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YICS and compression testing

Discussion in 'XJ Technical Chat' started by mack, Feb 19, 2014.

  1. mack

    mack New Member

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    Is it possible to accurately check the compression in each cylinder without the tool being installed?
     
    mack, Feb 19, 2014
    #1
  2. quebecois59

    quebecois59 Well-Known Member

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    I don't see any correlation between the YICS passage and compression in the cylinders, but do the test with YICS and then without and see if there is any difference. The important thing is to make sure the throttle is wide open.
     
    quebecois59, Feb 19, 2014
    #2
  3. bigfitz52

    bigfitz52 Well-Known Member Premium Member

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    YICS has no effect on compression test results. No need to block it.

    Just be sure your throttles are wide open, and unplug the TCI unit.
     
    bigfitz52, Feb 20, 2014
    #3
  4. mack

    mack New Member

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    carbs aren't on the bike so open throttle isn't a problem. My #3 cyclinder really struggled to achieve 118 psi. Had to roll the engine a long time to get to that. Twice as long as the others but it did have pressure. Could be dirty seat. I've reshimmed since as only one valve was in spec! No evidence of a head gasket leak. Now the shims are in spec I'll do another cold compression check and see if it's still struggling. If so the then it looks like the head will have to come off and the valve train inspected for broken springs or maybe a lapping on #3.
     
    mack, Feb 20, 2014
    #4

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