. It should look like something like the circled area in photo 4 and 5. What is the best way to repair this thread so that I can use the original hardware? The owner used longer thicker bolts to hold the cover/cap on. This bike is a restoration project, so I’m trying to make it look as factory as possible. I figured for the thread in repair 1, he could just use the thread from the patch from the donor motor. These threads just hold on a cap/cover, not much torque. 

I plan on taking it to a professional, just would like some perspectives on how a welder would approach this.

additional photos below

Additional photos mentioned in initial post

Additional photos

Depending how "oversized" the lower bolt hole is you could use a "helicoil" or "time-sert" to recover the original bolt fitting. With the casing repair it should be possible to insert a patch from the donor with the mounting point intact. (I would suggest supplying the welder the top and bottom casings bolted together to reduce the risk of distortion during the welding process)
If you repair the lower thread first you could bolt the cover to it and the patch to ensure correct alignment

Is it just the lower hole or part of the case too? I've used m8xm6 inserts on munged up holes found on eBay. 
Steve

The bottom damage is just to the thread/whole, no damage to the case. I was thinking of having a welder tack some material on it and then drill and tap a new hole for the bolt. For some reason the previous owner removed a lot of the thread, the thread should not be that far back. 

If I remove the pickup coils for the welder to make repairs and then put them back on, will that mess with the timing? Sorta inexperienced with bike restoration, but learning

I'll suggest try a repair with JB Weld epoxy and helicoil for the threads. No need for welding that way. Epoxy won't adhere to the non-sticky side of cellophane tape. You could try to get some tape in there to form a shape for the epoxy then peel it off after the epoxy dries. Then just file/sand the epoxy to the right shape.

My opinion for what it's worth is to patch the upper casing with the donor. If you Are going to the trouble of restoring the bike then it would be a much better repair (if done correctly) than epoxy 
You will need to set the timing afterwards but it's not difficult

Thanks Wookie, I plan on using the donor. Hopefully will have results on Saturday.