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  1. #1

    Compression test results?

    Guys

    I ran a compression test this morning to get a pre winterization health check.
    I could only run the test on a cold engine, but I'm more interested in the cylinder comparison numbers than absolute numbers.

    The first test I ran I only removed one plug at a time and saw 150-135-150. I then removed all three plugs and saw 140-115-140. Finally, I re-run the first test (only one plug out at a time) and saw 145-120-140.

    So, accepting that this was a cold engine test, how does this look? Should I be concerned? Or is the test on a cold engine a complete waste of time?

    Thoughts?


  2. #2
    twokexlv6coupe's Avatar
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    Ehh not a complete waste of time since it's telling you #2 is >10% difference, so it's something for you to be mindful of.
    You could've also done a cold wet test by pouring a capful of oil into each cylinder before testing, and if the compression increases "could" hint of piston rings being slightly worn out which would explain a lower number.

    Personally I'd be more worried if those were the results on a warm engine. Just curious as to why you couldn't do it on a warm engine? Even just 5 minutes I think is adequate enough to expand the piston rings enough.

  3. #3
    Eastside Powersports Slow 91's Avatar
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    pull the rockers off and leak down test it to see where the low compressions coming from. when you installed the stainless steel valves was the valve job done? or just hand lapped in the new valves?

  4. #4
    Quote Originally Posted by twokexlv6coupe View Post
    Ehh not a complete waste of time since it's telling you #2 is >10% difference, so it's something for you to be mindful of.
    You could've also done a cold wet test by pouring a capful of oil into each cylinder before testing, and if the compression increases "could" hint of piston rings being slightly worn out which would explain a lower number.

    Personally I'd be more worried if those were the results on a warm engine. Just curious as to why you couldn't do it on a warm engine? Even just 5 minutes I think is adequate enough to expand the piston rings enough.
    Will run cold wet test and see if it changes.

    Don't like running it on the hose for more than my usual 30 seconds flush. Those damn carbon seals love to cook and crack.

    Maybe I have to wait until next season and test after riding. Who knows, might just man up and brave the cold for a quick 5 min blast.

  5. #5
    Quote Originally Posted by Slow 91 View Post
    pull the rockers off and leak down test it to see where the low compressions coming from. when you installed the stainless steel valves was the valve job done? or just hand lapped in the new valves?
    I still have stock OEM original valves. I only upgraded the springs n retainers (Riva).

    As I don't have a leak down tool, could I move each cylinder to TDC in turn and pressurise with my Riva valve tool? Then I should be able to see / hear where the pressure releases, reasonable thought?

  6. #6
    No need to get the ski off the trailer. Just pull it into the water strapped to the trailer and warm the ski up. Do a compression test when you pull the warm ski up the ramp.

    Andy

  7. +1 by:

    JPR

  8. #7
    Quote Originally Posted by whittlebeast View Post
    No need to get the ski off the trailer. Just pull it into the water strapped to the trailer and warm the ski up. Do a compression test when you pull the warm ski up the ramp.

    Andy
    Will try, but all the ramps local to me have shitty, gritty, leaves and twigs just below the surface which I worry about sucking up (has happened twice to others I ride with, even when just running idle).

    I'll see if I can find a cleaner, longer ramp to use. Can also change oil before winter then too.

    Do you think the warm numbers will be closer and more even to each other? The engine has 120hrs and has only been mildly modded over the last 30hrs use.

  9. #8
    Eastside Powersports Slow 91's Avatar
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    Quote Originally Posted by tornado34 View Post
    Quote Originally Posted by Slow 91 View Post
    pull the rockers off and leak down test it to see where the low compressions coming from. when you installed the stainless steel valves was the valve job done? or just hand lapped in the new valves?
    I still have stock OEM original valves. I only upgraded the springs n retainers (Riva).

    As I don't have a leak down tool, could I move each cylinder to TDC in turn and pressurise with my Riva valve tool? Then I should be able to see / hear where the pressure releases, reasonable thought?

    my bad, wrong member.

    you can use the riva air line if you are able to regulate the air from the compressor. Put like 50psi or so into the cylinder and listen for the air leak. Pull the dipstick out as well.

  10. #9
    OK, so I'm gonna get out and run a warm engine test this weekend, but in the meantime I thought I'd try a wet cold test. Very interesting. The numbers rose to;

    180(was 145 so that's 24% improvement)
    210(was 120 so that's 75% improvement)
    165(was 140 so that's 18% improvement)

    So on this basis it looks as though it's a piston ring / cylinder wall leak? Strange because I use no oil and there is no exhaust smoke. It there any other reason that the wet oil test could increase the compression by such a high % (75)?

  11. #10
    Need to open up the throttle body when doing the test.

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