Pinging - is my cam the problem?

Discussion in 'Engine Topic' started by Marty Burks, Jul 22, 2021.

  1. cadillac_al

    cadillac_al Veteran Member

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    It sounds like you just need to play with it. You could slow down the mechanical advance with stiffer springs or limit the vacuum advance or buy a vacuum can closer to what you need etc. What rpm is it pinging at? Is it just lugging at low rpm's?
     
  2. sandlapper

    sandlapper Veteran Member

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    True TDC is only when #1 piston is at mid-dwell & while at top of bore; best measured w/ bridge dial indicator. Afterwards, a plug-piston stop will do.

    Perhaps the damper's outer ring with zero aka TDC groove is Not properly located in reference to keyway ... maybe wrong damper ... or if damper Not New, its outer ring may've slipped.

    Sometimes, the timing TAB is Not matched to the damper; happens a lot.

    If any of those, the TDC reference groove is in wrong location and then all else which depends on that is "off" as well. This sort of error can be detected during a proper cam degree procedure.

    Also, some "dial-back" timing lights have acquired the dubious distinction of being wrong.

    Also, some CD boxes induce a wrong advance/retard.
     
  3. 1980RS

    1980RS Veteran Member

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    Here is something I will toss out there, Get a dial back timing light, make sure the total is what DUI says it is in the dizzy. You would be surprised what you find also make sure you disable the MSD is you are running one. I am having a tough time with the combo you have that it ping this much and it you ran a total of 32° and it still pings I would get some non-oxy fuel and try that as sometimes there is a lot less in some premium then is in the stations tanks. Fuel from another place is an easy test. Best timing lights for me are the old Craftsman ones, I have a total of $6 in two of them and my high buck Snap On is in the box collecting dust as it's inaccurate.
     
  4. COPO

    COPO Veteran Member Lifetime Gold Member

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    Post #1 says no vacuum can is being used.
     
  5. cadillac_al

    cadillac_al Veteran Member

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    Post #10 mentions adjusting the vacuum pot. :)
     
  6. COPO

    COPO Veteran Member Lifetime Gold Member

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    Weird
     
  7. jeff swisher

    jeff swisher Veteran Member

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    I am curious as to what the cranking pressure is.
    Not that it matters but if it is stupid like 260 PSI you do have an issue.

    I have ran 245 psi on 91 octane without issue.

    Piston .010" down the hole and thin steel felpro head gasket.
    That could be the .015" head gasket and giving you .025 piston to head clearance.

    I have ran .028" piston to head on a 355" without much issue but when i stuck a .039" head gasket on it ran exactly the same.
    BUT!!! When the outside temps got around 90 I had to play with the timing and jetting a smidge on the steel shim set up.
    With the thicker head gasket it was not finicky.

    Last thing.
    Are you sure it is pinging you hear?
     
  8. 2ndGenCrazy

    2ndGenCrazy Veteran Member

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  9. FS87LT

    FS87LT Member

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    If all else might fail, head to the salvage yard and look for a earlier-'80s Chevy pickup that was a V-8 with "Electronic Spark Control" nameplate on the tailgate. Once found, remove the glove box and then remove the silver box adjacent to it AND all of the attached wires, all the way to the distributor and rh engine block. Get a new ign module from a parts source for that year of pickup, as it has more terminals. One wire should go to the detonation sensor on the rh side of the engine block (screwing into the rh block drain plug hole).

    This system is a free-standing detonation limiter system that was OEM on several model years of GM full-size pickups in the earlier 1980s. One of those little things that seemed to get overlooked, it seems, but allowed for the 9.5cr 305s that were in the pickups back then. The test of system functionality is to tap an exhaust manifold with a metal wrench, as the engine idles. With each tap, the timing will retard. Enough taps and the retard will be enough to kill the engine, just as a thumping main bearing will also do.

    As to the particular engine combination of parts . . . everything is oriented toward building more cyl pressure, which can effectively increase the CR in certain rpm ranges via better "cyl filling". 4degrees BTDC is not too low of a base idle timing setting, as that was used on many emission-controlled 350s in the earlier '70s, but a bit higher is usually better. Just adjust the idle mixture and speed to compensate for it.

    Spark plug heat range probably needs to be a bit colder than an AC R-44S heat range or equivalent, I suspect. Maybe down to a R-42S? I know, the extended-gap S pliugs were usually not OEM spec, but I like them better as it puts the spark nearer the center of the combustion chamber and effective advances the timing a few degrees over what it would effectively be with a non-S plug. Key word is "effectively" as combustion happens "in total" sooner than if the spark originates at the edge of the combustion chamber.

    How are the plugs coloring? If things are too lean, there's a ceramic color for that.

    If you read David Vizard's book on Chevy cyl heads, he mentioned a certain distance between the piston crown and the edge of the cyl head that tends to kill detonation possibilities. As if that distance relates to a "resonant frequency" of sorts that kills detonation.

    On the surface, the cam specs don't look that flaky as to detonation tendencies, BUT the intake valve opening point might be the key. Although we are used to seeing modern engines with 11.0CR, we also need to understand that they are highly "electronic'd" and most probably have a later intake valve opening point than older engines tended to. Which means they still have their high static CR, but compress a bit less air/fuel mixture in the process.

    As a final test, head down to a regional race fuel distributor and get some 100 RESEARCH octane racing fuel. Octane level is more important than lead content, in this case. Add 5 gallons into your normal fuel for a full fuel tank and see what happens. If the ping goes away/diminishes with more higher-octane fuel, then you have your answer. Get the vehicle onto a chassis dyno and fine-tune the fuel/spark maps with the no-clatter racing fuel. Then decrease the race fuel additions and move backward with the timing settings.

    As for the supplied advance curve, a SBC usually likes 38 degrees BTDC total timing at 4500rpm or so, but that might decrease a few degrees with better cyl filling from aftermarket heads. Racers ususally like to see that rpm be 3000rpm, though. By observation, what DUI and others supply is more generic rather than specifically tailored to each engine their distributors might be placed in. In other words, it's good enough to get you started, but the owner will need to fine-tune it to work best in their engine combination of parts. Whether than be for total advance of part-throttle advance via an adjustable vac advance can.

    Remember that a Pump Octane of "91" Super Unleaded is pretty much the same Research Octane we had with 95 Research Octane "Regular" fuels in the 1960s and earlier 1970s. With the 1974 Pump Octane of 95 equating to Research Octane of 100, back then, which is what advertised 9.6+cr 4bbl engines needed to not clatter anytime.

    A 180F degree thermostat is key, too. As intake air temp being a contributor, too.

    Sorry you've got this problem, but I also susepct it'll take some time to get the combination "dialed-in", rather than "plug 'n play".

    FS87LT
     
  10. Marty Burks

    Marty Burks New Member

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    Sorry about the confusion on the vacuum pot. I have done quite a bit of fiddling up to this point. When the pinging became my major problem with this engine, I disconnected the vacuum advance and worked with just the mechanical timing. I have checked the centrifugal advance on the DUI (I also use a craftsman dial back timing light) And it shows to be 24 Degrees just like DUI says and its marked on the bottom of the dist. by them. I eventually got to about 6 BTDC where it still ran OK but not great and still pinged and lugged the starter, any slower than that setting and it idles rough and is pretty sluggish. I bought an adjustable vacuum can with the idea of setting the initial lower, like 4, and adjusting the vacuum to add 2+ degrees at idle using the manifold vacuum port. As you can see, at this point I'm really grasping at straws. In any case, that helped the starting, it still pings and it is pretty sluggish but idles ok.

    To another point, the dampener is new and I checked the marking with a dial indicator before installing the heads so I think that the TDC mark is ok. At this point though, I'm making most of my changes 'by ear', just using the timing light to keep track of where I have been. I will check the cranking pressure in the next few days when I can get the time and report back. I have a hunch that It will be high as Jeff and 2GC suggested. Thanks again for the responses.
     

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