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  1. #1
    Jkmike's Avatar
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    Oversize pistons... Which ones are best?

    Hey yaw,

    Getting ready for my winter build on my way RXT-X 260. I will be converting over to the 300 XXX Charge and building the bottom end of the motor. I have already ordered a set of Molnar rods, now I just need to decide on pistons.

    Right not I'm trying to decide between the CP 9.5 100.25mm and Eastside 9.5 100.5mm pistons. Anyone have any thoughts on which are better?

    My biggest concern with the Eastside pistons are the smallest oversize piston Chris makes is 100.5mm, and I'm just wondering if having to bore out the sleeves that extra 0.25mm (0.01in) could cause any potential strength issues?


  2. #2
    ptscon's Avatar
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    I've used .5mm oversize no issues, the nice thing about .25 is you always have .5 to fall back on if you need to redo it in the future. There are 101mm pistons as well.

  3. #3

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    I have never used the eastside pistons but being he is the legend for these 4tecs I wouldnt hesitate to use them. I personally use the cps and have no issues.

  4. #4
    Eastside Powersports Slow 91's Avatar
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    Quote Originally Posted by Jkmike View Post
    Hey yaw,

    Getting ready for my winter build on my way RXT-X 260. I will be converting over to the 300 XXX Charge and building the bottom end of the motor. I have already ordered a set of Molnar rods, now I just need to decide on pistons.

    Right not I'm trying to decide between the CP 9.5 100.25mm and Eastside 9.5 100.5mm pistons. Anyone have any thoughts on which are better?

    My biggest concern with the Eastside pistons are the smallest oversize piston Chris makes is 100.5mm, and I'm just wondering if having to bore out the sleeves that extra 0.25mm (0.01in) could cause any potential strength issues?
    Hello, just to clarify, my pistons come in any size you need. However, my premium ring set is not available in 100.25mm, CP pistons as well have a different ring set for their 100.25mm pistons.

    As for CP pistons, I was a huge fan of them for many years, until about end of last year when I was seeing a lot of guys blowing half the piston apart, and they were all failing in the same area on the skirt. I did speak with CP on this several times and they did say they changed their alloy/design/etc, but they would not offer any type of compensation so I ended up teaming up with Diamond Pistons who currently make ALL my custom pistons For 260/300/ Yamaha SVHO and more.

    As for strength issues, I have run up to .40" with zero issues.

  5. #5
    marcroberts's Avatar
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    Quote Originally Posted by Jkmike View Post
    Hey yaw,

    Getting ready for my winter build on my way RXT-X 260. I will be converting over to the 300 XXX Charge and building the bottom end of the motor. I have already ordered a set of Molnar rods, now I just need to decide on pistons.

    Right not I'm trying to decide between the CP 9.5 100.25mm and Eastside 9.5 100.5mm pistons. Anyone have any thoughts on which are better?

    My biggest concern with the Eastside pistons are the smallest oversize piston Chris makes is 100.5mm, and I'm just wondering if having to bore out the sleeves that extra 0.25mm (0.01in) could cause any potential strength issues?
    I can say I have had 2 complete sets.from chris one standard bore one set oversize absolutely best bang for the buck. Motor I race now has over 20 motos and zero issues and I twist my motors around 9200 rpm range.

  6. #6
    Jkmike's Avatar
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    Thats awesome to hear. I have been talking with Chris a bunch. I'm more than likely gna go that route.

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