Very large beaver dam, Stan!
All the usual ones, yes.
It is not an exhaust leak, and it is not a mechanical rattle or anything else...it is ping/preignition/spark knock.

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

Ok, in that case, I'll stay tuned.

Dan, you say this is a situation that over time has deteriorated, so clearly it involves parts that has been worn over time. Forgive me for sounding like a childrens teacher using simplified terms here, given more time I could find the correct technical terms.

A knock or ping is a combustion cycle that starts normally, but ends with a flare-up, often because still unburnt fuel comes in contact with a hot-spot. Not powerful or fast enough to be a detonation, but a rapid combustion that causes the pinging noise. I think we safely can eliminate the hot-spot theory in your case. Just the fact that the process happens at the end of the combustion cycle, and we probably have some wear of parts in the equation, leads me to think that increasingly worn piston ring lands in the piston may be the cause. The pinging happens when the piston is on it's way down in the cylinder, otherwise it would be pre-ignition, and that normally happens only once - then finito engine! When a cylinder is worn enough that you can feel the ridge in the cylinder wall where the piston rings turn direction, it is also where the cylinder is most worn, and from that point and down along the cylinder wall, you will have a slight taper. Fuel mixture entering the ring lands because of wear, will be 'squeezed' out from under the piston rings as the piston travel downward into the zone with less cylinder wear, and may cause a rapid combustion when igniting as result of being exposed to the last part of the normal flame front. The situation will worsen as the wear increases, both because the taper in the cylinder will become more prominent, and because the ring lands in the piston may hold more unburnt fuel.
To eliminate other causes, it would be very interesting to get a readout of a O2 sensor before you tear the engine apart.

That's as least a 3¢'er.

Olaf.

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Aspenized

It may not point out the cause but it supplies a solution......

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

Hey, I think I know what the problem is: the motor's broken!

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

Good thing it's your thread Dan, otherwise you know what a response such a flippant remark from someone else would have gotten...

Olaf.

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Aspenized

Dan, I said an O2 sensor reading would be interesting, after thinking things through, a reading of the exhaust's CO-contents would be equally - or maybe even more - interesting. The CO - carbon monoxide - is the result of incomplete combustion. Some of the things auto makers have done to eliminate as much CO as possible, is to clean up the combustion chamber to avoid pockets and 'cold spots', and to eliminate or reduce piston valve pockets, and to move the ring lands closer to the top of the piston, and also reduce the height of the piston rings and the size of the ring lands in the piston, all done to eliminate any 'pockets' where unburnt fuel can 'hide'. In older engines, like the SL6, there was really not much consideration about such things at the time of construction, compared to modern engine designs. Some, to meet the standards of the day, but no more than necessary.
The more I think about your pinging situation, the more I feel that the cause may be as I described in the post above, it fits the design and it may explain how and why. At the time of dismantling the engine, it would be interesting to know if the piston has 'ragged edges' above the top piston ring.

It would be interesting to hear if someone else has seen the phenomena in their pistons taken from a pinging engine.

Olaf.

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Aspenized

Ive heard a bad thrust bearing make those noises before....

~RDE~

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1984 D100 Shorty Custom
Certified Auto Appraiser - RevItUp Classic Appraisals
President - Cherry City Bombers CC
Part of Tyrde-Browne Racing

dan why not open the hood start motor and video record the sound and post here...youtube it..

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slant six's RULE!
http://www.usajon.com

They look beautiful. Evenly light tan across the board. Just replaced NGK #5s with colder NGK #6s before a Seattle-Portland-Seattle run. Zero difference in ping. Also ran high-test fuel: zero difference. Also checked carefully for vacuum leaks and found none.
It'll sit there idling (roughly) at 17 inches' vacuum. That's about 3 or 4 inches lower than what I ought to be seeing at sea level with stock cam.
A quart every 3500 to 4000 miles. I just realised I picked up a bad habit of my grandfather's and missed an oil change; I was past overdue. Changed it today in Portland before heading back up to Seattle. No change in ping.
Ain't got. At this point about the only factors left are the internally-broken muffler putting up a hell of a rattle-racket, and the slack T-chain. I will squash those bugs and keep everyone informed.

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

Because the sound is audible only at highway speeds under road load, and will not record well enough to be useful.

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

Dan,

So you have this engine timed around zero degrees initial?
and running a 15R governor?
with a total initial and mechanical at 30 degrees?

What is stamped on the vacuum pod 8.5R or 11R?

The old worn out barn find (which is a stock 79 SL6) that I am running currently while updating my good motor, I had to go the UR6 plugs with a .035 gap, not the .045 like I was running. I also had to turn the vacuum pod out (CCW) 5 turns to keep it from adding more timing to fast. It had a nasty rattle under load at cruise on hot days. I also built another aluminum heat deflector to put under the carb to keep the fuel bowl cool and a air dam to push more air up into the radiator. After a long run on a hot day the bowl stays luke warm now. I also went to 10 - 40 oil and the pinging has gone away. The 0-30W wasn't providing enough compression. This motor is really weak.....and touchy with regards to tuning.

My 9.5 to 1 motor never gave me this kind of grief..... Hope something will work for you.....until it can be rebuilt.

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Aggressive Ted

http://cid-32f1e50ddb40a03c.photos.live ... %20Swinger


74 Swinger, 9.5 comp 254/.435 lift cam, 904, ram air, electric fans, 2.5" HP2 & FM70 ex, 1920 Holley#56jet, 2.76 8 3/4 Sure-Grip, 26" tires, 25+MPG

Tinnitus?

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66 Lil' Red Piggie Valiant (Mater Crusher) - Thanks Zilla!!!!! 72 Demon (Number 1 Son's)

No...if I time it anywhere near TDC, it'll scarcely start and run and is dangerously sluggish in traffic. I've got to get that timing chain swapped.

I have tried three or four distributors with everything from slow/short to fast/long mechanical and vacuum advance curves. Have tried disabling the vacuum advance. Have tried running high-test gasoline. The pinging remains. I should probably quit griping about it until I swap the T-chain and replace the exhaust system.

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

Dan,

You know that is pretty funny because I thought the same thing and cut off my old muffler and ran 2.5" pipe and new muffler and I swear it picked up a little more pep. Before it was probably putting out 30 Hp at 2000 rpm. Running a stock exhaust system made it cranky and severely pinged, gutless ......the new system feels like I just added another 15 to 20 HP. Mileage jumped from 18-19 up to 22.5 mpg.

Replacing the timing chain should help immensely. Bite the bullet....and do it!

Let us know the rest of the story.........

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Aggressive Ted

http://cid-32f1e50ddb40a03c.photos.live ... %20Swinger


74 Swinger, 9.5 comp 254/.435 lift cam, 904, ram air, electric fans, 2.5" HP2 & FM70 ex, 1920 Holley#56jet, 2.76 8 3/4 Sure-Grip, 26" tires, 25+MPG