750 crank in 850?

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Apr 15, 2004
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I've been busy tearing down the 850 motor. Cylinders are at the machine shop getting a rebore. I sent the head out to get the exhaust threads repaired. I split the cases yesterday. It needs new bearing shells and a good thorough cleaning, but doesn't look too bad. I should probably replace the main bearings too while it's apart. I suppose I should split the crank so I can make sure it's nice and clean inside too.

It occurred to me that I have a 750 crank assembly sitting on the shelf, all built up and ready to go. I have new Superblends for it too. How do you guys think that would work in the 850? It's been balanced for 750 pistons (GPM) so the balance would be a bit different. Think that would be a problem? It would save me some time and a little cash (for now anyway) if could use it.

Debby
'72 750 Semi-Combat
'74 850 project
 

Ron L

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Feb 27, 2004
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Debby,
I don't think I'd try it. As you say, the 850 crank and 750 crank are balanced for different pistons. At the very least I would have the 750 crank re-balanced. That would probably negate any cost savings.

Other than labor, your cost difference is really only a set of rod bearings and rod nuts. You can use your superblends on the 850 crank.
 
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