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Leak Test Results after repair

Discussion in 'Mechanic and Repair' started by ed2hess, Feb 15, 2010.

  1. ed2hess

    ed2hess LawnSite Fanatic
    Messages: 14,460

    I just got a leak tester last week and started using it. Out of the four 15HP EV15T Kohler engines I measured, all were in the red zone. Significant leaks at the exhaust valve and rings. I have cleaned up the valves and that improved leak results(in yellow). Next I will be putting on the rings and scuffing(light hone) the cyclinder. After putting on the rings should I expect the leak results to be significanlty better immediately or will I have to run the engine in first?

    Don't know why I never invested in the $150 leak tester from ORiley.
  2. SMB

    SMB LawnSite Senior Member
    Messages: 323

    Someone correct me if I'm wrong, but I don't believe leak test results are accurate if the engine is cold. The clearances and sealing of the rings are different when cold than when hot. While the valves would most likely be the same whether hot or cold, I think you're looking at a lot of variation with the rings. You didn't mention the temps that you're using the leak tester so all I can do is guess but to answer your question...

    After re-ringing, the rings will have to seat themselves before you're up to full compression.
  3. Jay19LM

    Jay19LM LawnSite Member
    from Mo
    Messages: 31

    Don't know why I never invested in the $150 leak tester from ORiley.[/QUOTE]

    I was a tech for 12 years and a leak down tester will save you a lot of time. If you are working on a twin cyl. you can quickly diagnose which side is giving you problems. I used mine more for finding valve or head gasket problems. If the engine starts ok, has no loss of power, NO blowby, no smoke from exhaust and little oil consumption then I would dismiss your readings at first to being the rings or cylinder. Make sure you have the cylinder on tdc. If you are hearing air leak thru your dipstick tube it could be a head gasket or valves leaking. Also a push rod off or a broken rocker can fool you, the cylinder may show no leakdown, but it won't show you if the valve is opening or not. As in my case, the more you use the tool the more you will learn. Oh, hot or cold. I would check cold first. Valves should not leak regardless of temperature. A head gasket leak may seal up after heat expansion and if the rings or cylinder are that bad it probably won't start anyway. jay
  4. ed2hess

    ed2hess LawnSite Fanatic
    Messages: 14,460

    I am curious if the engine manufactures would cover an engine if it was leaking 50% near the end of warranty? I have limited experience with leak testing but I see units measuring up in the 80% range and are still starting and running okay. They burn a little oil.

    I was thinkking I would measure my 25hp on a Scag that is right at the end of warranty and has 1000 hrs on it.
  5. rotti1968

    rotti1968 LawnSite Member
    Messages: 169

    More then likely they would not unless there was a clear defect. most of the engines i leak down test and they fail are do to a: high hours and age, and b: lack of maintenance. The ones with lack of maintenance 9 times out of 10 have been dirt ingested and you can clearly see it . and as was said above the more you use the tool you will be able to pick out the issue right away.
  6. 2low4NH

    2low4NH LawnSite Bronze Member
    from NH
    Messages: 1,890

    wow i just bought one yesterday well compression anyway. my kohler command 15hp had an oil leak decided to fix that oil leak and decided hey why not check everything. found bad rings. it only smoked on little puff on start up. i pulled the head and found alot of play in the piston side to side movement and the plug was wet and black. the exhuast port was also gummed up with burnt oil. the sad part is the mower ran great besides the oil leak on the crank. im now shopping for rings and gaskets. i think the tester just helped me avoid a downed mower this summer
  7. ed2hess

    ed2hess LawnSite Fanatic
    Messages: 14,460

    You will definitely want to grind the valves. And I think I was told that the puff of smoke can be a bad valve seals(they are easy to replace). I got my first one I rebuilt back on the unit and it started so passed first test. Next I will get the second one the I did(did two at a time).
  8. 2low4NH

    2low4NH LawnSite Bronze Member
    from NH
    Messages: 1,890

    dont you need special tools to grind the valves
  9. GravelyNut

    GravelyNut LawnSite Bronze Member
    Messages: 1,594

    To grind them right, yes. And once ground, you need to lap them in. Lapping them in is the final step in getting the valve and seat to being as close a perfect match as possible.
  10. ed2hess

    ed2hess LawnSite Fanatic
    Messages: 14,460

    There probably is a better way than what I do but.....just put lap compound on them and use drill to turn the valve. You can put pressure on the valve to grind it against the seat. Seems to work.

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