is small pin bored over better than stock SXR?
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  1. #1
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    is small pin bored over better than stock SXR?

    So I've been doing a tonne of reading through the threads and it seems to be a consensus that the 750 small pin has better low end than the big pin which is good for me cus I'm 260 pounds. That being said I bought a 750 small pin and put it in my sxr (motor grenaded). As of right now it is stock bore, will I need to rejet the SXR carbs? The sxr was running stock everything. if anything it should be rich right? so motor won't blow up if I try it out?
    I see that Wiseco makes a 5mm over 85mm small pin piston! that seems crazy, how much overbore can you do before the cylinders are too thin?

    http://www.ebay.ca/itm/Wiseco-WK1091...5ZKWUc&vxp=mtr


    I'm thinking a 750 small pin with 85mm pistons would be a beast! Anyone do this or know of any success doing this?

    Cheers

  2. #2
    Top Dog bandit88's Avatar
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    Re: is small pin bored over better than stock SXR?

    SXR Cases are better than SP cases, the SP cylinder will have slightly better bottom and slightly worse top than a SXR cylinder. You can go up to 2mm over on a SP cylinder and anything over that will require larger sleeves. Do not bore to the max 2mm over, you will not get any noticeable performance increase and will just be wasting that cylinder. You will need to rejet the carbs as the porting is different, but you should be close with the stock settings, then tune from there. You will probably need to bring the pilot down a size or two. If I were you, I would fix the SXR motor and run that.
    -95 750SXI
    -86 440 with PJS800 conversion - http://www.pwctoday.com/showthread.php?t=466927
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  3. #3
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    Re: is small pin bored over better than stock SXR?

    Quote Originally Posted by bandit88 View Post
    SXR Cases are better than SP cases, the SP cylinder will have slightly better bottom and slightly worse top than a SXR cylinder. You can go up to 2mm over on a SP cylinder and anything over that will require larger sleeves. Do not bore to the max 2mm over, you will not get any noticeable performance increase and will just be wasting that cylinder. You will need to rejet the carbs as the porting is different, but you should be close with the stock settings, then tune from there. You will probably need to bring the pilot down a size or two. If I were you, I would fix the SXR motor and run that.
    Thanks for the reply. Ok the resleeve makes sense, I didn't think you could bore that much over.
    I'd happily rebuild the sxr motor if possible. A rod busted and blew out the side, taking out one of the sleeve at the bottom/skirt, starter motor, and the cases are totally blown up and I don't have all the pieces as I bought it blown up. After pricing out new cases, resleeve and bore, pistons, rebuilt crankshaft (it a hundred bucks each way for shipping to Canada alone) etc its more than I can afford right now so I just picked up a used small pin and I'll see what I can do with that.
    Cheers

  4. #4
    PWCToday.com Is My Home Away From Home mcn6's Avatar
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    Re: is small pin bored over better than stock SXR?

    SP #22 casting cylinder has almost identical port durations to an SXR cylinder. SP #20 cylinders exh. port is 3mm lower than a #22 cylinder. Both SP cylinders need to have their lower sleeves clearanced for use with BP bottom ends. If you don't want to clearance the sleeves you could run a BP cylinder, but bottom end will suffer compared to an SXR cylinder.

    Max bore size varies a little from cylinder to cylinder for both SP and BP. But, you cannot get anything near 85mm bore diameters from OE SP or BP cylinders.



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  5. #5
    Top Dog bandit88's Avatar
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    Re: is small pin bored over better than stock SXR?

    Yep, not worth fixing when a rod lets go.
    -95 750SXI
    -86 440 with PJS800 conversion - http://www.pwctoday.com/showthread.php?t=466927
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  6. #6
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    Re: is small pin bored over better than stock SXR?

    Quote Originally Posted by mcn6 View Post
    SP #22 casting cylinder has almost identical port durations to an SXR cylinder. SP #20 cylinders exh. port is 3mm lower than a #22 cylinder. Both SP cylinders need to have their lower sleeves clearanced for use with BP bottom ends. If you don't want to clearance the sleeves you could run a BP cylinder, but bottom end will suffer compared to an SXR cylinder.

    Max bore size varies a little from cylinder to cylinder for both SP and BP. But, you cannot get anything near 85mm bore diameters from OE SP or BP cylinders.
    Mcn6 If you put a SP cylinder on a BP bottom end, do the BP pistons need to be cut? Donít SP pistons have a little cutout near the bottom of the skirt?


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  7. #7

    Re: is small pin bored over better than stock SXR?

    Great question^

  8. #8
    PWCToday.com Is My Home Away From Home mcn6's Avatar
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    Re: is small pin bored over better than stock SXR?

    Install them and go, you don't need to do anything to the pistons.

    Quote Originally Posted by namart1 View Post
    Mcn6 If you put a SP cylinder on a BP bottom end, do the BP pistons need to be cut? Don’t SP pistons have a little cutout near the bottom of the skirt?


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  9. #9
    PWCToday.com Is My Home Away From Home Bruce in SB's Avatar
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    Re: is small pin bored over better than stock SXR?

    Have Newmiller port that small pin for low end and you will be amazed
    "Thanks" to Chris Newmiller @ Newmiller Machine

  10. #10
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    Re: is small pin bored over better than stock SXR?

    Quote Originally Posted by Bruce in SB View Post
    Have Newmiller port that small pin for low end and you will be amazed
    I would for sure if I had any money (shipping from Canada would kill me)....heard nothing but good things about Chris Newmiller! thanks for the input guys

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