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  1. #1
    Prospect
    Join Date
    Nov 2016
    City
    midway
    State
    Utah
    Posts
    7

    Low cranking compression

    I have a 2012 SG with a 107 build which was set up with 10.5 to 1 compression ratio. When checking for cranking compression I only get 140 lbs on both cylinders. I have followed the SM instructions and disconnected the CR and have the throttle body wide open. The bike DYnos out at 112 hp and 118 lb torque and runs strong. Big Boyz compression calculators said it should make around 175 lbs with 585 cam at 5600 ft of elevation. What am I missing here. Tried both cold and hot with similar results.

    Mike T

  2. #2
    Administrator hulkss's Avatar
    Join Date
    Sep 2013
    City
    Luck
    State
    Wisconsin
    Posts
    610
    Hot engine is the correct way.

    Gauge in one cylinder and spark plug out from the other.
    Leave bike shut off.
    Block throttle body open (I use a screwdriver handle).
    Crank using a remote starter switch (bike shut off). That way no fuel is injected, ACR's will be closed for sure.
    Crank until gauge stops increasing. 5 seconds or so.
    2019 FLHCS

  3. #3
    Prospect
    Join Date
    Nov 2016
    City
    midway
    State
    Utah
    Posts
    7
    That's exactly how I did it only did not use remote starter switch but disabled the ACR.

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