Can't stop from Pinging

[Jrwittlin]

Hello,

I am new to this forum but I have been trolling for some time. This pinging issue has got me stumped and I need some of your expertise. I have a lot of engine ping that I can only resolve by retarding the timing a lot (like 20 degrees ATDC).

1979 traveler
345/727
Stock ignition (I think)
Edelbrock 1406 carb (no idea on jets, rods, springs etc.), carb was on it when I got the scout
I “Rebuilt” the engine: New crank, mains, rod bearings (all std size), cylinders within spec, so light hone and new standard piston rings
Did not have the heads redone
NOS OEM gaskets – engine not decked
New 3332 plugs gapped to 0.035”
Compression is 140-150 on all cylinders
Vacuum at idle (~675) is 22”
Engine has about 180 miles since rebuild
Engine runs great except the pinging. It starts easily, runs good, no back firing, no hiccups, no stutter, no ticking, clicking, knocking, nothing, revs excellent, just pings under load or trying to maintain more than 55mph.

What I’ve tried:
Timed using “normal” procedure: No 8 cylinder, timed to 0-5 deg TDC with vacuum advance not hooked up, tighten distributor and hook up the vac advance – engine pings under load
Switched from port to manifold vacuum for advance – engine still pings under load
Disconnected vacuum advance entirely (and plugged open vacuum port so no vac leaks) – engine pings slightly less under load
Retarded the timing (to like 20 deg ATDC) and left vacuum advance disconnected – engine pings very little (but idle is very low, like the engine does not want to be there, but this actually gave it the most driveability of all the settings tried)

What I’ve verified:
Idle vacuum is great (21-22”)
Vacuum advance is working (advances the timing approx. 10 deg when engine is revved)
Mechanical advance is working (advances the timing approx. 15 deg when engine is revved) and the rotor rotates easily by hand, it doesn’t “snap back” though
When timing is set to 5 deg BTDC, total advance when revved is between 30 and 35
Tried timing by using vacuum gauge, pretty much nets me at 0-5 deg BTDC
Idle air screws adjusted 1.5 turns out (also netted the best idle vacuum)
Manually opening the EGR does cause the engine to stumble but stays running

Things I’m wondering (some are getting desperate):
Could I have the cam not aligned – pretty sure I triple checked this during assembly
Could the EGR system be contributing? (when I was assembling the engine I noticed the EGR was stuck open, so lubed it up and got it working. Now it seems as though the diaphragm is junk – I’ve hooked it to straight manifold vacuum and it doesn’t actuate) I do remember the truck not idling nearly as good before I tore it down for rebuild – probably because the EGR was open all the time.
Could having the electric choke hooked to the coil be causing some issues
Could the distributor “fail” in such a way to cause too advanced of timing (funny why not seeing this when revving with timing light – occasionally I did see the timing moving around but never too advanced)?
Are there differences in cranks (crank came out of another 345 I had), and this is causing the crank timing lobe and/or crank to camshaft to be not aligned
If I got some bad gas – I have not drained and tried premium yet

Thank you all so much.

 

[1975IH200]

My comments in red.

Hello,

I am new to this forum but I have been trolling for some time. This pinging issue has got me stumped and I need some of your expertise. I have a lot of engine ping that I can only resolve by retarding the timing a lot (like 20 degrees ATDC).

1979 traveler
345/727
Stock ignition (I think) Find out what you have please. There is a sticky thread on distributors to look thru to determine which unit / system you have.
Edelbrock 1406 carb (no idea on jets, rods, springs etc.), carb was on it when I got the Scout
I “Rebuilt” the engine: New crank, mains, rod bearings (all std size), cylinders within spec, so light hone and new standard piston rings
Did not have the heads redone
NOS OEM gaskets – engine not decked Is the head gasket composite or metal shim style?
New 3332 plugs gapped to 0.035”
Compression is 140-150 on all cylinders
Vacuum at idle (~675) is 22”
Engine has about 180 miles since rebuild
Engine runs great except the pinging. It starts easily, runs good, no back firing, no hiccups, no stutter, no ticking, clicking, knocking, nothing, revs excellent, just pings under load or trying to maintain more than 55mph.

What I’ve tried:
Timed using “normal” procedure: No 8 cylinder, timed to 0-5 deg TDC with vacuum advance not hooked up, tighten distributor and hook up the vac advance – engine pings under load
Switched from port to manifold vacuum for advance – engine still pings under load
Disconnected vacuum advance entirely (and plugged open vacuum port so no vac leaks) – engine pings slightly less under load
Retarded the timing (to like 20 deg ATDC) and left vacuum advance disconnected – engine pings very little (but idle is very low, like the engine does not want to be there, but this actually gave it the most driveability of all the settings tried)

What I’ve verified:
Idle vacuum is great (21-22”)
Vacuum advance is working (advances the timing approx. 10 deg when engine is revved) -This is actually indicating centrifugal advance, not vacuum advance.
Mechanical advance is working (advances the timing approx. 15 deg when engine is revved) and the rotor rotates easily by hand, it doesn’t “snap back” though -Rotor should snap back, clean the advance weight mechanism and lube them.
When timing is set to 5 deg BTDC, total advance when revved is between 30 and 35
Tried timing by using vacuum gauge, pretty much nets me at 0-5 deg BTDC
Idle air screws adjusted 1.5 turns out (also netted the best idle vacuum)
Manually opening the EGR does cause the engine to stumble but stays running

Things I’m wondering (some are getting desperate):
Could I have the cam not aligned – pretty sure I triple checked this during assembly
Could the EGR system be contributing? -Yes. (when I was assembling the engine I noticed the EGR was stuck open, so lubed it up and got it working. Now it seems as though the diaphragm is junk – I’ve hooked it to straight manifold vacuum and it doesn’t actuate) I do remember the truck not idling nearly as good before I tore it down for rebuild – probably because the EGR was open all the time. -Sounds as if the EGR valve is bad, a torn/leaking diaphragm will give you a vacuum leak.
Could having the electric choke hooked to the coil be causing some issues - Yes, definitely incorrect, choke should have it's own power source when the key is in the "ON" position.
Could the distributor “fail” in such a way to cause too advanced of timing (funny why not seeing this when revving with timing light – occasionally I did see the timing moving around but never too advanced)?
Are there differences in cranks (crank came out of another 345 I had), and this is causing the crank timing lobe and/or crank to camshaft to be not aligned -No.
If I got some bad gas – I have not drained and tried premium yet

Thank you all so much.

Correct the above items and report back.

 

[Jrwittlin]

Thank you for the reply.

I have verified that my ignition is a prestolite with pertronix module. I disassembled last night and cleaned and lubed the weights for the mechanical advance, the rotor now snaps back fully. I also ran a separate wire for the electric choke.

I forgot to mention, that when I discovered the EGR was not opening, I disconnected the vacuum (and plugged the line - so I do not have any vacuum leaks - but obviously I don't have a functioning EGR). I will work on sourcing a new EGR valve....

I said my vacuum advance was working because it is advancing during revving and I've sucked on the hose and verified it moves all the way (I also cleaned and lubed the mechanism last night). I have my vacuum advanced hooked to port vacuum so that would advance the timing as the engine rpms are raised. As stated in my original post, I've switched to manifold vacuum with no better result - still pings.

I timed again and took it for a drive - still heavy pings. To stop the pinging I again netted out at about 20 degrees ATDC - so no change.

Please continue to help me....

 

[Jrwittlin]

Update, I misspoke I have a prestolite distributor with the oem electronic module not a pertronix unit.

 

[1975IH200]

Thanks for the distributor photos to verify identification. Photos are always helpful.

How about a photo of the cap & rotor?
Photos of the engine might be helpful as well.

Is the dust cover intact? It is needed for the Prestolite cap to fit on the distributor body properly, without being a sloppy fit.

Install the distributor and time the engine to about 5° to 10° BTDC.

I will attach a .pdf file that you can use to check your distributor, plus an article on engine timing.

 

[Jrwittlin]

Sorry for not getting back to you, I was in vacation with the family. Anyway, I took some pictures of the engine and the distributor. The dust cap is in place and not cracked. The dist cap is also newer and not cracked and fits reasonably tight. Thank you for those manuals, I will do the mechanical and vacuum advance checks tomorrow night. I am honestly leaning toward a faulty timing gun. Mine is a hand-me-down that has had a hard life and been dropped more than once. The scout now starts very easy when warm with the timing retarded (as my light tells me anyway). I am getting a new light tomorrow and will verify and do the tests you sent me.

 

[Jrwittlin]

Pictures of the engine

 

[Hondo]

Might have missed it, but what octane fuel are you running, and have you tried any octane booster? If you look in one of the owners manuals, they recommend "regular gasoline of 92 octane or better".

 

[Scoutboy74]

These are low compression engines. High test is meant for high compression engines. Unless the compression ratio was dramatically increased via machining, it should be able to run just fine on regular, if not mid grade.

 

[Hondo]

Yeah I know, but running higher octane wont hurt anything but your pocket book. The pinging/detonation on the other hand can do extensive damage if allowed to continue. Adding a bottle of octane booster, or adding some premium is a quick, not too expensive sanity check. Don't know about his different crank question, but getting #8 piston at TDC on the compression stroke and pulling the distributor cap to make sure rotor is pointed directly at # 8 plug wire location wouldn't be a bad idea. I've seen dampers slip on the crank hubs before.

 

[Jrwittlin]

Hi Guys. Thanks for sticking with me on this. Hondo, I am running premium ethanol free 91 octane. Between me retarding the timing and the high octane it is no longer pinging but obviously is still not right.

Last night I tried a new timing light and got the same reading so that theory is busted. I conducted the tests to check the mechanical and vacuum advances. To start I set the timing from my retarded setting to 0 degrees (to make the tests "cleaner" (no math involved when starting from 0). Timing was set to 0 with vacuum advance disconnected.

Immediately the idle picked up (as expected) but the engine idled less smooth. It wasn't shaking or studdering, just not humming along smoothly like it does at retarded timing. It had a sort of small occasional miss. Non the less, I set the idle to 680 and proceeded with the checks.

Mechanical advance check:
At 680 timing = 0 deg, manifold vac = 21"
At 1000 timing = 3 deg, manifold vac = 21.5"
At 1500 timing =10 deg, manifold vac = 22"
At 2000 timing = 15 deg, manifold vac = 21"
At 2500 timing = 19 deg, manifold vac = 21"
At 3000 timing = 25 deg, manifold vac = 20"
At 3500 timing = 28 deg, manifold vac = 19"

Vacuum advance checks: idling at 690
At 0" timing = 0 deg
At 5" timing = 5 deg
At 7" timing = 7 deg
At 12" timing = 7 deg

 

[Jrwittlin]

Also I forgot to mention that the Scout started very hard when warm when set to 0. It turmed over very slow (like classic too advanced timing). It starts very easily warm and cold with the timing retarded.

 

[Scoutboy74]

That doesn't make any sense. Timing measurements were taken from wire #8? I think like Hondo suggested, you need to re-examine your distributor stab and plug wire routing.

 

[Jrwittlin]

I've already verified the order of my plugs on the cap and that the wires go to the right cylinders. Yep, timing on #8.
I will triple ck the distributor. I am able to achieve the correct timing off #8 it just doesn't like to run there. If I am able to obtain the correct timing does that not mean that my distributor is stabbed correctly? I will verify that it is at tdc on #8 and that it is pointing to #8 on the cap tonight. Thanks for the suggestions, keep them coming.

 

[FDChappie]

It might be time to remove the spark plugs, set #8 on TDC compression stroke and see if the timing mark aligns with 0.

 

[Robert Kenney]

A couple of things. Basically pinging is the combustion pressures reaching the critical pressure before the piston is far enough passed tdc and on its way down. Either reduce burn rate or ignite the fuel air charge later.
1) The introduction of exhaust gas by the EGR valve into the air charge, reduces burn rate and combustion temperatures. This reduces pinging. You should have it working or recurve the advance curve in the distributor.
2) Significantly advanced cam timing will increase cylinder pressures and burn rates enough to effect pinging. Do you have any information regarding the cams installed position. Possible that is a tooth advanced.
3) How old is the fuel? Make sure it is fresh. Not old gas with some new on top. I have had old fuel (2 months) lose octane in my stock scout so far that I had to drain it to stop pinging.

 

[Jrwittlin]

Problem solved! And I'm an idiot. I was using the leading edge of the lobe of the harmonic balancer not the timing line. This completely explains why I was "retarding" the timing alot to make it idle and run well (and stop pinging). Turns out that using the timing line I had the initial timing around 20 deg BTDC where it was no longer pinging (what I thought was extremely retarded was still aggressively advanced). I now set it to 12 deg BTDC (using the timing line).

I will try to save face: I missed the timing mark because it was very faint and painted over. When I initially stabbed the distributor and hooked the timing light up the leading edge was the only indicator I saw so i went with it. I figured this out when I was comparing the harmonic balancer from the donor engine and saw a very pronounced timing mark, I then inspected my harmonic balancer and sure enuf there was a very faint line......I highlighted the heck out of the line now.....

Man I feel like a dumbxxx, I am embarrassed to say the least. I share my woes in case someone else can learn from my mistake. Also I owe it to everyone that has helped me. All your advice was spot on! And was what made me check the harmonic balancer.

On the plus side I now have a great running Scout and an ignition that has been cleaned and tested and I've learned a ton.

I cannot thank you guys enuf. I only feel bad wasting your time.

 

[Scoutboy74]

You didn't waste our time. That's an honest mistake, although it is the first time I've heard of it happening in my nearly two decades of playing in this sandbox. No harm was done. It was a bit of a learning experience for us as well. I'll tuck this away for future reference in case someone else has a similar issue. I suppose if it can happen once, it can happen again. Good job resolving it and especially for updating us.

 

[Robert Kenney]

Good news...
Funny, I'm heading out to verify the timing marks I created when building the 409 in one of my jalopy's. I had degree tape on the balancer but it departed at some unknown point.

 

[FDChappie]

Good to here the problem is resolved. Thanks for letting us know what the issue was. ;-)