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  1. #1
    richrxp's Avatar
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    CP pistons 8.4:1 + 0.25mm,what size do i need to hone the cylinder?

    Is it as easy as just hone the cylinder to + 0.25 mm oversize and you are done?
    Is a 400 grit finish the way to go?
    I know the piston to wall clearance is important,but i just want some extra info,before i get my cylinders honed.
    Cylinders look just fine after 136 hrs,but due to a engine failure my engine is apart right now,and rehoning the cylinder and go first oversize seems the way to go.
    Was thinking just putting new rings in the stock pistons but i'm running 3Rude at around 8600- 8700 rpm,the cp are the way to go i think.


  2. #2
    formerly Gold06RXP Turbo Nick's Avatar
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    Just go with the clearence specified in the instructions

  3. #3
    i hate my bipolar disorder its great
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    you wont be able to hone your bores to the correct oversize youll be there for ever. a cylinder hone is just to clean the bores up and give the new rings something to bed into

    you want the block to be bored to suit the oversize of the pistons and then finished with a hone.

  4. #4
    big john's Avatar
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    at .25mm, most machine shops will hone the material out with a 180 stone, then finish up with a 240, 380 or 400, depends on what you tell him what the manufacture says, i would ask for a plateau finish hone if it was my motor, better ring break in and long term wear and tear IMO

  5. #5
    richrxp's Avatar
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    Ok thanks for all the help guys.
    I'wont be honing myself,i will go to the machineshop for this.
    Cp pistons first oversize is +0.25 ,this isn't something you can do yourself.
    I will order oversize pistons,my idea was to bring the cylinders to the machineshop to be honed,when the pistons arrive i can install them at once.
    Maybe i better first wait until the pistons arrive,and go with pistons and engine to the machineshop and have it honed,so they will be able to measure the clearance between piston and wall.
    It's my first total rebuild,done the head and valves before,but this is a new one for me.

  6. #6
    big john's Avatar
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    Quote Originally Posted by richrxp View Post
    Ok thanks for all the help guys.
    I'wont be honing myself,i will go to the machineshop for this.
    Cp pistons first oversize is +0.25 ,this isn't something you can do yourself.
    I will order oversize pistons,my idea was to bring the cylinders to the machineshop to be honed,when the pistons arrive i can install them at once.
    Maybe i better first wait until the pistons arrive,and go with pistons and engine to the machineshop and have it honed,so they will be able to measure the clearance between piston and wall.
    It's my first total rebuild,done the head and valves before,but this is a new one for me.
    they need the pistons to measure and get the piston to cylinder clearance right, CP makes a great piston, i run them in my harley 113 motor

  7. #7
    richrxp's Avatar
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    Thanks ,i will first order the pistons and then go to the machine shop.
    I was thinking of taking the cp pistons in stock size,because after 136 hrs,my stock pistons look like new,and the cylinder walls are fine also.
    Maybe stock size and a very slight hone would do the job also,that's the only thing i'm doubting about.

  8. #8
    suck my wake's Avatar
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    With the stock size replacement piston you can mostlikely hone and install, with an oversize you will need to have the cylinders bored first!!!!!

  9. #9
    richrxp's Avatar
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    Quote Originally Posted by suck my wake View Post
    With the stock size replacement piston you can mostlikely hone and install, with an oversize you will need to have the cylinders bored first!!!!!
    I will first meausure the size of the cylinders,if they are within spec,i will give them a hone and go with stock size.

  10. #10
    ROTAX RACING performance
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    the CP needs more clearance then stock pistons , + the CPs are slightly bigger compared to stock , measure the pistons and go for 0.075- 0.08 mm clearance

    you can hone a stock bore if you go with stock seize CP

    if you go with .25 over seize you need new bore, then hone, then polishing

    check ring clearance as well after the bore is rrady

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