Okeh, I've got an interesting mystery on my hands, and my ability to mentally keep track of theoretical effects of different valve timing is limited at best.

'73 Dart, basically stock, just under 55k original miles. Over 9/16" of crank pulley rotation before distributor moves, the last time I checked, and I'm sure it's getting worse -- timing chain is slack; cam is at least 5° retarded. Seems to me that should greatly reduce cylinder pressure, making it difficult to get the engine to ping, but this thing pings very badly at highway speeds under any but the lightest throttle pressure. Regular or high-test gasoline doesn't matter. Retarding the base ignition timing doesn't help. Four different distributors with curves ranging from short/slow to long/fast do not change it. There are no vacuum leaks. EGR is not present, but that's been the case on most other slant-6s I've driven regularly. I suspect restricted exhaust (muffler rattles loudly, and that's on top of stock 1¾" pipeworks), but here again…this much pinging with that much cam retard? I am sure I'm missing a big, obvious chunk of the picture here. Someone point it out for me?

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

Most slants I've owned which pinged also used oil past the rings. They didn't smoke, but the used oil and pinged on the highway when accelerating.

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Joshua

Well, it's soon to be a moot point (as you know! ) but I'm still curious. Seems to me it'd need to be drinking a lot more oil than it does to lower the effective octane rating far enough to cause this much pinging, but I'm running short of ideas and yours is certainly realistic. Thanks for comment.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

Hi Dan,
Maybe carbon deposits in the combustion chamber...did you try cleaning them out with water/steam or parts store cleaners?

Intake air temp, too hot. Manifold heat control stuck Air cleaner vacuum diaphragm in heat mode under high vacuum conditions.

Moot point?

CJ

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Part of Tyrde-Browne Racing

Your moot points need sharpening......


A slack timing chain will increase cylinder pressures at lower RPM.

I agree with Josh on oil and pinging.

It takes 2 hours to change a chain.

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Yeah....Im the one who destroyed this rare, vintage automobile.....

???

Last time I checked, retarded (late) cam timing REDUCED cylinder pressure - less power/torque at LOW rpm, more at HIGHER rpm.

Most of the usual suspects have been covered. : Manifold heat riser valve, thermostatic air cleaner, exhaust restriction, lean run condition, incorrect spark plug heat range, oil/ carbon buildup, eng overheat condition.

I'd go after the exhaust first & recheck. The thing about ping is once it starts you need to pull LOTS of timing out to stop it. (ie, if you ping because of 2 degrees overadvance, you have to pull at least 8 degrees to stop it) If your fault isn't a timing issue, timing will have little effect- retarding timing will reduced peak cylinder pressure & temp but ends up putting more heat into the exhaust system.

You could also do compression tests , both during cranking & running ( at idle you should have about 1/3 of your cranking #'s) - that should show if there is a gross cam timing issue.

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63 Valiant Wagon
225 - 4 bbl

I am trying to resist going back to drinking coffee.
How? Walk me through it, willya? The cam is retarded relative to the crank, so every valve event happens later than it should. The intake valve opens later (so less mixture inducted) and closes later (so some mixture pushed back out the intake valve); the exhaust valve opens later and closes later...all of that suggests lower cylinder pressure at low RPM to me; what am I looking at the wrong way?

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

Combustion chambers were thoroughly manually cleaned when I had the head off last September. Right down to shiny bare metal. Coolant passages in the head were acid-cleaned, too. Minimal change in ping. Good thought, though.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

None of the above, but good thoughts.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

Better motor in the offing.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

If you have that much slack you can jump a toothertoo. If it jumps like the Valaint did you end up with fantastic idle.....massive low end torque and an inability to rev past 1800 rpm and pinging under load. I drove home 100 miles on a 100degree day in 5th gear at 30mph.

Depends if it jumps on accel or decel.......


Have you checked cam timing?

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Yeah....Im the one who destroyed this rare, vintage automobile.....

I don't have any of those things.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

Fuel aint no good













Ron Parker