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617/618UL Big Bore Option

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Armilite

Well-Known Member
Joined
Sep 5, 2011
Messages
3,738
Location
AMES, IA USA
I saw this AD on FB the other day where a guy put 670, 78mm Cylinders on a 617. So (78mm x 68mm) 650.1cc. 670's have been Big bored to 82.5mm. (82.5mm x 68mm) 727.3cc. Not sure yet what all he did to accomplish this. You have the (617) 76mm vs (670) 78mm Bore, the (617) 68mm vs (670) 70mm Stroke, different Top Rod Bearings, and (617) 125mm Rods vs (670) 132mm Rods. Skidoo 521's and 617's were all Provision 4 Cases. Would be a better setup if he could have put a 617 Crank in a Provision 8 Case. He has a Good Price on them. Stock 582UL (65hp), Stock 618UL (73.4hp), Stock 670 (95hp). Lots of 580/582/583/582UL Provision 8 Cases out there.

Has anybody ever done one of these conversions?
 

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