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  1. #1
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    Smile Compression Test Results with JSRE Heads

    Completed the compression test on my 2005 Mercury XR6 150. Heads were shaved by JSRE. These are O-ring heads. I followed the procedure listed in the FAQ with the exception of having the throttle plate closed vs open. I'm unsure what, if any, effect that had on results.

    Numbers are 130, 143, 140, 135, 135, and 138.

    I didn't test for any specific reason other than I was curious.

    That is all.
    2004 Tracker Avalanche with 150 Mercury XR6

  2. Member 123trentm's Avatar
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    #2
    130-143 variance is on the verge of rebuild/re-ring

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    #3
    More than 3 lb variance within each bank is a red flag for me. Tome to re-ring. (Sometimes there is a difference on each bank)

  4. Member 123trentm's Avatar
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    #4
    Is it possible the low cylinder isn't sealing properly since being shaved? I've never used a shaved o-ring head. Just curious

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    #5
    Run it!

  6. Member lpugh's Avatar
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    #6
    I would have performed a proper compression and leak down before any mods were done!

    I would not run it until I new why it has that much variation, Re check the compression with the motor warmed up, throttle wide open and a battery charger hooked up to be sure the voltage does not drop causing reduced rpm on the latter cylinders being checked.
    Should do a camera or bore scope inspection of the cylinder walls and piston tops at the same time

    5 psi bank to bank is fairly common and does not indicate a problem, 10 % hole to hole on the same bank is indicating something has changed in a negative way, industry wide it is considered expectable. Not in my eyes though..... 5 % compression variation and 5 % leak down max
    I am a strong advocate of taking care of little things to prevent the unplanned major problems


    Then leak down test at least on the lower compression holes at tdc and part way down, just be sure the rings are above the ports
    This test should be done by an experienced tech as there are some dangers involved, proper safety measures must be taken
    Last edited by lpugh; 09-17-2019 at 06:56 PM.
    Thank You Leon Pugh

  7. Member silverbullet02's Avatar
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    #7
    Go run the snot out of it then try again. That’s not far out enough to worry about. Sometimes a good run will even them out, especially if it sat for a little bit. Even at that, the rule of thumb has generally been 10% difference.
    1995 Allison XB-2003 225 Super Mag. It's slow and I'm ok with that.

  8. Member lpugh's Avatar
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    #8
    I would not bet the price of a powerhead on that, I would find out why before making that statement
    Thank You Leon Pugh

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    #9
    Quote Originally Posted by silverbullet02 View Post
    Go run the snot out of it then try again. That’s not far out enough to worry about. Sometimes a good run will even them out, especially if it sat for a little bit. Even at that, the rule of thumb has generally been 10% difference.
    130 & 143 is 10% difference. A good motor with cut heads runs with a lot more snap to it, but it will also ruin a worn motor a lot quicker.

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    #10
    I retested this morning prior to doing a decarb. I let the engine warm till the thermostat opened plus an additionl 10 minutes. I opened the throttle this time (tied the butterfly valve linkage open) and turned the motor 4 times to a "3" count on each cylinder.

    Per Leon's advice I also hooked up a charger set at 40amps.

    Pre decarb 145, 156, 151, 148, 148, 149
    Post decarb 146, 153, 150, 149, 149, 149

    The readings are somewhat subjective as my pressure gauge is graduated in 5psi increments from 50psi - 300psi
    2004 Tracker Avalanche with 150 Mercury XR6

  11. Member lpugh's Avatar
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    #11
    Good job, that would put my mind at ease. With those numbers a leak down would not be in order.

    That is really high numbers for a two stroke. If the gauge is accurate, I would be concerned with that much compression on a fishing motor. You will need the highest octane fuel you can get. Don't fret over the fuel containing alcohol as it can actually run a little cooler
    Might be wise to reduce the WOT timing a couple of degrees and be sure the fuel system is in perfect condition
    Maybe Don, Savage or Joe can add more to this, those numbers would roughly represent about a 9 to 1 compression ratio
    Might be a good idea to rig a regulated air supply to the tester to verify how accurate it is. To do this, air must flow thru the Schrader valve to be valid
    Last edited by lpugh; 09-18-2019 at 10:37 PM.
    Thank You Leon Pugh

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    #12
    Quote Originally Posted by lpugh View Post
    Good job, that would put my mind at ease. With those numbers a leak down would not be in order.

    That is really high numbers for a two stroke. If the gauge is accurate, I would be concerned with that much compression on a fishing motor. You will need the highest octane fuel you can get. Don't fret over the fuel containing alcohol as it can actually run a little cooler
    Might be wise to reduce the WOT timing a couple of degrees and be sure the fuel system is in perfect condition
    Maybe Don, Savage or Joe can add more to this, those numbers would roughly represent about a 9 to 1 compression ratio
    Might be a good idea to rig a regulated air supply to the tester to verify how accurate it is. To do this, air must flow thru the Schrader valve to be valid
    Much higher than 9.0 to one compression. Actual at port timing over 10:1. 14.7 lbs for each ratio. Theoretical ratio over 12:1 but you lose roughly 20% of the charge before the exhaust port is closed. The motor being aluminum can handle higher ratios than if it had iron heads.

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    #13
    bumping 150 all around is a bunch for a fishing mtr , you need to be vey careful about fuel and cooling system maintenance also, personally on an Avalanche if its still on it I wouldnt do that , just too heavy a rig to benefit from mods other than reeds for safety factor, just my opinion
    .................................................. ...the scariest thing in life is the unknown ...................................

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    #14
    Thanks for the advice. Jay had said I could continue to run 87. He didn't cut the heads himself however. When he received them and discovered they were O-ring heads he forwarded them to his shop in NC to be cut. I'll begin to run 93
    2004 Tracker Avalanche with 150 Mercury XR6

  15. Member silverbullet02's Avatar
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    #15
    Yeah, you don’t wanna run 87 in that. Should run good though.
    1995 Allison XB-2003 225 Super Mag. It's slow and I'm ok with that.

  16. Member 123trentm's Avatar
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    #16
    That's better numbers!! What spark plugs are you running? Read your plugs. Might have to rejet carbs. Definitely check timing. I wouldn't go over 23 degs, unless you index and find most advanced cylinder.

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    #17
    Quote Originally Posted by 123trentm View Post
    That's better numbers!! What spark plugs are you running? Read your plugs. Might have to rejet carbs. Definitely check timing. I wouldn't go over 23 degs, unless you index and find most advanced cylinder.
    I'm certainly no expert reading plugs but I thought they looked healthy. The ground electrode was dark and the tip was a light brown all the way around. 1/2 the plug was a little lighter than the other on each. I'm running the OEM plugs

    I'm inclined to leave timing as it is. I was under the impression the later production XR6s aren't easily changed due to their ignition system. If I was wrong I'd consider it.

    Jay's advice was to shaved the heads, run a Bob's tuner and call it good. He said the newer XR6s don't lend themselves to hot-rodding for multiple reasons
    2004 Tracker Avalanche with 150 Mercury XR6

  18. Member 123trentm's Avatar
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    #18
    I forgot it was CDM ignition. Yep, not much you can do.

  19. Member lpugh's Avatar
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    #19
    Crank sensor can be relocated to make timing adjustable, changing up to about 3 degrees is very simple, though this task should be preformed bay an experienced engine tuner, same thing goes for reading the plugs and inspecting the piston tops.
    Some above mentioned checking timing on every cylinder with this much compression and that would be wise, again requiring a
    experienced engine tuner to establish TDC marks for ever cylinder
    I would highly recommend against what you are attempting to do for a fishing motor unless you have deep pockets
    Thank You Leon Pugh

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    #20
    Ran 150 compression on all my fishing motors for over 20 years. Just run premium and you will be fine. Don';t need to do anything else. Enjoy your new pop!!

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