500 massive pinging!!!
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500, 472, 425, 368 Discussion, 500 massive pinging!!! in Cadillac Engine Technical Discussion; Hi guys. Recently did a full rebuild on a 1973 Eldorado 500 convertable. Broke it in real easy, then noticed ...
  1. #1
    lessloop is offline Cadillac Owners Member
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    Unhappy 500 massive pinging!!!

    Hi guys. Recently did a full rebuild on a 1973 Eldorado 500 convertable. Broke it in real easy, then noticed severe pinging when I put my foot in it. Pulled timing advance back some, no change. Then pulled base advance back to 0 degrees. No change. Swapped distributors, timing at 0, plugged vacuum advance. No change. Added octane booster to fresh premium fuel, no change. EGR valve is brand new from NAPA and hooked up. The rebuilt long block from is from S&S Engine in Spokane WA. Don't think that matters except to mention that my original block and heads which never did this, (15 years ago), went away as core return. Rebuilt air pump- all smog stuff new/ rebuilt and hooked up as far as I can tell. New/ rebuilt carb, new fuel pump, new or rebuilt everything. Pinging is so severe that the car is undrivable.
    Any ideas?!!!

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  3. #2
    Submariner409's Avatar
    Submariner409 is offline If it won't run, chrome it
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    Re: 500 massive pinging!!!

    It has to be something wrong with the EGR.

  4. #3
    deVille33 is offline Cadillac Owners Connoisseur
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    Re: 500 massive pinging!!!

    Were the heads resurfaced? Correct pistons installed? Was detuning started in 73 or 74? I recall compression ratios were changed somewhere in that time era.

  5. #4
    lessloop is offline Cadillac Owners Member
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    Re: 500 massive pinging!!!

    I bought a rebuilt long block from S&S Engine < http://www.rebuiltautoengines.com/ > who make big claims about the quality of their builds. This car ran perfectly with all smog, including EGR, diconnected 15 years ago.

  6. #5
    The Ape Man's Avatar
    The Ape Man is offline Cadillac Owners Connoisseur
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    Re: 500 massive pinging!!!

    One time I needed a fresh engine fast for a customer. The rebuilder sent a long block with dished pistons bolted up to open chambered heads. Very low compression. The thing ran really poorly.

    You could have landed up with flat top pistons and closed chambered heads which gives over 12:1 compression ratio. The engine would be difficult to start when hot and ping. Been there too.

    Not saying this is your problem....

  7. #6
    lessloop is offline Cadillac Owners Member
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    Re: 500 massive pinging!!!

    Wow. Very interesting. I suppose a compression check would tell the story there, right?

  8. #7
    carnut is offline Cadillac Owners Master
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    Re: 500 massive pinging!!!

    An aftermarket generic EGR valve can do this. One size does not fit all.

  9. #8
    steelybill is offline Cadillac Owners Enthusiast
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    Re: 500 massive pinging!!!

    The '74 had odd-ball pistons from what I remember, but the '73 shouldn't be that way. Some mechanics have a boroscope, to look into the cylinder through the spark plug hole, which may be a way to dee and identify the top of the pistons. The '73 is supposed to have a "soap dish" shaped dish, while the odd '74 has flat top pistons. If yours has flat top pistons with the '73 heads, it might be the problem, since without the dish, the comp ratio will be higher than stock '73 etc.

  10. #9
    drmenard is offline Cadillac Owners Enthusiast
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    Re: 500 massive pinging!!!

    It looks like to get to the bottom of this you are going to have to take off a head to see what you have..Large or small chamber heads? What dish pistons... how much was milled off the heads? and the type of head gasket ? How thick is the compressed gasket? All these things can cause this type of problem...

  11. #10
    steelybill is offline Cadillac Owners Enthusiast
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    Re: 500 massive pinging!!!

    The so-called rule of the thumb is : "don't mix early heads with late pistons" 12:1 ratio will be the likely result..
    The head number may be visible with a valve cover removed. The small chamber heads numbers end in 250, 902, and 950. The late large chamber heads end in 552, and 493. The position of the Caddy spark plug holes are sort of visible enough to maybe get a look at the top of a piston....not sure, but worth a try...

  12. #11
    70eldo's Avatar
    70eldo is offline Cadillac Owners Connoisseur
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    Re: 500 massive pinging!!!

    If the rebuilt has the high compression you will need premium gas!

  13. #12
    The Ape Man's Avatar
    The Ape Man is offline Cadillac Owners Connoisseur
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    Re: 500 massive pinging!!!

    I put one together on purpose with high compression. It was a bear to keep happy. May be more like 12.5:1.

  14. #13
    GM_Parts_Guy is offline Cadillac Owners Member
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    Depending on the compression you may need more than premium meaning race fuel. Suggest you pull er apart and figure out exactly what you have.

  15. #14
    cadillac_al is offline Cadillac Owners Connoisseur
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    Re: 500 massive pinging!!!

    A simple compression check might shed some light on the compression; especially since we aren't dealing with a wild camshaft. Most smog engines have 130-150 compression and older high performance engines can crank in the 180 range. If you really had mismatched heads and pistons I would think the compression gauge would read considerably over 180.

    It sure is puzzling since you dialed back the timing so far with no change.

  16. #15
    The Ape Man's Avatar
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    Re: 500 massive pinging!!!

    Another clue is the engine will be difficult to start when heat soaked especially with klodrajet leaky fuel bowls.

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