Pre Ignition and Detonation / Pinging / Pinking / Knocking

addo

Contented Peugeot Driver
I thought Roger's comments deserved better than being buried in a post that many might gloss over on their search for meaning:
lhs2.1 said:
think some clarification is needed.
Firstly, as far as I'm aware there is no combustion phenomena known as "pre-detonation".
For a gasoline fuelled IC engine there are two separate abnormal combustion processes, which are separate but can be interlinked. These are "pre-ignition" and "detonation". The latter is also known as "knocking" or "pinging" or "pinking".
Pre-ignition is when ignition of the fuel-air mixture in the cylinder occurs before the spark plug event. This ignition can be initiated by a incorrect heat-range spark plug, or incandescant hot-spots in the combustion chamber.
Detonation is when there is spontaneous combustion of the the fuel-air mixture in the combustion chamber ahead of the flame front progressing from the spark plug ignition. When this happens there is a rapid rise in local pressure causing a shock wave in the combustion chamber which may be heard as a knocking sound.
Detonation can result from too much ignition advance. too low an octane rating of the fuel, too high a compression ratio, and from pre-ignition. It is influenced by manifold pressure ie engine load, and if detonation is allowed to persist, the shock waves can damage piston crowns and ring lands.
For the engines we're discussing here, pre-ignition shouldn't be a problem assuming that correct spark plugs are used, and that there haven't been running problems in the past which may have resulted in excessive deposits in the combustion chambers.
Octane ratings of gasolines are really indicators of the detonation resistance of the fuel. Even the un-leaded 91 octane crap that we are served up today is far superior (in detonation resistance) to the fuels available when the Dees were launched. Consequently, there is scope to advance the ignition timing beyond the original OEM recommendation.
However, setting the optimum ignition setting is a trial and error process and relies on the ability of the operator to hear when detonation is happening ie when to back off the advance. Some people are good at hearing "pinking", others aren't.
My advice is to set the static ignition timing to the manufacturer's recommendation, find a nice clear road, roll at 60/70 km/hr and floor the accelerator in a high gear and listen for a tinkeling sound. If no sound, tweak the ignition advance and repeat until you hear it. Then back off the static timing a degree or so.
In a previous life I spent some years testing fuel octane requirements of cars, including verification of this for pre-production for most of the major Oz manufacturers.
roger
Nothing to add myself other than opinion. :wink2:
 

Alain

New member

Pinging problems

If pinging persists after a distributor timing adjustment (with a timing light)and the fuel quality is known it is usually a mechanical issue most likely being the distributor itself.
As an example i purchased a Renault R20 years ago in WA with an inheritant ping. The seller (mechanic) said that the head had been skimmed quite a bit and that was how it is. Knowing the quality of WA water and the reluctance of some owners to service correctly that was plausible and i put up with it for some time.
Eventually pissed off with this, i pulled out the dissy to find one of the counter weight springs disconnected.
Needless to say the Renault was totally restored power and driveability wise.
A new or low wear (low mileage) dissy totally transforms older pre electronic vehicles and should be the first place to look when chasing performance and driveability issues with on road fine tuning to fuel to follow.

Alain
 

JohnW

Too many posts!
Which is precisely why I bought a 123 distributor for the CX (carbie type) and have a Hall Effect device in a near new distributor in the R8. I totally agree about getting the distributor really right first, in other words. I was talking recently to a guy with many years experience with Strombergs in his business and he reckoned that 95% of complaints went away when owners took their advice to fix the spark first and then come back to fix the carbie.

I have found with the 123 in our CX that the onset of pinking is quite sudden as the static advance is changed. Rotate it a mm or two in the advance direction and it goes from no pinking to noticeable pinking (front window down) on the hill up to our house.

Reading the excellent article (Thanks Jo) it seems I have never heard pre-ignition and what I am hearing as a tinkling noise is actually detonation. Very interesting topic.
 

tobytronic

New member
@lhs2.1
"It is influenced by manifold pressure ie engine load, and if detonation is allowed to persist, the shock waves can damage piston crowns and ring lands."

Simply put, I've read about this sort of stuff almost every day since 1974. Yes, I am sad, but don't care. One bit.
So, yes, a superb post. It wasn't until 2007 that I started to understand the MPA's role in 'pinking'. Please write some more. Thank you.
I've just realised that I have resurrected an old post? Sorry, I'm new...
 

RINGER

Member
http://www.aussiefrogs.com/forum/re...t-all-ducellier-distributors.html#post1610700

Check this out near the end.
I time all older carburetor vehicles with a vacuum gauge for great near perfect timing results when using modern day fuels.

Mechanics trained @ Carlisle TAFE College W.A. in the 1970's & probably years prior to then, were taught engine tuning & diagnosis using these inexpensive very handy tools.

Give it a go! Don't use any vacuum advance port unless it is full manifold vacuum & they usually are not.
 

RINGER

Member
The above link didn't seem to work but this one should:
The timing with a vacuum gauge is right near the end
 

alina007

New member
Which is precisely why I bought a 123 distributor for the CX (carbie type) and have a Hall Effect device in a near new distributor in the R8. I totally agree about getting the distributor really right first, in other words. I was talking recently to a guy with many years experience with Strombergs in his business and he reckoned that 95% of complaints went away when owners took their advice to fix the spark first and then come back to fix the carbie.

I have found with the 123 in our CX that the onset of pinking is quite sudden as the static advance is changed. Rotate it a mm or two in the advance direction and it goes from no pinking to noticeable pinking (front window down) on the hill up to our house.

Reading the excellent article (Thanks Jo) it seems I have never heard pre-ignition and what I am hearing as a tinkling noise is actually detonation. Very interesting topic.
i also want to buy it please give me suggestion
 

RINGER

Member
The guy you spoke to is telling you exactly what any old time mechanic would ~ that is over 90% of thought to be fuel problems turn out to be electrical/ignition. That is why, unless one is certain fuel is the issue, that the ignition must be eliminated & that will usually take <5 minutes.

Pre-ignition & detonation are not the same thing.
Pre-ignition is as the name says. It happens when the fuel air mixture is ignited before the spark occurs.
Detonation/pinging/pinking, that most are concerned about, is generally associated with the spark occurring @ the wrong time.
The sound one hears is usually like someone shaking marbles in a tin can on acceleration UNDER LOAD.

Summit ~ What causes it?
Detonation can be caused by several factors. A few common causes are:

Over-Advanced Ignition Timing
If Ignition Timing is too far advanced, the spark plug fires too soon. This causes the flame to end early. The remaining fuel can detonate.

Lean Air/Fuel Mixture
A rich Air/Fuel Mixture runs cooler than a lean mixture. A lean mixture can get too hot and detonate.

Too Much Compression
Compression causes heat. If the air/fuel mixture is compressed too much, it can detonate.

Engine Overheating
Low coolant or a bad water pump can cause the engine to overheat. Too much heat can cause the air/fuel in the chamber to detonate.

Low Octane Fuel
Octane Rating is a measure of "knock resistance". Switching to higher grade fuel can help a knocking engine.
 
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JohnW

Too many posts!
i also want to buy it please give me suggestion
I bought mine from https://www.123ignition-conversions.com/ because the 123 Ignition folk didn't offer a Citroen CX distributor back then. I sent them a spare distributor and they fitted the 123 unit. I've recently done the same with my Renault R8 ignition system. Very good service and, being Dutch, they speak good English. :) Easy to fit of course and it has an LED that allows you to set the static timing easily.
 

RINGER

Member
I will add over advance to some may appear like diesel knock or even tappet adjustment to others.
In petrol engines this 'signal' has damaging consequences. JG
 

Cookiemonster

New member
Hi, just bought a '79 504 TI with 200,000 miles on it. "pinks" under load, especially on 95 Octane, less on 98 Octane. Have advanced the timing a little bit too. Question really is this: should I try 100 Octane (local station has best price in town)
 

RINGER

Member
The timing should be retarded not advanced further to reduce pinging.
Higher octane will reduce pinging over lower octane rated fuels.
 
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COL

Alpine A110
Hi, just bought a '79 504 TI with 200,000 miles on it. "pinks" under load, especially on 95 Octane, less on 98 Octane. Have advanced the timing a little bit too. Question really is this: should I try 100 Octane (local station has best price in town)

It should be able to run on 95 octane. Maybe there is something wrong with the distributor advance system, could be worn pivots or a broken spring. If its pinging you should be retarding the ignition that is turn the distributor the same direction as rotation of the rotor button.
 

Cookiemonster

New member
It should be able to run on 95 octane. Maybe there is something wrong with the distributor advance system, could be worn pivots or a broken spring. If its pinging you should be retarding the ignition that is turn the distributor the same direction as rotation of the rotor button.
Hi, yes - my mistake, I did Retard it, not advance it.
 

schlitzaugen

1000+ Posts
Did you take any measurements before and after to see where the ignition is/was? Asking because as Col said, your ignition may be off due to wear and you might be chasing your tail.

Also, being an old car, I would look at its general state before trying this or that. For all we know your combustion chamber might be full of carbon deposits, which have the bad habit of glowing red and initiating ignition before the spark plug fires.
 
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