The Stovebolt Site Forums The Shop Area Engine Shop Pinging under load

My 1946 216 runs just fine as long as it’s not stressed, but when it’s under load going uphill it pings like mad, sounding like the whole thing is going to rattle itself to pieces.
I’ve adjusted the valves to be.008 and .015
It’s timed at 10 degrees BTDC to suit the 98 octane fuel.
10 degrees is where it runs best but more or less advanced doesn’t make any difference to the pinging.
I’m running out of ideas but I’m wondering if a colder spark plug would make any difference.

Thanks for your advice
Bob

Start from scratch with the basics. It's not a performance engine. Set the timing to the factory specs shown in the manual. Install the correct plugs, AC-43

Make sure your vacuum advance is functioning properly.

I have started from scratch with the basics. At the recommended 5 degrees BTDC it runs like a dog.
And that is the plug I’m using. Well, the NGK equivalent
And the vacuum advance is good as is the centrifugal advance

What method are you using to set timing? If you're using the BB on the flywheel, it might not be in the right position.

Verify TDC on #1 plug manually by removing the plugs and turning the engine by hand until #1 is at TDC. Put our thumb over the hole or take the valve cover off and watch the position of the valves.

I’ve never had any luck with those methods so I just take the plug out and look in to see when the piston is at its highest point. That is about 2 degrees after the U|C mark. On my flywheel the BB is 5 degrees BTDC. So I guess it’s actually only 3 degrees, which would mean my timing is set at 8 degrees BTDC

Use the positive piston stop method to determine true top dead center. Every camshaft manufacturers' setup instructions include detailed procedures for finding TDC. Then use a delay flash timing light to measure the advance accurately. Like the slogan Sun Electric Co. used to put on all their test equipment- - - -"We Test, Not Guess!"
Jerry

As I understand it, looking to see when the piston is at its highest point is the same as the positive stop method. Isn’t it?
The funds don’t quite stretch to one of those delay timing lights at the moment. They’re pretty expensive

The piston will be at its highest point twice in a cycle. Compression stroke and Exhaust stroke. You don't want to mark TDC on the Exhaust stroke.

I guess it sort of depends on your definition of "expensive".

www.ebay.com/itm/204529185723?

Jerry

Why not? The pistons (1 and 6) will be at the same position regardless of the valves. I can do just as good a job of setting ignition timing with the light flashing on #6 cylinder's spark as I can on #1. I've won a couple of $100.00 bets by doing that.
Jerry

At the moment that is expensive.
I’ll see if I can borrow one.
In any case, it runs just fine the way it is, except when it’s going uphill. Should I be advancing it more or less?

OK. I defer to your experience.

Less- - - -a lot less. "Ping" is detonation, which deflects piston ring lands, breaks piston rings, and burns holes in pistons. Gasoline engine detonation is the most destructive non-nuclear power known to man. Just a few seconds of detonation during a dynamometer run I was doing on a MOPAR 440 at 6500 RPM and 714 HP burned a hole in the top of a piston over an inch in diameter. A very lean fuel/air mixture will detonate regardless of where the ignition timing is set. Try using a little choke to richen the mixture when the engine starts to detonate and see if the noise reduces or stops.
Jerry

Your advance mechanisms may be advancing too much. &/or too soon. Weak or a broken spring on the centrifugal advance, or faulty vacuum advance can cause that.
Try driving with the vacuum advance disconnected & see if it makes a difference.
You need less advance. Too much can cause pinging like you are referring to. Its possible the head has been cut down too much giving an excessive high compression ratio.
Don't keep driving like that, you can destroy the engine.

George

Ok, but I don’t understand how it is running good at all speeds on level ground and slight inclines, but won’t go uphill

The Vacuum advance is new. The old one had a hole in it you could poke your finger through.
It’s the same now as it was before

Why are you running 98 octane?

To try to stop the pinging.
I’m in Australia. We have 91 or 98

The vacuum advance goes away entirely when the engine is under load- - - -uphill, passing, trailer towing, etc. The only function of vacuum advance is to get better gas mileage at light throttle cruise. As soon as the throttle is tipped open even a little, the vacuum advance goes away and all that is left is centrifugal. I've had the best results with 32-34 degrees of initial plus centrifugal advance at 2500 RPM, (crankshaft, not distributor degrees) plus another 10 or so degrees from vacuum.
Jerry

I experienced bad pinging after putting a heavy camper on my 1980 truck. Truck ran fine before the camper was installed. Filled up with fresh gas and the pinging went away. The trouble is how do you know that the gas you are buying is good?

Because I’ve been using the same stuff from the same place in my other car for years

Maybe like mine, the vehicle sits for a long time and deteriorates over time.

Australia, and most of the rest of the world use the Research Octane Number (RON) only. In the USA, we rate gas with an average of RON and MON (Motor Octane Number).

The RON ratings in Australia translate to about 4-6 higher than the API numbers in America.

Therefore, 98 octane fuel in Australia is equivalent to ~93 octane in the USA. 91 in Australia is 87 here.

Approximately a tablespoon of carbon buildup in a combustion chamber can raise the compression ratio half a point. A heavy buildup of carbon, like a little oil consumption can cause, can have a big effect on the tendency for an engine to pre-ignite the fuel, either from glowing carbon deposits that start small pockets of fuel burning before the spark plug fires, or in extreme cases, Dieseling due to compression ignition. Half a pint of very hot water, dribbled down the carburetor throat slowly with a fully warmed up engine running at a constant 2500 RPM or so can "steam clean" combustion chambers and reduce carbon deposits pretty dramatically.
Jerry

If I may, how did you determine that the mechanical advance was working properly? What is the Delco part number on your distributor? Which vacuum advance did you install, they are not all the same even though they look the same.

My 52 with the 216 did quite similar to your condition, I found the thermo flap in the manifold stuck in the closed position. Freed it up and the problem went away. That was 20 years ago and problem never has returned.

When I got it on the road about a year ago, the thermo flap was stuck open, and in Australias climate effectively boiling my fuel. Now its clamped closed and I immediately got another 10mph.
It made no difference to the pinging though. Same before and after.

Dragsix - I haven't determined that its working properly, but it is working. With the Vacuum advance, I repaired and installed the original.

Otto - thats interesting and handy to know, but I doubt it would make much difference in this case.

Jerry - I have heard of that method before. But I'm not too sure. I'd be scared of cracking the head. If carbon buildup is causing this I think I'll take the head off and clean it properly.

I've dumped many gallons of water down carburetors since 1958 when I started rebuilding engines (at age 12). Haven't damaged one yet. "Your mileage may vary", as the old adage states!
Jerry

Well then let me ask it a different way. How do you know the internal mechanical advance is working?

It looks like you are getting plenty of good advice on the timing side of it. Something Jerry said struck me though. If this only happens when you are going up hill, maybe raise the float in the carb so there's a little more fuel in the bowl. It doesn't really cost anything to try it and, if a lean condition is the culprit, you should see immediate results.

Mark

What color are your spark plugs?

Vacuum advance units vary in calibration. Some come in at 3-5 in of vacuum. At 1/2 to 3/4 throttle it could be advancing enough to cause pinging.
It would be a simple test to take a test drive with the vacuum to the dist disconnected. It might help figure out what is causing this problem.
I did tune up & drivability work on daily drivers & commercial vans for 50 years. I have found occasionally too much vacuum advance causes pinging.

George

I'm pretty sure its not the Vacuum Advance as the problem existed with a faulty VA that wasn't sucking at all. It existed with the VA removed and the vacuum line plugged. And it's still the same with the repaired VA that works.

The spark plugs are grey/white

I think the mechanical advance is working because it moves the distributor when I rev it, but I'm not sure how many degrees.

The problem exists only when the engine is struggling going uphill, so not necessarily at high revs, but while doing about 30 mph.

I haven't had time to test if it's fuel related or not. Thats the next plan.
Then I'll look at getting some of the gunk out of the combustion chambers

Combustion temperatures and potential for hot spots/detonation (pinging) increase significantly with load on the engine. As you are going up hill the load increases because the power required to move the vehicle up the hill increases, the steeper the hill the greater the load. If you run the engine speed up while standing still it takes very little throttle opening but starting moving the truck and the throttle opening to ahcieve that same engine rpm increases. Going up the hil requires even more throttle opening to achieve that engine rpm because the load is increasing. If you get to wide open throttle and cannot achieve that same engine rpm you have reached the power limitation of the engine.

Hot spots can be from combustion chamber deposits or over heated exhaust valves, generally because they are not sealing (the seal also allows heat transfer from the valve to the head). Sometimes a piece of carbon from a chamber deposit gets caught in between the exhaust valve and the seat preventing the valve from sealing resulting in a hot spot and resulting detonation.

You may be able to determine if it is fuel (octane) related by adding an octane booster but as others have said the more times you experience detonation in the process of sorting it out the greater risk of major damage to the engine.

Ok, so here is your first issue. The movement of the distributor when you rev the motor is strictly a function of the vacuum advance. The mechanical advance has no effect on the movement. It is very important that both advance systems are working properly because each has its own separate but somewhat interrelated function.

The mechanical advance is underneath the point plate so it cannot be visually inspected without taking a few things apart. There are a couple of things that can prevent the mechanical advance weights from working properly. A lot of gunk, dirt and other crud that has built up over the years preventing the weights from moving, a buildup of rust, or the weights are rusted to the pins of the mechanism preventing them from moving, broken springs or broken pins, or a combination of the above.

To inspect, you will need to remove the cap and rotor, then the black plastic insulators, retaining stud and wires (point and coil). There are three screws holding the point plate to the distributor. Two of these screws also hold the spring clips for the cap. You remove the screws and clips, then the point plate. Now the advance mechanism can be inspected. Give it a good cleaning, and lubricate the weights and springs and pins. If anything looks amiss or missing or broken, time to have the unit serviced.

In the first photo, you can see where there is a advance weight spring missing. In this instance, the spring broke from the pin, and then jammed in between the weight preventing the weight from moving outward and thus preventing the advance from working. You have to look hard, but the pointer is indicating part of the spring that broke off and fell to the bottom of the distributor, the other part got itself jammed in the weight.

The second photo is what you are aiming for. Now, you will not be able to remove the shaft from the distributor without removing the gear. So for you, I would get in there with some carb spray and clean clean clean all the grease and junk. Then a little light oil (like sewing machine oi)l, and a little dab of grease here and there, and get the advance mechanism and weights lubricated, working or working better anyhow.

Seems like you’re getting lots of good advice, but the issue hasn’t been nailed down yet. So I’ll pile on!

Shaffer's1950 raises an excellent question about color of the spark plugs: you replied Gray / White.

Wouldn’t this indicate very hot combustion chamber burning caused by excessively Lean fuel mixture? Jetting, fuel supply, manifold or carburetor mounting air leaks, and spark plug heat range are some possibilities.

Modern fuel isn't the same as fuel from 50 years ago. The spark plugs will be tan or light grey when burning normally. Go pull one from your modern daily driver and look.

The old spark plug charts we used to use to diagnose problems aren't really useful these days.

This is a current spark plug chart. Perhaps OP bajintas can pull a spark plug out of the 216 (take a pic?) and tell us what he sees.

ol 55, on that chart, my plugs look like the picture at centre top. Normal using lead replacement petrol.

Dragsix, thank you for the thorough explanation, but I've led you astray, by writing my reply in a hurry. I can tell my mechanical advance is working by looking at the flywheel. It advances way past the idling position. The Vacuum advance wasn't connected at the time.

WICruiser - thankyou also for the thorough explanation. As mentioned I'm running the highest octane fuel generally available in Australia. 98 octane, but as pointed out before that may equate to about 94 in the US.

Today, I'll test pulling the choke out as it starts to ping. Hopefully that'll help explain things.

I'm anxious to see what the cause of the problem turns out to be and what the solution is. After all, when you first posted here, you couldn't drive over 30mph. Now that those other problems have been addressed, I want to see you driving your truck.

What exactly is "lead replacement petrol"? Do the fuel companies actually add some sort of "instead o' lead" snake oil to the fuel? Nothing like that has been done here in the USA since 1974 and the predicted catastrophe has never happened. Cars that used to run on leaded gasoline didn't suddenly self destruct and the exhaust valves didn't burn.

Most people forget or never knew that AMOCO introduced its famous super unleaded "white gas" in 1923. Cars have been running unleaded for 100 years without any major issues.

My daily driver Cadillac has been running on unleaded gas for the last 23 years and 100,000+ miles.