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Let’s look at the logic and facts And options. 1. You can’t drive it like that. 2. A good welder might be able to fix it but probably not after you put on JBWeld. 3. JB Weld putty stick might work. I fixed the bottom of my crank case last year and it’s still holding. Not as bad as yours. 4. New engine.
If a welder can’t help, or you can’t find one, or don’t want to, I’d try JB.
Take off the chain and gear to give yourself room to work. Clean the area really good. Sand where you want it to stick. Clean it with alcohol, not tequila. Make a ball into a pancake with the putty and slap it on good. Don’t plan on it being pretty, you won’t have time to do that. The putty hardens FAST. Practice with a marble sized ball first so you can see what it does.
You can see I had to cover a bolt to hold it in. I put a slice of scotch tape on the exposed shaft of the bolt so the putty wouldn’t stick to it in case I ever have to crack the case. This is the under side of the engine. I hit it on the trailer ramp picking it up from the seller. I cried for a while but then I fixed it. I was pretty lucky.
Good luck and Best,
Steve
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Yeah. Ok. Just my 2 cents on something to try before spending a bunch of money. I didn’t see mention of the missing pieces in the original or subsequent posts. If he can find a welder/machinist who can fix it that’s great. If my choices were buy an engine or try jb weld, i would try it first.
Best,
Steve
 

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You're talking a solid patch some 2 inches wide X maybe 4 inches long, there is no such survivable epoxy patch on earth that can do that. If the pieces aren't there even the best welder on earth will pass on the work, there is too much material missing. Looking at enough heat replacing it to warp nearby surfaces, the last thing you should be doing. The split line crush stress alone wrecks the idea. That area is already a known weakness point on SOHC 750 cases, they broke plenty of them there.

I've both welded and epoxied race heads at $20,000 each to recover them to use again; I got a pretty good idea of what will work and what won't.
So you think he needs a new engine?
 
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