.080. overbore .

Torontonian said:

Wear . 850 pistons and bore were worn out at .040 . Gord Bush Performance called to say I need to order in .060 pistons to them for the new rebore . Jim has ordered forged pistons in for the springtime , as I will be exploring west Africa with my wife .

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There are 2 sets of 850 +.060 on Ebay, link above. $60 or BO.

FWIW, I've successfully built a couple of Commando engines with 850 cylinders bored out to 79.5 mm (+ .100 in), but not all 850 cylinders will take that. In your case, you should be fine with the 78.5 mm (+.060 in) that you have ordered from Jim. I've used 78.5 mm pistons in 850 cylinders in a short stroke race engine with no problems.

Ken

If I was replacing pistons. I would struggle through the Mahle catalogue,