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Thread: Piston wash

  1. #1
    cheatin' piston popper addicted's Avatar
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    Piston wash

    I've been reading up on this and am hoping that one of you experts could post some pictures and techniques for reading piston wash on PWC engines. Just about everything I found is snowmobile related, and apparently they can run much closer to the edge.

    A few specific questions. . .

    How long does it take to develop?

    Should you check the wash for the different carb circuts?

    What effect does your oil ratio and type have?

    Is it like doing a plug chop, or do you just ride around and then have a look?

    How many times can the head gasket be re-used?


    Thanks!


  2. #2
    Moderator RX951's Avatar
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    How to Read Pistonwash

    Here are some good links.....

    http://www.bikemanperformance.com/tech_detail.php?ta=4

    http://www.snowtechmagazine.com/arti...e/baseline.php


    This will give you some good general info about how to read your piston wash to accurately determine if you sled is running rich or lean. This is all based off a flat top style piston and a domed style piston may vary from these photos. These are general guidelines and dont take every factor/condition into consideration so dont call up bitching if you take these guidelines as law!!
    Pic of a Lean Piston
    The first piston is Lean. You can see it is almost completely black across the top of the piston. This is from the superheated gasses being immediatley carbonized onto the crown of the piston. This piston obviously seized and has alumium along the outer edge of the piston crown. Note: this is bad, you dont want this!
    Pic of a Rich Piston
    The second piston is Rich. You can see there is a very large amount of clean piston showing from all the transfer port areas on top of the piston. This is from the cool overly rich air/fuel mixture washing the top of the piston clean. Note: this is when you sled runs like crap. Ideally, you should have about a fingernail size portion of clean piston around each transfer port as shown in the next picture.
    Pic of a Normal Piston
    The last piston is just about right. This has a small portion of cleaned off portion at each transer port. Its a little hard to see clearly in the photo but a fingernail size portion is about right. This piston looks great for drag racing or even trail riding. A little more wash would be even a little safer.

    Pic of a lean piston


    pic of a rich piston



    pic of a richer piston





  3. #3
    Moderator RX951's Avatar
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    PERFECT BROWN Two-Stroke CROWN
    http://www.eric-gorr.com/tech/pistonguide.html

    The crown of this piston shows an ideal carbon pattern. The transfer ports of this two-stroke engine are flowing equally and the color of the carbon pattern is chocolate brown. That indicates that this engine's carb is jetted correctly.



  4. #4
    mtrager's Avatar
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    Great info,

    How does race fuel effect piston wash ?

  5. #5
    cheatin' piston popper addicted's Avatar
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    Wow! Great stuff. So if I understand this correctly, piston wash is an accurate way of determining if the total jetting is correct?

  6. #6
    Moderator RX951's Avatar
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    http://www.snowtechmagazine.com/arti...-t/dec2005.php

    Piston Wash – How Much?
    2-stroke engine tuners know that observing the amount of piston wash on the piston dome is a very accurate indicator as to the best fuel-air mixture for maximum power production in competitive situations. These small “clean areas” on top of the pistons, located where the fuel enters the combustion chamber at the transfer ports, are indicative of the amount of excess fuel entering the engine. The smaller the “wash”, the leaner the fuel-air mixture.

    How much is the perfect piston wash? The engine builders at Black Magic Racing tell us we should keep two important items in mind when we are looking at the wash on top of the pistons. Based on their experience (with Suzuki engines) the engines with flat top pistons can run less wash and not lose performance or detonate. The domed pistons need to run more wash than a flat top piston in order for the engine to run at peak performance.

    Flat top piston wash, at peak performance, will be the size of the nail on your little finger. You can get slightly smaller than this, but then the performance will begin to go down hill and the detonation point gets closer.

    Domed style pistons need to have a wash the size of the nail on your thumb or slightly less. The reason some of these engines just lose power and sometimes not even detonate, is due to the timing curve which is much milder on more stock motors .

    Remember, the amount of piston wash explained here is based on regular octane fuel. Running race fuel,if you have the compression to burn it, will allow the size of the wash to become less through jetting and not lose as much HP. If you are into getting the most out of your engines, use this rule of thumb to keep enough fuel thrown at it and avoid the burndowns.


    Common tuning tools when using higher octane & examining pistonwash during tuning.
    Digital Tach
    Boroscope
    EGT's
    Air/Fuel Analyzer
    Laser/Infrared temp surface thermometer
    Or physically pulling the head for a good visual inspection.

  7. #7
    cheatin' piston popper addicted's Avatar
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    My printer is now out of ink! I guess i'm not getting any "work" done today.

    Great info.

  8. #8
    Moderator RX951's Avatar
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    Hydrotoys Stock 1200 GPR Pistonwash.








    I just took pics of mine late last year...I'll post tonight when I get home.

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  9. #9
    Flying Scotsman's Avatar
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    Not bad I needed a refresher in wash

    #1 not bad
    #2 has less carbon looks good
    #3 has to much wash I think.(rich)

    I think #2 is your target what do you think.

  10. #10
    Moderator RX951's Avatar
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    Here's one I lean seized back in 04

    #3 piston




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