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  1. #1
    Haven't fallen yet. MJE's Avatar
    Join Date
    May 2007
    Buzzards Bay, Massachusetts

    just assembled 2 Lowell motors...haven't run them yet...compression question on 1390

    I hit the starter with a compression checker in the machine for a 158 to 160ish with all 3 cylinders on my Lowell ported 1300...

    I hit the starter etc. on my 1390 Lowell machine and receive 125 on each cylinder. The 1390 was nikasil'd and bored through Lowell.

    I haven't run either one of the machines but I was wondering if I have done something wrong or if the nikasil/rings need to set themselves on the "new" motor. The other engine I just changed the rings because I broke it all down, cleaned parts etc. I do know that on the bench the 1390 by hand was near impossible to turn for a cycle vs. 1300 which was slightly less "impossible"..

    Let me know your thoughts...I'm holding off on the exhaust installation until I hear a thumbs up or down.

    BTW there is a rebuilt T+W crank from crankworks in it, 4 degree keyway...Basically all the mods in my sig.


  2. #2
    Happily Self-Employed WFO's Avatar
    Join Date
    Nov 2005
    Houston, Texas
    IMO too many variables to diagnose your problem on here... cylinder bases cut, head size, # of head and base gasket layers, port height...

    Call Lowell and he will get you on the right track

  3. #3
    cigarlust's Avatar
    Join Date
    Apr 2008
    Funky town (Fort Worth TX)
    I know group K's website talks about the compression not reading correctly on their 1390's due to the extra volume when they crank...

  4. #4

    Join Date
    Apr 2008
    Lindenhurst, IL
    When warm i am hitting, 130,130,125 (40cc,40cc,42cc).

    I think the pipes have something to do with the reading, not sure.

    Put em in you be fine.

  5. #5
    Join Date
    Oct 2006
    new builds dont read right when first assembled, they need to be run so the rings seat ....i freaked out with my first build when i cranked it over and it read way low.....after it was run it was up 20psi odd to 140psi

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