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Help GJ73A compression & leak down test

Discussion in 'Suzuki 250cc In-line 4's' started by Damian Habib, Aug 7, 2021.

  1. Damian Habib

    Damian Habib Active Member

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    Hi guys,

    I have done some checking on a second hand engine I brought for my bike. I am not sure if what I have found is bad or not as I’m struggling to find info. I know some of the intake valves are right on the tight end of the tolerance. But should I be seeing more compression? I was surprised when I did the leak down test at how little it was leaking & it sounded like it was all past the rings.

    All the testing was done on a cold motor.

    IMG_6338.jpg


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  2. Linkin

    Linkin The Mechanic Premium Member Contributing Member Dirty Wheel Club

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    The rings are probably very tired given the age and revving inclination of these engines. That said, 10% leakage across all cylinders is acceptable. 20% or more becomes an issue.

    I would set all the clearances to maximum and re-test compression and leakdown. If there is no improvement, then it does need rings.

    EDIT: If you end up doing the rings I would also test the valves for leakage with the head removed. It's simple, you just pour petrol in the ports and check for leakage past the valves.
     
  3. risky

    risky risky

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    do 2 compression tests- first dry which you have and then with some oil in each cylinder. if the compression rises greatly then new rings minimum. if not valves may need lapping.
     
  4. Damian Habib

    Damian Habib Active Member

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    Thanks I’ll try a wet compression test tomorrow. Any idea how much oil to use ?

    Cheers


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  5. Linkin

    Linkin The Mechanic Premium Member Contributing Member Dirty Wheel Club

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    A small amount from a syringe will do - too much will affect the volume of the cylinder and give a false high compression reading
     
  6. risky

    risky risky

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    correct-try half a teaspoon or less.
     

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