Attempt to Eliminate PreIgnition

[Charles Neuhauser]

Hi all,
My 67 Fury has a some preignition issues. It has the 318 which I assume is the LA. I have done some searching but all I could find was either change the timing (which is right where its supposed to be right now, and I also don't know how to adjust it) or run premium. I have been running premium for the past year, ever since I noticed the preignition.
I would very much like to eliminate this issue, as once the engine is to operating temp, at any load it will do it, stealing power and making me cringe. I don't want to cause any more issues than I may have already, especially with warm weather coming.
Any ideas to eliminate this issue? Different spark plugs, timing, anything? Thanks

 

[Ross Wooldridge]

There are a number of issues that may contribute to pre-ignition.

1) Spark Plug temp range. Could be too hot a plug.
2) Ignition advance curve. Static timing may be fine, but the distributor centrifugal advance and the vacuum advance (which both come into play during load conditions) may be out of whack. If they advance too far you get pre-ignition
3) Timing marks may be off - if your engine is original and you're setting your timing from the marks on the harmonic dampener, it may have moved slightly, throwing your initial settings out of whack.

The first thing to do is to see if retarding the distributor's initial setting a little helps the problem - let's say for example if your initial setting is supposed to be 12.5 degrees before TDC, set it for 10.5 before instead. If the low end and idle performance doesn't suck, then the difference may help the higher speed and advance settings.

If that doesn't help, look at the advance curve on the vacuum pot on the distributor. Some are adjustible with an allen key - turn one way lessens and turn the other increases the vacuum and how much it is applied to the mechanism in the distributor.

Inside the distributor are little springs - too light and they allow too much advance too early.

I'm just a rookie with this, but that's my basic understanding of how it works. I likely have screwed up somewhere, but others here with much more knowlege and experience will chime in and correct me!

 

[Dana]

I would first double check your timing mark, to be sure the damper has not slipped. And second, make sure that your distributor is moving properly. Sometimes they stick. Are you getting any oil into your cylinders? Does it still do it with the premium fuel?

 

[Charles Neuhauser]

There are a number of issues that may contribute to pre-ignition.

1) Spark Plug temp range. Could be too hot a plug.
2) Ignition advance curve. Static timing may be fine, but the distributor centrifugal advance and the vacuum advance (which both come into play during load conditions) may be out of whack. If they advance too far you get pre-ignition
3) Timing marks may be off - if your engine is original and you're setting your timing from the marks on the harmonic dampener, it may have moved slightly, throwing your initial settings out of whack.

The first thing to do is to see if retarding the distributor's initial setting a little helps the problem - let's say for example if your initial setting is supposed to be 12.5 degrees before TDC, set it for 10.5 before instead. If the low end and idle performance doesn't suck, then the difference may help the higher speed and advance settings.

If that doesn't help, look at the advance curve on the vacuum pot on the distributor. Some are adjustible with an allen key - turn one way lessens and turn the other increases the vacuum and how much it is applied to the mechanism in the distributor.

Inside the distributor are little springs - too light and they allow too much advance too early.

I'm just a rookie with this, but that's my basic understanding of how it works. I likely have screwed up somewhere, but others here with much more knowlege and experience will chime in and correct me!

Plugs: I was going to do plugs and wires soon, I don't really know how to tell the temperature of spark plugs. Is it written on the side? I have some autolites in it right now. I can pull them after school and check.

Ignition Advance: It does advance quite a bit at RPM, but I can't tell exactly how much because it goes off of the ruler thing on the harmonic balancer.

Timing Marks: I am setting the timing based off the harmonic pulley. It may have shifted but I have not way to tell.

I can investigate after school and come back with some more info.
Thanks a bunch!

 

[Charles Neuhauser]

I would first double check your timing mark, to be sure the damper has not slipped. And second, make sure that your distributor is moving properly. Sometimes they stick. Are you getting any oil into your cylinders? Does it still do it with the premium fuel?

How might I check to make sure it has not slipped? I can check into the dizzy later. No oil in cylinders as far as I can tell yet, oil level doesn't go down, and I can't smell any burning or see any smoke out the tail pipe. It has been doing it with the premium fuel.

 

[Charles Neuhauser]

Could this be due to the car being made to run with leaded fuel?

 

[Davea Lux]

There is a set of springs inside the distributor that control the rate of advance, if one or both of them is broken, you would be running full mechanical advance all the time. Given your timing is off the scale at idle, I suspect that might be causing your problem.

Dave

 

[Dana]

How might I check to make sure it has not slipped? I can check into the dizzy later. No oil in cylinders as far as I can tell yet, oil level doesn't go down, and I can't smell any burning or see any smoke out the tail pipe. It has been doing it with the premium fuel.

What that means is, that your number 1 piston is clear at the top of its stroke (or travel) at the same time your timing marks line up at top dead center (TDC). You'll have to take out the #1 spark plug, and if you don't have a top dead center indicator, you ca make one from an old spark plug and a 3/8 bolt rounded of so as not to damage the top of the piston. Break the porcelin off of the plug and drill it out with a 11/32 drill bit. then thread in the 3/8 x 2" bolt until it bottoms out on the old plug hex. Roll the engine over(BY HAND) so your timing marks line up. Stick a long screwdriver in the #1 plug hole, in the head. Have someone rotate the engine over (BY HAND) counterclockwise while you feel the piston go down a few inches. Screw in your TDC tool just like you would a spark plug. Rotate the engine over clock wise(BY HAND) until it hits the stop. Then mark the damper where the timing mark pointer reads zero. Then roll the engine over counterclockwise until it hits the stop. Mark the damper where the timing mark reads zero. With a flexible measuring device, measure the distance between your 2 marks. Divide the number by two and that is where the damper TDC mark should be. EXAMPLE: If the marks are 4 inches apart then you damper groove should be 2 inches, right in the middle. IF not mark a mark at exactly the middle and that is YOUR TDC.

 

[Charles Neuhauser]

There is a set of springs inside the distributor that control the rate of advance, if one or both of them is broken, you would be running full mechanical advance all the time. Given your timing is off the scale at idle, I suspect that might be causing your problem.

Dave

Sorry about that Dave, what I meant to say was at idle, its 12.5, but when rev'd up, it goes off the scale.

 

[Dana]

Could this be due to the car being made to run with leaded fuel?

Short answer: Yes it could. You've got a heavy car, small cubic inch motor probably not running at its peak, probably a very tall gear i.e. 2.76, And probably a heavy foot. Add that to a car made to run 100 octane fuel, if any thing in your distributor is off, wieghts sticking,springs broken etc. You could very well be at the point of detonation.

 

[Charles Neuhauser]

What that means is, that your number 1 piston is clear at the top of its stroke (or travel) at the same time your timing marks line up at top dead center (TDC). You'll have to take out the #1 spark plug, and if you don't have a top dead center indicator, you ca make one from an old spark plug and a 3/8 bolt rounded of so as not to damage the top of the piston. Break the porcelin off of the plug and drill it out with a 11/32 drill bit. then thread in the 3/8 x 2" bolt until it bottoms out on the old plug hex. Roll the engine over(BY HAND) so your timing marks line up. Stick a long screwdriver in the #1 plug hole, in the head. Have someone rotate the engine over (BY HAND) counterclockwise while you feel the piston go down a few inches. Screw in your TDC tool just like you would a spark plug. Rotate the engine over clock wise(BY HAND) until it hits the stop. Then mark the damper where the timing mark pointer reads zero. Then roll the engine over counterclockwise until it hits the stop. Mark the damper where the timing mark reads zero. With a flexible measuring device, measure the distance between your 2 marks. Divide the number by two and that is where the damper TDC mark should be. EXAMPLE: If the marks are 4 inches apart then you damper groove should be 2 inches, right in the middle. IF not mark a mark at exactly the middle and that is YOUR TDC.

Great info, Dana. If plugs and wires and vacuum advance doesn't work I can give it a try.

 

[Charles Neuhauser]

Short answer: Yes it could. You've got a heavy car, small cubic inch motor probably not running at its peak, probably a very tall gear i.e. 2.76, And probably a heavy foot. Add that to a car made to run 100 octane fuel, if any thing in your distributor is off, wieghts sticking,springs broken etc. You could very well be at the point of detonation.

Heavy car: Yes
Small cube motor: yes for the era
Probably not running at its peak: probably
Tall gear: the guy who does rear ends on mopars for a living estimates it is a little shorter than that, around three.
Heavy foot: Yep, but not while its being moody. I feel too bad for the engine.

Like I previously mentioned, I will try cooler plugs and new wires, and check the advance, then go into the more in depth ideas. Thanks for the insight.

 

[Charles Neuhauser]

Thanks everyone for your ideas and input, I will start with the easiest suggestions and then try the harder ones

 

[bluefury361]

I doubt its the octane if your using premium fuel. Sounds like the advance is working to, (perhaps to much advance). You might try retarding the timing 1 1/2 or 2 degrees.
How many miles on the engine? If over 70K I would replace the timing gear set with a steel cam gear.
With a timing light connected watch the timing mark at idle and just off idle. It should be steady. Fluctuation could mean a worn timing gear or dist bushing.
Good luck.

 

[bluefury361]

One other thing. Carbon buildup will increase compression and cause pre ignition.
You can dribble about a quart of water through the carb at a fast idle. That will break up carbon buildup.

 

[Ross Wooldridge]

You should know that using cooler plugs may also result in the plugs fouling up more easily - hot plugs tend to burn off the deposits that collect better than cooler plugs. It's a double edged sword. Check the distributor, check the vacuum advance and timing marks - all fairly easy to do before going to the trouble of changing out the spark plugs.

 

[saylor]

slow down guys this guy has 18 posts and says he doesnt know for sure how to set timing. all these ideas ^^ hes gonna be out there with a plunger and a jockstrap tryin to fix it.

baby steps.

try not to die -

- saylor

 

[Charles Neuhauser]

I doubt its the octane if your using premium fuel. Sounds like the advance is working to, (perhaps to much advance). You might try retarding the timing 1 1/2 or 2 degrees.
How many miles on the engine? If over 70K I would replace the timing gear set with a steel cam gear.
With a timing light connected watch the timing mark at idle and just off idle. It should be steady. Fluctuation could mean a worn timing gear or dist bushing.
Good luck.

51k on the car. Right now I think its probably too much advance. Thanks. I'll check the timing again and make sure to check if its steady and consistent.

 

[Charles Neuhauser]

One other thing. Carbon buildup will increase compression and cause pre ignition.
You can dribble about a quart of water through the carb at a fast idle. That will break up carbon buildup.

I do recall hearing about that. I'll probably try that today.

 

[Charles Neuhauser]

You should know that using cooler plugs may also result in the plugs fouling up more easily - hot plugs tend to burn off the deposits that collect better than cooler plugs. It's a double edged sword. Check the distributor, check the vacuum advance and timing marks - all fairly easy to do before going to the trouble of changing out the spark plugs.

Yeah thats true. I check dizzy and vacuum advance first. Plugs and wires are old so I am replacing them anyway though.