Fresh Engine. Low Compression

Discussion in '1979 - 1995 (Fox, SN95.0, & 2.3L) -General/Talk-' started by a91what, Apr 15, 2014.


  1. a91what

    a91what Member

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    ok so i have a huge problem. my new 306 ran great on initial start up but now the cylinder walls are washed down.... 30lbs of compression on new moly rings. I am hoping some of the gurus out there have some special trick to get them to come back. i really dont want to pull it back out and rebuild it again. rings were sealed power moly. i made sure to install them dot up and clock the intermediate ring 180* from top ring.

    Thanks
    #1
  2. RangerJoe

    RangerJoe Advanced Member

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    First off, how are you performing the compression test? Are you using the starter to turn the engine over, or are you doing it by hand? If by hand, you will never get good numbers out of it. You will have to use the starter. If they are washed, my buddy used ATF fluid on his four wheeler to accomplish resealing. I believe he poured it in and let it sit over night.

    Keep us up to date, and good luck.

    Joe
    #2
  3. 84Ttop

    84Ttop They make new pistons every day, so why worry? SN Certified Technician Mod Dude

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    I've used marvel mystery oil once to get some ring seal back in an old junk yard motor. If it is a new motor, the right way to do it unfortunately is to pull it apart and hone the cylinders re gap a new set of rings and re assemble...
    #3
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  4. a91what

    a91what Member

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    well i just built it i honed the block and cleaned it before assembly. i used a regular ball hone 5-6 passes with some oil for lube. the car ran great then it just stopped. i literally fired it up twice once to set timing and adjust the idle the second time was to check my t-5. the third atempt was a failure which resulted in the test. 30lbs with starter turning it over, then put air on the cylinder 150psi from compressor and noticed air in thecrank case. i guess what im asking is do i need to rip it all back out, i have never had this problem before.
    #4
  5. 84Ttop

    84Ttop They make new pistons every day, so why worry? SN Certified Technician Mod Dude

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    Are the chamfers on the rings installed correctly? Just a thought...
    #5
  6. Bullitt347

    Bullitt347 man bewbs please...

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    If the ball hone you used is too coarse then you may have wiped out the rings. Modern rings like a very fine finish on the hone job. Typical ball hones are way to coarse to do the job correctly. In fact I have yet to find a commercially available ( auto parts store) ball hone that was fine enough to do the job right.
    #6
  7. 84Ttop

    84Ttop They make new pistons every day, so why worry? SN Certified Technician Mod Dude

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    I want to say my ball hone is 400 grit.. I had to order it but I've re ringed a few stock 302's with it and never had any trouble. I know what you mean though, most cheap autoparts store hones are 80 or 120 grit.
    #7
  8. DesertDawg

    DesertDawg Member

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    All eight cylinders are at thirty pounds? ;) j/k
    "my new 306" why'd you re-ring a new engine?
    This one is a good example of: when troubleshooting ask questions before providing answers.
    "well i just built it" (read before answering)
    I don't have a full set of micrometers and my own machine shop guess I'm not an engine builder

    this one has me wanting to ask more questions than I'd have answers for heh heh
    #8
  9. FoxMustangLvr

    FoxMustangLvr Mustang Master

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    :scratch::shrug:
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  10. 90lxcoupe

    90lxcoupe Mustang Master

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    How exactly did you do that?
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  11. a91what

    a91what Member

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    Full rebiuld balanced assembly kings bearings ported gts ported cobra intake, block bored .030 reused feom previous build.
    This is not my first build but it is the first time iveused moly rings.

    Keep the smart ass comments in the honda forums please.
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  12. FoxMustangLvr

    FoxMustangLvr Mustang Master

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    Are all the cylinders coming in at 30#? If so then i'd tear it down and inspect. I doubt your going to find a 100psi fix without going back inside and actually fixing what's wrong. It's either a bad hone or wrong rings is my guess.

    How did you break in the motor?
    #12
  13. DesertDawg

    DesertDawg Member

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    oh yeah ok then I'm a goin' with MustangLvr
    tear er down!
    #13
  14. a91what

    a91what Member

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    veried the rpm tl she got hot
    #14
  15. FoxMustangLvr

    FoxMustangLvr Mustang Master

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    Have you drained the oil to see if anything is in it?
    #15
  16. DesertDawg

    DesertDawg Member

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    cut open that oil filter fulla bronze?
    #16
  17. a91what

    a91what Member

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    no but i will today. im gonna try tranny fluid on top of the pistons. there is a strong smell of fuel in the oil. so wash down is a likly culprit, cheap oil change and hope like hell it works.
    #17
  18. DesertDawg

    DesertDawg Member

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    gas in the crank? this is getting weirder by the minute
    #18
  19. 90lxcoupe

    90lxcoupe Mustang Master

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    Is your name Richard by chance?
    #19
  20. a91what

    a91what Member

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    ok no damning evidence in the oil. it was slightly off color darkish looking but still clean, very thin from fuel. the fiter had some shinny silver metallic in it not a ton but enough to bother me. im hoping its just from the bearings the kings are all babbot.
    #20

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