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Thread: 1937 ULH low Cylinder Pressure

  1. #1
    Join Date
    Sep 2009
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    Alaska
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    Default 1937 ULH low Cylinder Pressure

    Ok guys, here we go again. I went and bought new cylinders from CycleFab, with fitted pistons and valves. I had my head surfaces checked on a friends CNC Mill, they were warped, it took .020" to get them flat. Put her together and it felt like no compression when I kicked her. I put a quality compression gauge and 22 PSI. I squirted a little Corrosion X in and 26 PSI.Double checked the valve clearances and perfect. Now, with milled heads and new cylinders with fitted pistons, my PSI should be up there a little more. Only answer would be a HUGE ring gap, or possibly the cylinder decks didn't get machined enough? She's on the lift begging to get tore down, but I may be missing the obvious????
    Steve

  2. #2
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    Sep 2009
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    Alaska
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    Default

    Oh, annealed copper head gaskets.
    Steve

  3. #3
    Join Date
    Aug 2004
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    Beautiful Northern New Mexico
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    3,074

    Default

    Throttle wide open for the test?
    Robbie Knight Amca #2736

  4. #4
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    Sep 2009
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    Alaska
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    Default

    Yes, wide open
    Steve

  5. #5
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    Aug 2004
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    Beautiful Northern New Mexico
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    3,074

    Default

    Clutch not slipping?
    Robbie Knight Amca #2736

  6. #6
    Join Date
    Oct 2011
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    580

    Default

    Any chance the cam timing is off?
    Tom

  7. #7
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    Jul 2017
    Location
    NW Ct.
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    107

    Default

    Rings on upside down? Valves seating properly?
    Last edited by HDSmitty; 03-12-2020 at 11:58 AM.

  8. #8
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    Sep 2009
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    Alaska
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    Default

    I'm checking all of that today, Thanks
    Steve

  9. #9
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    Sep 2009
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    Alaska
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    So I just heard that some of Cyclefabs ULH guides aren't concentric with the seats. Really? Holy Sh*t! I heard this guy was great. Ok, leak down test this weekend! Everything else checks out. Lifter clearances, clutch fully engaged. I took my OEM cylinders off after starting her because it was .060" over and the valve seats were so deep that I had to make special 7/16" wrenches to fit down in the lifter blocks to adjust them.
    Steve

  10. #10
    Join Date
    Nov 2008
    Location
    Virginia
    Posts
    538

    Default

    I would be careful here as Paul uses Kibbelwhite valves and guides for those. May not be a problem from him but them. He has them made up specifically for him and to his specs. so would think that if there is a problem it would be with all of them. I know several folks who have his cylinders and that was never a problem for them. Might have had other small issue but not that. I have had him do several motors for me over the years and while I can't recommend him right now due to delays in getting work out I would say he has spent more time and money figuring out HD flat head than anyone I know. I am sure if you find he is at fault he will make it right. Good luck!

    Tom (Rollo) Hardy
    AMCA #12766

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