One oily plug - not good?

[Zebedee]

I had a slight misfire on one cylinder. After checking the plugs, 3 are a nice grey colour but the one on cylinder 1 was all oily.

Cleaned it up (and swapped it to another cylinder) and all was fine for about 1000 miles then the misfire came back.
I'm assuming the worst, worn rings on one cylinder but what else could it be?

[kevtherev]

I think it's more likely a busted ring or rings.
A squirt of oil in the cyl when a compression test is done will confirm it

[Hacksawbob]

I think oil can seep past the valves as well.

heres something I pinched from another site

Dry or wet test
Question : Can a dry or wet compression test determine valve seals leakage and worn out piston rings? If so, can it cause spark plugs to be oily or sooty?

Answer : The wet and dry test is usually done to determine piston and piston ring wear. If the valve seats are worn and there is leakage, the cylinder will not be able to hold pressure. So if you do both the wet and dry test, and the cylinder pressure is still low, you will need to check whether the seats are worn or there is a leak in the cylinder head gasket. This is done using another test, which involves putting the piston on TDC on the compression stroke and applying air pressure through the spark plug hole. Then by listening in the inlet manifold, one can tell if there is a leak in the inlet seat, etc. There are many other problems that can be detected by applying pressure this way.

Spark plugs being oily, usually indicates "blow-by" and could be wear in the pistons and rings or even worn valve guides or seals. Unfortunately it is not easy to identify valve seal leakage unless the head is taken off or if one has a scope to look at the valve through the spark plug hole. Leaking valve seals usually show as heavy deposits on the back of the valve. Sooty plugs are usually because of too rich a mixture.

[BOXY]

It might be the oil causing the misfire, but it might be the misfire making the plug look oily. If the HT lead is iffy the plug isn't sparking and getting wet with petrol. Does it smoke much? If the compression test looks ok try a new lead.

[ghost123uk]

Agree with above ^^^ = get a reliable garage to do a compression test on it.


Does it make any smoke at any time during starting or driving ?
Does it need oil top ups ?

[Zebedee]

Theres no smoke at all.
Will probably replace the leads and see.

Never thought to check if it was petrol or oil on the plug. It was wet and shiney so assumed oil.

[kevtherev]

Ah we have not been

Never thought to check if it was petrol or oil on the plug.

Gah!

[Zebedee]

Its definately oil.

Now having problems starting on LPG. Feels like its flooded, tries to catch and fire but doesn't.
Time to renew the plugs and leads i think.

[ghost123uk]

Its definately oil.

Now having problems starting on LPG. Feels like its flooded, tries to catch and fire but doesn't.
Time to renew the plugs and leads i think.

If it is Oil then renewing the leads and plugs ain't going to help much though is it

[Zebedee]

I'm just confused now.
It seems it was just a load of oil on the threads which appears to have dripped from a small hole in the bottom of the airfilter housing. Why theres oil in that i don't know. Its not much maybe 1/2 a tea spoon full.
The plug is clean and a nice biscuity colour now.

I also found that one plug lead (to number 1) was a loose fit in the dizzy cap.

[kevtherev]

crank breather dumps oil mist into the air duct.. some of it condenses and runs out

Perhaps you could fully investigate first before asking questions and getting misleading answers?

[Zebedee]

That would have probably made more sense.

[ghost123uk]

Well this is good news Zebedee

At least it means you don't have an immediate and big problem.

[Zebedee]

True