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  1. #1

    Polaris 750 SL cylinder boring question

    I've done some extensive research on this Fuji engine.. and with that I have read some conflicting info. I have a project ski I got for dirt cheap and it has all the typical issues the ski's had. My number three cylinder had serious blow by and piston scoring.. the cylinder actually does not look bad but the amount of slap is obviously a problem. How much can I hone or bore this cylinder before having to re-sleeve it? I've read it can't be bored much at all.. plus I've read the wiseco forged pistons tend to seize. I would truly appreciate any info. I've tried to do a search on this in the forums but so many topics come up and so far none answered my question.

    Amazingly enough with all the scoring and blow by the compression test was equal among cylinders and was at about 95 psi.. my middle cylinder looked normal. Some how I have water in my crank case.. not sure how that happened this thing has not seen water in 4 years. Not a lot of water but enough that you can see droplets on the crank.

    TIA


  2. #2
    Quote Originally Posted by Didz View Post
    I've done some extensive research on this Fuji engine.. and with that I have read some conflicting info. I have a project ski I got for dirt cheap and it has all the typical issues the ski's had. My number three cylinder had serious blow by and piston scoring.. the cylinder actually does not look bad but the amount of slap is obviously a problem. How much can I hone or bore this cylinder before having to re-sleeve it? I've read it can't be bored much at all.. plus I've read the wiseco forged pistons tend to seize. I would truly appreciate any info. I've tried to do a search on this in the forums but so many topics come up and so far none answered my question.

    Amazingly enough with all the scoring and blow by the compression test was equal among cylinders and was at about 95 psi.. my middle cylinder looked normal. Some how I have water in my crank case.. not sure how that happened this thing has not seen water in 4 years. Not a lot of water but enough that you can see droplets on the crank.

    TIA
    Well as much research as I could without a manual.. guess I'll google a shop manual.

  3. #3
    BlueFishCrisis's Avatar
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    You can bore up to 1.00 over, I believe. It may be more beneficial for your to send your Jugs to SBT and do a top end swap.

    Water in the crank case is not a good thing......

  4. #4
    Quote Originally Posted by BlueFishCrisis View Post
    You can bore up to 1.00 over, I believe. It may be more beneficial for your to send your Jugs to SBT and do a top end swap.

    Water in the crank case is not a good thing......
    Thanks for the input.. yeah i thought about the swap... I may but I prefer to do things myself for the sake of feeling like I accomplished something lol. No rust in the engine.. its been out of water and covered with a tarp for 4 years.. actually.. i think typing this made me realize what its from.. pressure washing the rear of the ski before tearing it down.. possible to get water in thru exhaust.. guess so.. duh.. I feel like an idiot.

  5. #5
    skyboy's Avatar
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    Didz, not a Fuji engine guy but I have seen pistons from 70 mm to 72 mm in .25 mm increments. Plus if you do your own machine work, you can buy used cylinders and recondition them. That's what I do with my 700 engines.

  6. #6
    RLACEMAN's Avatar
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    If you can do your own boring, you may want to do that & yes Wiseco's do seize rather easily. From what I am told is the material they are made of expands faster under heat than regular pistons, & a couple extra thousandths of cylinder to piston clearance is required If you don't have the equipment to bore, then go the SBT swap, you can hardly buy the parts & do it yourself for what they charge + they usually include gaskets with those kits too.

  7. #7
    Standard bore is 69.75 mm. Wiseco has 5 oversize's, up to 72 mm. The piston kit comes with top end gaskets. My husband just had our youngest daughter's 750 engine bored by Bill Bune Enterprises in Anoka , Minnesota. If you buy the pistons from him and have him bore them it should cost around $600.00 plus shipping both ways. He received them one day and shipped them back to us the next day, total turnaround time was six days. Since he deals with and recomends Wiseco pistons they will be clearenced properly. Just make sure they are broke in right and you warm up the engine properly befoe you crank on it hard. We've seen most problems with Wiseco pistons caused by people running a cold engine hard too soon.

  8. #8
    Quote Originally Posted by SilverFox23 View Post
    Standard bore is 69.75 mm. Wiseco has 5 oversize's, up to 72 mm. The piston kit comes with top end gaskets. My husband just had our youngest daughter's 750 engine bored by Bill Bune Enterprises in Anoka , Minnesota. If you buy the pistons from him and have him bore them it should cost around $600.00 plus shipping both ways. He received them one day and shipped them back to us the next day, total turnaround time was six days. Since he deals with and recomends Wiseco pistons they will be clearenced properly. Just make sure they are broke in right and you warm up the engine properly befoe you crank on it hard. We've seen most problems with Wiseco pistons caused by people running a cold engine hard too soon.
    I do that will all my vehicles.. let them warm up first... Especially my Hayabusa and my new supercharged sea doo. My Mag cylinder is the only questionable one.. I may opt to find a good used cylinder and stick with stock. I easily honed my #1 and #2. I honed my mag cylinder and it looks great but I've not mic'd it yet. I got a email from SBT they are telling me to jump .5mm requires a sleeve replacement. Booo well, its either replace a jug or go with SBT..thanks for the input. I'm sure I'll have more questions.

  9. #9
    Clayton G's Avatar
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    There is no way that you need to replace the sleeve if you bore it .5 mm. There are 4 more oversizes after .5 mm overbore. 72mm would be max and then you would have to resleeve. 72 on all 3 cylinders would give you 795cc's. I don't know what SBT is trying to do, look elsewhere.

  10. #10
    Quote Originally Posted by Clayton G View Post
    There is no way that you need to replace the sleeve if you bore it .5 mm. There are 4 more oversizes after .5 mm overbore. 72mm would be max and then you would have to resleeve. 72 on all 3 cylinders would give you 795cc's. I don't know what SBT is trying to do, look elsewhere.
    kind of what i thought..

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