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  1. #1

    Join Date
    Jun 2007
    California, MD

    650 750 780 difference? What's interchangeable?

    This question concerns the Polaris-used blue Fuji engines...650, 750, and 780. These engines appear identical on the outside, but their displacement tells us there are (at the minimum) bore and/or stroke differences.

    What's the difference guys?

    We see casings, cylinders, heads, etc. advertised with 650, 750, and 780 headings. What is actually interchangeable? Do all engines use the same crankshaft? Casings? Are the heads identical? Can I bore a 650 cylinder out to obtain a standard 780 bore without getting dangerously close to the water jackets? What about a 750 bored to a 780? Any problems with porting here?

    I was hoping the pros could shed some light on what can be used as replacement parts.

    Thanks in advance!

  2. #2
    someone correct me if im wrong but i believe the only diffrence motorwise is the displasement in the cylinders. the stroke is all the same between all three. i think you can have the cylinders re-sleeved but not bored.

  3. #3
    650 750 jetting ,heads ,cylinders, pistons 750-780 case ( but u can retro any with mods ),cylinders heads,pistons jetting,carb linkage on some, and exhaust manifold ,oh reed spacers were std

  4. #4
    She likes the bike. But the ski gets her wet!!!! xlint89's Avatar
    Join Date
    Oct 2006
    Cleveland OH
    Crank is identical for all 3. Cyls are all different. 650 can't be bored to 750. 750 can maybe be bored to a 780, but it's not a true 780. I say that because 780's have an additional 2 exhaust ports the previous years didn't. The heads are not interchangable, but you may be able to make a 650 fit a 750 with some machining. 780 heads won't fit 750 cyls without enlarging the bolt holes in them, and vice versa. Carbs, reeds, intake manifolds are all interchangable. 650&750 Exh mans. are, but 780 are different. Cases are all interchangable, but 780 has 2 additional "ports" if you will in the upper case that the other 2 don't. Engine couplers will work on all 3. Elec. stators will work, but we are finding out some 650 may not fire CDI's. 750 and 780 stators are interchangable. Flywheels try to match with stators because of timing differences. Should be about it.

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