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  1. #1

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    97 pro 785 top end rebuild info needed

    Hey guys, I'm in the process of buying the parts needed to do a top end rebuild on my pro. I've decided to use the 750 pistons and I was hoping someone here could enlighten me as to what else would need to be done to get these pistons to work correctly. Just so everyone is aware my jugs have been sleeved by the previous owner, will this be an issue?. Some of the questions I need answered are
    1. What brand 750 pistons to buy?
    2. What rings and wrist pin to use?
    3. What piston to cylinder clearance to use?
    4. Any port timing work need to be done
    5. What head gasket works?
    6. Anything else I may need to know


  2. #2
    750 as in same size as the SL 750? Im new to these motors, I was just curious what the benefits of that would be?

  3. #3

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    Yes from a sl750, from what I've been reading so far they are a good inexpensive alternative to the OEM or wiseco 785 pistons.

  4. #4
    Moderator beerdart's Avatar
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    Yes the SL 750 fits if the 785 is a stock bore.

  5. #5
    urugol's Avatar
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    Difference is in the stroke which is where you get the different displacement between the 750 and 785 stock engines.

    WSM makes a decent piston kit. Don't bother with the complete piston kit as your gaskets are different you should source those separately.

  6. #6
    She likes the bike. But the ski gets her wet!!!! xlint89's Avatar
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    Quote Originally Posted by Recniz View Post
    Hey guys, I'm in the process of buying the parts needed to do a top end rebuild on my pro. I've decided to use the 750 pistons and I was hoping someone here could enlighten me as to what else would need to be done to get these pistons to work correctly. Just so everyone is aware my jugs have been sleeved by the previous owner, will this be an issue?. Some of the questions I need answered are
    1. What brand 750 pistons to buy?
    2. What rings and wrist pin to use?
    3. What piston to cylinder clearance to use?
    4. Any port timing work need to be done
    5. What head gasket works?
    6. Anything else I may need to know
    1. Get the WSM 750 STD size unless your sleeves have been bored oversize.

    Q: why are you replacing the top end? Was there damage to the previous top end? Do your cyls need to be bored?

    2. The ones that come with the piston kit

    3. Whatever the manual calls for on the 785

    4. Not because you're using 750 pistons. But if you start installing larger (oversized) pistons, you're altering your port timing (the cahnges are minimal, but you are enlarging the port sizes when you remove material from the sleeve)

    5. 785 head gaskets only, unless you have aftermarket heads, or had the stocker machined for O rings.

    6. Yes, get your hands on a repair manual. You'll need to know bolt torque specs and tightening sequences.

    Lastly, temp. install your cyl head before you tighten the cyl base nuts. (cyl alignment)

  7. #7

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    Quote Originally Posted by xlint89 View Post
    1. Get the WSM 750 STD size unless your sleeves have been bored oversize.

    Q: why are you replacing the top end? Was there damage to the previous top end? Do your cyls need to be bored?
    I had severe cold seizure on all three cylinders plus the PTO only have 30psi and was leaning out bad adding to the troubles. Once I get my parts I'll be sending the pistons and jugs out to the machine shop to set them up to factory specs.

    Two more questions for you guys.
    1. who has the best deal on the pistons? so far I found them for $68 each, is this good?
    2. Can someone recommend a top end gasket kit and a place to buy it?

  8. #8
    I'D RATHER SWEAT THAN SHIVER hyoctane23's Avatar
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    I recommend Comedic for the gaskets. They seem to be of good quality.

    http://www.cometic.com/

  9. #9

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    Quote Originally Posted by hyoctane23 View Post
    I recommend Comedic for the gaskets. They seem to be of good quality.

    http://www.cometic.com/
    Would you know if the c6181 kit comes with everything needed to do all three cylinders???

  10. #10
    I'D RATHER SWEAT THAN SHIVER hyoctane23's Avatar
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    It comes with every gasket you need for all 3 cylinders except for the crankshaft seals. You will have to buy those separate if you're cracking your cases. I would call them first and be sure that is the correct part because the website shows that it is a 72.0 mm bore and that isn't correct. I would also go on and buy a few extra exhaust valve gaskets for when you clean your valves down the road because they are a LOT cheaper than trying to use OEM Polaris gaskets.

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