Technical 1 foul plug

[StefP0342]

Hi,

See attached the picture of the spark plugs. Spark plug to the front of the car has black deposits, while the plug towards the rear of the car looks normal (i suppose). Car runs well, to be sure i let it be inspected by a mechanic. He told me nothing is wrong with the car. Considering there is just 1 air/fuel intake, it can’t be a fuel mixture that is too rich, right?

Curious for your opinion, thanks!

 

[Goldnrust]

You are right in saying that, with the single carb and shared intake port, it’s unlikely to be a mixture issue cause the difference.

Ultimately I’ve seen much worse fouled plugs, so I’d not be too concerned.

It seems likely to me that one cylinder is burning a little more oil than the other, via worn valve guides or piston rings, but as I said it doesn’t look ‘bad’ so I wouldn’t over worry right now.

Alternatively if one of the plug leads, one contact in the distributer or one of the spark plugs is bad then an uneven spark equality could cause an uneven burning of the fuel? You can always test and inspect the these parts but I don’t think I’d the most likely option.

Finally if one of the valves isn’t sealing right, that could cause an uneven burn in the cylinder and account for the difference. Could do a compression test and check valve clearances if you wanted.

I think one cylinder just burning a bit more oil than the other is most likely cause though.

 

[bugsymike]

My thoughts are it looks more like soot than oil deposits.
If it wipes off easily onto your finger then soot, oil tends to stick more to the plug and make more of a deposit on the insulator of the centre electrode.
Assuming the plug inspection was following a good long road test so engine fully warmed up, not just down to the shops, then generally both plugs should look the same.
Both plugs same heat code etc.?
Another test you could do is using an Ohm meter measure resistance, comparing both from HT lead at distributor to the tip of the centre electrode, if one is higher it causes the plug to breakdown under load earlier.
The problem is more common these days with resistor plugs and carbon HT leads for radio suppression.
I found many years ago using a Champion Spark plug cleaner and tester at a garage where I was foreman, that two brand new spark plugs , same make and heat range, but one a resistor type, that as you turned up the air pressure when testing, the resistor one failed/started to misfire first.
Consequently if there was an option I would always fit non resistor plugs for reliability and preferred copper core HT leads to carbon string type. If I had a misfire on a car under load I often tested the HT leads for continuity using an Ohm meter, all carbon leads have a resistance and the longer the lead the higher it is. However if no continuity it indicated a internal break in the carbon string usually caused by a mechanic yanking on the lead to pull plug cap off rather than pulling on the cap.
The result would be the engine would start and run fine as the HT spark would jump that gap, but when under load or in damp conditions it would fail.
In the old days coil voltage supplied to the spark plug was often only 5KV where as now 30KV or more is standard, this encourage a misfire when under load or damp weather.
Some years ago one of my sister had a Honda she bought new and always had dealer serviced, several times she complained about a misfire and as a result they fitted expensive new ignition coils which would work for a few thousand miles then the fault reoccurred. She mentioned it to me and I asked her about spark plugs, she spoke to Dealership who said they were special long life type which were not due to be changed at those services. I told her to tell them to fit new spark plugs and the problem was cured, however she was down the cost of several sets of coils at over £200 a time!

 

[StefP0342]

Resistences are equal, and I can’t wipe the deposits off, so it does appear to be oil. Although the car doesn’t really use up a noticable amount of oil. This is buildup of a couple of thousand kms over a few months, so i suppose the degree of poor valve or pistonringseal is limited?

 

[bugsymike]

Resistences are equal, and I can’t wipe the deposits off, so it does appear to be oil. Although the car doesn’t really use up a noticable amount of oil. This is buildup of a couple of thousand kms over a few months, so i suppose the degree of poor valve or pistonringseal is limited?

You didn't mention at what point the plugs were inspected?
If vehicle is only used for local low speed journeys you may help it by going up one heat code on the spark plugs.
What this means is the higher the heat code the more the electrode is extended into the combustion chamber so runs warmer and self cleans better.
However the warning is if you decide to do full throttle long distance runs, in extreme cases it can cause plugs to overheat and burn holes in pistons
Generally one code number up or down is not excessive.In the old days if a customer had a car with a worn/oil burning engine that fouled plugs regularly I would advise them to go to a "hotter" plug if they didn't want to have engine repaired.

I used to have the NGK charts and recommended plugs for most common vehicles, but this is from online.

"Typically the heat range for NGK Spark Plugs varies from 2-11. This number indicates the thermal characteristics of a spark plug, or how 'hot' or 'cold' a spark plug is. The term hot/cold is commonly used to describe whether a spark plug heats up easily (hot) or whether it provides resistance to heating up (cold)."

 

[StefP0342]

You didn't mention at what point the plugs were inspected?
If vehicle is only used for local low speed journeys you may help it by going up one heat code on the spark plugs.
What this means is the higher the heat code the more the electrode is extended into the combustion chamber so runs warmer and self cleans better.
However the warning is if you decide to do full throttle long distance runs, in extreme cases it can cause plugs to overheat and burn holes in pistons
Generally one code number up or down is not excessive.In the old days if a customer had a car with a worn/oil burning engine that fouled plugs regularly I would advise them to go to a "hotter" plug if they didn't want to have engine repaired.

I used to have the NGK charts and recommended plugs for most common vehicles, but this is from online.

"Typically the heat range for NGK Spark Plugs varies from 2-11. This number indicates the thermal characteristics of a spark plug, or how 'hot' or 'cold' a spark plug is. The term hot/cold is commonly used to describe whether a spark plug heats up easily (hot) or whether it provides resistance to heating up (cold)."

I put the plugs on the picture in the car in August of last year I think. Then after some ignition issues last week I replaced the condensator and readjusted the points, which did the trick. However, when reconnecting the HTleads, the connecting part of spark plug 1 remained in the HTlead and caused the engine to fire on 1 cilinder so I replaced the plugs and noticed the deposit on one plug. Since then i have driven 100 km with no issues
As for my driving habits: I drive the car quite regularly, +-50km at a time and like to put my foot in it so to say so i don’t think i need plugs with a higher heat rating

 

[bugsymike]

I put the plugs on the picture in the car in August of last year I think. Then after some ignition issues last week I replaced the condensator and readjusted the points, which did the trick. However, when reconnecting the HTleads, the connecting part of spark plug 1 remained in the HTlead and caused the engine to fire on 1 cilinder so I replaced the plugs and noticed the deposit on one plug. Since then i have driven 100 km with no issues
As for my driving habits: I drive the car quite regularly, +-50km at a time and like to put my foot in it so to say so i don’t think i need plugs with a higher heat rating

So hopefully just the end of the plug stuck in plug cap.

 

[StefP0342]

So hopefully just the end of the plug stuck in plug cap.

Yes only the last connecting part came off as marked in the picture. I did not know that was possible so perhaps i was too careless when removing the leads

 

[bugsymike]

Yes only the last connecting part came off as marked in the picture. I did not know that was possible so perhaps i was too careless when removing the leads

Some plugs come with non detachable terminals , some that screw on were to suit different engine/applications.
Where they do I used to tighten when fitting to customers vehicles with a pair of pliers as they are known to unscrew.
Now retired all my vehicles are diesel

 

[the hobbler]

Loo

Some plugs come with non detachable terminals , some that screw on were to suit different engine/applications.
Where they do I used to tighten when fitting to customers vehicles with a pair of pliers as they are known to unscrew.
Now retired all my vehicles are diesel

Looking at the pictures of your plugs, the 'fouled' plug seems to have more deposit on the thread. Is it possible that plug wasn't tightened up correctly and you had slight 'blow-by'? I use NGK plugs---BP6HS. If I need to go a bit 'hotter', I go up to a BP7HS---the engine definately runs a bot 'leaner' with the '7's.

 

[StefP0342]

Hi, just to come back to this issue:
Last week i drove the car 100 km+, no issues or noises to report. Parked the car, and when i started it after it cooled, a rather nasty knocking noise started with each rev of the engine. Couldn’t hear where it came from, so I used a stethoscope to try to locate it but didn’t really manage… the noise is definately the loudest & clearest near the valvecover, so I assume it is valve gear related. Adjusting clearances didn’t work. For some reason the intake valves had way smaller clearances than the exhaust valves. Do you know what could cause this, apart from me possibly adjusting them poorly last time?
Also: if the crank or camshaft or related bearings were poor, would that be easily identifyable with the stethoscope? I’ll bring the car to the shop nonetheless (again….), but it is just for my own information.