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  1. #1
    VXSXH20's Avatar
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    Octane 777 cylinder head Question

    Got My Octane/777 torn down checked crank and bearings pulled domes...for whatever reason the cylinder heads are not dished like the stock oem style. They have more of a pointed taper cut to them. after the inspection, I got some stock heads and they are different. The tops all have same polaris ID stamping on them. just the dome is dished differently, Could this mean the the heads were recut? I want to put some higher compression in this motor and run 93 pump gas, I already have a 85mm bore and pistons. The manual states a uninstalled stock head/dome has 47.2cc, What is ideal to cut off or mill down? will it change cc size? I'd really appreciate any and all polaris input , Thanks Guys!
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  2. #2
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    That head looks an awful lot like the heads on my 1200 from SBT. Do you by chance have an SBT motor in your ski?


    This look familiar????

    http://www.greenhulk.net/forums/show...=1#post1810496

  3. #3
    VXSXH20's Avatar
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    Yes, I believe it is, I bought the ski from a buddy who sent his original engine to be rebuilt, Must have been a swap/core and he went with the SBT. I had heard that they change squish to make stock compression levels and maintain a " Reliable" engine status... So I have some stock domes to put back on, However the Bores are at 85mm now, Can I NOT Run these stock domes? Or do they need to be macined for the larger bore? -Ive been running 93 octane this whole time, I couldve saved that extra cash!!

    -What I would like is to have them machined/shaved to bump the compression even more. Much like a knock off performance dome from watcon or hotseat, Anyone on here you recommend that can do this and I can send which ever set of heads to do so? Thanks Bryan!!



    Quote Originally Posted by BryanP View Post
    That head looks an awful lot like the heads on my 1200 from SBT. Do you by chance have an SBT motor in your ski?


    This look familiar????

    http://www.greenhulk.net/forums/show...=1#post1810496

  4. #4
    VXSXH20's Avatar
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    ive read your thread above, and i see theres not alot of "GOOD" to say about SBT, I have known guys to purchase a engine from them only to sell their skis shortly there after... I belive mine is..However It IS WHAT IT IS. My warranty would have been up long ago anyway. so I have checked the bores and the bearings and crank. It is still in good shape. I just need to have the heads cut properly to handle the larger bore. Did you have yours done, if so who did you end up going with? Thanks in advance!! -Joe

  5. #5
    john zigler's Avatar
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    the head on the left in the pic HAS had the dome "re-shaped". it does look like a SBT job. they do this to lower compression, and make engines live longer. also, alot of times, they "deck" cyls on the top and bottom, and need to open the heads up to lower compression because of the decked cyls.

    if you are now going to a 85mm bore, you need to have your heads match the new larger bore. if you were at 85mm before, your heads "may" be cut to match already, and maybe THAT is what we are seeing. you need to measure to be sure.

    if it is a SBT motor, there will be a sticker, and number stamped on the front cyl.....

  6. #6
    VXSXH20's Avatar
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    I do see the stamp on the cylinder. How do I check if the cylinders are decked? Do you mean the Piston skirts are cut shorter? I have the 85mm bore, SBT Job. The pistons say 1.00 on the tops. Can I run a higher compression dome on these cylinders? Or just put my other set of OEMs that need to be opened up from 84 to the now 85mm?

  7. #7
    VXSXH20's Avatar
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    What is the max compression these 777s can handle on 93 octane?

  8. #8
    john zigler's Avatar
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    Quote Originally Posted by VXSXH20 View Post
    What is the max compression these 777s can handle on 93 octane?
    going by memory, i believe 150 to 160 range. the octanes are prone to detonation, so keep an eye on your piston crowns for signs of that.

    sorry, my bad, i was thinking 85mm is "big bore". that is only 1mm over stock, and no need to cut heads bigger. i was thinking 87mm

    you would ahve to measure the height of the cyls, and compare to stockers to see if they have been decked at all. it can be difficult to rebuild a SBT motor as they change things like this....

  9. #9
    VXSXH20's Avatar
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    only 1mm over stock, and no need to cut heads bigger

    I have heard that if 84mm stock domes are put on the 85mm piston bores that it will cause issues.. I will have to double check my compression levels now with the sbt heads. I should correct myself and say that cylinder jugs are still assembled. I really dont have any way to measure or see if the skirts or cylinder jugs have been machined. I want to just bump the compression on the engine slightly and have the CDI recurved as alot of the octane guys do.

  10. #10
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    Those heads you have from SBT are fine with the motor you have. I would be careful raising compression more on the SBT motor. It may not hold up too well. Maybe just recurve the CDI and run it how it is.

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