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Thread: ATC 90 and the 56mm piston won't work. What can I do to solve the problem?

  1. #1
    Join Date
    Mar 2010
    Location
    Wisconsin
    --
    201

    ATC 90 and the 56mm piston won't work. What can I do to solve the problem?

    So I asked questions and did some research and ppl said that the 56mm piston kit will work on the ATC 90. I had to get a 110 cylinder, crank/rod, head bolts and timing chain. I brought the cylinder to the machine shop and they said the wall will be paper thin. So after I have all the parts now I can't do it. The 54mm piston on DrATV is probably a 14mm wrist pin. Will a cylinder off a 125m swap over to my engine? Would this solve the problem?
    1978 ATC 90
    22mm Keihin carb
    Ported intake/head
    Performance cam
    56mm 9.5:1 piston
    110 cylinder/crank
    110 cylinder/ timing chain
    Front drum brakes
    Brush guard
    Complete rebuild to a 122cc
    Complete frame off restoration.
    $1400 invested

    1983 ATC 110
    22mm carb
    Ported head/intake
    Performance cam
    56mm 9.5:1 piston
    Complete rebuild to 122cc
    Complete frame off restoration
    $1000 invested

    1984 200x
    26 mm carb.
    CR85 rear caliper
    TRX hubs/rims
    $871 invested

  2. #2
    Join Date
    Jun 2005
    Location
    Jackson MI
    --
    1,688
    I think you will need to sleeve the cylinder up, and then bore the case's to fit the bigger sleeve.

    83 ATC 60-R Cr60 converted with Zinger parts.
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    83 Tri zinger
    ATC 85-R Cr85 engine on shortened 86-R frame.
    ATC450AF
    86 310-R Drag racer
    440 snowmobile powered custom built.
    87 Cr 500 Converted to Drag racer

  3. #3
    Join Date
    Nov 2007
    Location
    ulysses pa
    --
    1,231
    your STOCK ATC 110 cylinder will BORE OUT to use the 56mm piston. whats left of the sleeve is not actually paper thin and any one telling you this is full of crap. i have this exact set up sitting in my shed. im going to go measure whats left of the sleeve right now for you.

  4. #4
    Join Date
    Mar 2010
    Location
    Wisconsin
    --
    201
    Much appreicated. I think I will be taking it to a different machine shop.
    1978 ATC 90
    22mm Keihin carb
    Ported intake/head
    Performance cam
    56mm 9.5:1 piston
    110 cylinder/crank
    110 cylinder/ timing chain
    Front drum brakes
    Brush guard
    Complete rebuild to a 122cc
    Complete frame off restoration.
    $1400 invested

    1983 ATC 110
    22mm carb
    Ported head/intake
    Performance cam
    56mm 9.5:1 piston
    Complete rebuild to 122cc
    Complete frame off restoration
    $1000 invested

    1984 200x
    26 mm carb.
    CR85 rear caliper
    TRX hubs/rims
    $871 invested

  5. #5
    Join Date
    Nov 2007
    Location
    ulysses pa
    --
    1,231
    sorry i forgot this. you will be left with 1mm of skirt left all the way around the piston. doesnt sound paper thin to me, how about you? i think you have the right idea with going to a different machinest.

  6. #6
    Join Date
    May 2007
    Location
    Orange County, NY !
    --
    1,672
    Blog Entries
    2

  7. #7
    Join Date
    Nov 2007
    Location
    ulysses pa
    --
    1,231
    Quote Originally Posted by riverrat View Post
    How many cc's will this give you?
    should be 123 to 125cc.

  8. #8
    Join Date
    Mar 2010
    Location
    Wisconsin
    --
    201
    I came up with 122cc's. Their is a chart on DrATV.com.
    1978 ATC 90
    22mm Keihin carb
    Ported intake/head
    Performance cam
    56mm 9.5:1 piston
    110 cylinder/crank
    110 cylinder/ timing chain
    Front drum brakes
    Brush guard
    Complete rebuild to a 122cc
    Complete frame off restoration.
    $1400 invested

    1983 ATC 110
    22mm carb
    Ported head/intake
    Performance cam
    56mm 9.5:1 piston
    Complete rebuild to 122cc
    Complete frame off restoration
    $1000 invested

    1984 200x
    26 mm carb.
    CR85 rear caliper
    TRX hubs/rims
    $871 invested

  9. #9
    Join Date
    Mar 2010
    Location
    Wisconsin
    --
    201
    Monday I'm calling them and asking them again what the wall thickness will be. They measured the piston at 55.9mm. My micrometer gave me 55.5. It is advertised as a 56mm piston. They didn't give me any other measurements. If they won't do it I'll take it to a different shop. They are a bit more for the same service but at least I have another option.
    If I have to I will get it sleeved. I'd rather do that then not utilize all the parts I have collected.
    1978 ATC 90
    22mm Keihin carb
    Ported intake/head
    Performance cam
    56mm 9.5:1 piston
    110 cylinder/crank
    110 cylinder/ timing chain
    Front drum brakes
    Brush guard
    Complete rebuild to a 122cc
    Complete frame off restoration.
    $1400 invested

    1983 ATC 110
    22mm carb
    Ported head/intake
    Performance cam
    56mm 9.5:1 piston
    Complete rebuild to 122cc
    Complete frame off restoration
    $1000 invested

    1984 200x
    26 mm carb.
    CR85 rear caliper
    TRX hubs/rims
    $871 invested

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