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  1. #1

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    werid compression problem

    Hi,
    long story short. I got a 96 Polaris SL 780. the front two cylinder is bad. the compression is
    1. 0
    2. 50
    3. 125

    so i went on line and get two cylinder with 2 new pistons. install it. now the reading is
    1. new 125
    2. new 125
    3. drop from 125 to 90

    why????
    can i run the jet like this? please input.......


  2. #2
    Tony's Avatar
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    Are you using the same gauge? Put a 1/2 teaspoon of 2 stroke oil in the cylinder and see if the compression comes up.

  3. #3

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    Quote Originally Posted by Tony View Post
    Are you using the same gauge? Put a 1/2 teaspoon of 2 stroke oil in the cylinder and see if the compression comes up.
    I use some fogging oil to do the test, I will tey the 2 stroke oil. and post thanks.

  4. #4
    bowsniper's Avatar
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    they say no more than 5% between cylinders. some go 10%. yours is over 20%. how many times did you check that last cylinder? just once? maybe try it again and see what you get.. make sure the other 2 have the plugs out and your wot when cranking..

  5. #5
    Canadian Beaver Inspector jkindt's Avatar
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    Make sure your battery is FULLY charged and spinning that motor at full speed, your plugs are ALL out, and you hold the throttle wide open when testing.

  6. #6

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    Quote Originally Posted by bowsniper View Post
    they say no more than 5% between cylinders. some go 10%. yours is over 20%. how many times did you check that last cylinder? just once? maybe try it again and see what you get.. make sure the other 2 have the plugs out and your wot when cranking..
    I test it with the other 2 plug off, since I am rebuilting the whole thing the engine is still sitting outside with no hook up beside the starter for testing. What to make sure everything work before i put eventhing back in the hull. I tested 4 times. the compress when from 50 to 90 during the 2nd test, but remain 90 on 3-4 test.

  7. #7

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    OMG...... after putting in the oil and do the compression test. the 3 rd cylinder jump up to 110....... BUT
    here is the new reading....

    1) 150
    2) 150
    3) 110


    What should i do?

  8. #8
    bowsniper's Avatar
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    maybe a ring is sticking on that piston. it will run like that but not sure if thats a great idea though.. maybe some new rings and a quick hone on no. 3. those 150's are high because of the oil in there. normally the ski doesnt have that much oil in the cylinder. wait for exlint to reply and see what he thinks about the situation..

  9. #9

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    the problem is that it was 125 before......

    I swap the cylinder to different location, still no help.
    here is what i notice.
    1) this happened after i clean the carbon builtup at the top. This should not affect any thing....
    2) the piston rings look shorter to me. the other 2 piston's rings close up pretty good. but this piston with problem have a small gap where the ring meet.... it wasn't broken it just become "shorter" but it is not a big gap thought.....

  10. #10
    seaobin's Avatar
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    Im with bow, get new rings, quick hone and reinstall. cost you $25 for rings. you then know you are ok

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