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  1. #1

    2hrs on my 787 rebuilt 43cc miller head only 140 145 compression?

    Hello guys 2hours on my 98 spx 787 build. I know motors build compression as they break in but its been 2hours or 3hours on the tiny tach and front cylinder is 140 and rear is 145 compression with 43cc miller domes. Sbt pistons bore to 1.50mm oversize and .006 clearence, 6 hole base gasket and .55 squish both sides.

    Should I look for 39cc miller domes? what compression needs some mixing with race gas?


  2. #2

    Join Date
    Jul 2008
    Location
    Southeast Texas
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    101
    You should be @ 185ish#. Did you check the compression before you started the motor for a base line? 43cc domes are about the limit on pure (92/93) octane pump gas and .055" squish. I ran .043" and 185# (43cc domes) with no problems though.
    Pull the Raves and look at the piston skirts. You may have (unknowingly) "stuck" a piston.
    Robert V

  3. #3
    "Tearing it up on the water" seadoobutch787's Avatar
    Join Date
    Nov 2007
    Location
    Michigan
    Posts
    533
    I always did a 10hr break in and mixed oil with the fuel on oil injection.

  4. #4

    Join Date
    Jul 2008
    Location
    Southeast Texas
    Posts
    101
    Same Here. A+

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