still got spark knock

Discussion in 'Engine Topic' started by badazz70z28, Oct 26, 2012.

  1. badazz70z28

    badazz70z28 Veteran Member

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    i put a new dizzy in it, i have tried super unleaded along with octane boost. i did run a compression test and every cylinder was at 100 which seems odd they would all be low, have not done a leak down test yet, but i don't think the low compression is going to cause the spark knock. is there a cure for this big block other then a rebuild ?:mad:
     
  2. sweetsoul

    sweetsoul Veteran Member

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    you know , i have found that on acceleration , and under load a lean condition will cause a spark knock.
     
  3. Damon

    Damon Veteran Member

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    100 PSI in every cylinder? THAT would be the first thing I would chase, not the spark knock issue. They're probably related, but you are way WAY off the bottom end of the scale. A Briggs & Stratton can huff up a 90 PSI reading. My 8:1 blower engine can squeeze 135 with a little bit of a cam in it.

    Now, before we all get our panties in a bunch, please get a different compression gague and try again. Yours may simply be out to lunch. Or, somebody could have replaced the SPECIAL check valve in the end of the hose with a regular tire valve stem check valve which will knock a TON off the observed reading (ask me how I know).

    Let's be REALLY sure you're that low before we proceed. If you are, you got internal engine issues like a cam that's way retarded on something like that which will need to be resolved before you chase this mysterious spark knock (and will, in all likelyhood, fix the problem even though it raises cranking compression).

    What I'm saying is that 100 PSI cranking compression is so far outside what you need to have an efficiently operating engine it could well be causing or contributing to the spark knock issue.
     
  4. Todd80Z28

    Todd80Z28 Moderator Staff Member Lifetime Gold Member

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    Before you do all that- you did have the throttle wide open when cranking for the compression test, correct?
     
  5. cmonson

    cmonson Veteran Member Gold Member

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    Almost sounds like the cam was installed incorrectly.

    Assuming you performed the compression test ok, even with an internal engine damage, the chances of every cylinder being low is slim.
     
  6. badazz70z28

    badazz70z28 Veteran Member

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    thanks for the input guys. the motor itself seems to run pretty good . it does not smoke at all , i was thinking timing chain gears and cam would be a good start.
     

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