Swap casings

[barnfind]

Is it a good idea to swap top casing where the cylinders are onto a different bottom casing. The reason I ask is because my bottom casing is smashed where the chain sprocket is....chain came off a high speed and well... Did some damage. Is the original cases machined together is this a bad idea ? I think the bottom case can be fix,it's just going to be a big job. I have a number matching  1969.

Thanks

[TOOLS1]

They are machined together, so replacing one section is a bad idea. When you separate them, you can see where the factory marked them as a set after they were machined.
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[barnfind]

That's what I figured.

Thanks for the help.

[TOOLS1]

You know, now that I think about it. I wonder just how close Honda was in their machining? A seller on ebay (MrMonkeyclaw) right now has a set of sand cast cases for $45.00. The top case was pretty badly damaged, but the bottom case looked good. Foe $45.00 it might be worth testing the fitment.
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[barnfind]

I'll look into it.
Thanks

[Re-run]

Do you mean the cylinder jugs onto a different bottom? Cause that would just mean a new gasket and that's all.

Otherwise, I thought the bottom was split into halves on all the sohc engines. Top half and bottom half. Then you would just need a good side for the left side of the engine and some 3 bond or hondabond sealer.

Nothing on these engines was really machined together where you can't swap things around. About the only real issue would be the heads since later engines had changes to the oil passages.

however, I suppose being matching would make it a different story if you wanted to keep the numbers. I would just get a different bottom since I don't think there are any numbers there. Or fix your case unless the damage is really extensive.

But then, if it is a sandcast, maybe it assembles differently than all the later engines.

[TOOLS1]

He is talking about the cases, not the head/cylinders. They split horizontally, not vertically like Harleys, or British bikes. The cases were bolted together at the factory, and machined as a set. When you split them, you can see the markings where the machinist  marked them as a set. That why I was wondering how close Honda machined these cases. If he had a good bottom case to test fitment with, it might be close enough to use. It would need to be bolted together, and carefully measured to see.
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[Re-run]

Oh yeah, duh. Still, they were not machined that closely. It may be that the mating surfaces might need to be smoothed out a bit but even that shouldn't be an issue. The cases just used hondabond or 3bond so any gap should be sufficiently filled unless it is a big gap.

My only concern would be be if he has a sandcast or 69 die cast, that he would want to keep the halves from the same type of engine.

I think bearing surfaces might be more of an issue than the mating surface. I know people have swapped bottoms and not had issues but I think they stuck close to their year of engine, i.e. 71-76,  77-78, and so forth.

Though, I think I would just try to patch the case he has, unless the damage is really bad. Hard to say without a pic.

[TOOLS1]

I doubt the mating surfaces would be any problem. It's the bored holes for the crank bearings, and the transmission shafts that I wonder about. The seller I told him about on ebay does have a set of sand cast cases, but the top case is badly damaged. The bottom case looked useable though.
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[Re-run]

If this wasn't a 69, I probably wouldn't even worry about it but Honda wasn't sure how well it would go over so it may be possible they may not have the same measurements from engine to engine.

That's the danger with riding a 69, damage may or may not be harder to repair.

[barnfind]

Thanks for the info guys.