Rate my Spark Plug

[CaptainK]

Finally found a tool that'll fit with my headers to remove the spark plugs. Pulled one to have a look.

As a complete non-expert on this, I thought I'd ask you all what the general state of the plug looked like to you. Note: I can tell the threads have oil in them, BUT no oil leaks past the plugs externally.
This is for a 1968 327 engine that has the correct VIN numbered block, but may have an unknown set of heads (still Chevy orange) on it as the standard plugs for a 1968 327 don't fit it, but later SBC plugs do. The plugs featured are NGK R - BPR5FS. I'll be replacing the plugs soon (when I order some), so don't worry - I'm just interested to see what you all think the plugs are "saying" about the engine etc. Thanks.

 

[Chuffer]

Looks like oil and carbon build up to me .

 

[CaptainK]

But does it mean anything wrong - too rich / too lean? Seals gone etc? Just thinking of related things I could do whilst changing the plugs.

I should add that the C3 has sat for about a month now un-used, in case that helps anything.

 

[antijam]

Your plug looks pretty healthy to me. Colour of the electrodes and insulator suggests good combustion. Oil fouling seems confined to the threads and quite often this happens due to valve cover gasket leaks coating the threads as the plugs are removed, although it could still be collecting from oil in the combustion chamber passing down the valve guides or up past the rings. Personally I wouldn't worry about it.
Compare your plug to this chart. If it's in the green...

 

[Roscobbc]

Kinda go along with Antijam - especially if the engine has just been started-up and not been on a run. Yes, as Chuffer says theres some carbon build-up and evidence perhaps of oil consumption.......all typical of an older engine that hasn't had a proper run. The 'real' test will be to see it all remaining 7 plugs have a similar appearance..........

 

[antijam]

While you're changing all the plugs it could be worthwhile doing a compression test - or even better, a leak-down test - to help assess the condition of the engine. A cheap but effective leak-down tester can be had for around £30.....


.... and you really need an air compressor, although it can be possible to use it with a 12V tyre inflator.
With all the plugs out you turn the engine by hand to get each piston at TDC in turn (i.e with both valves closed) and apply air pressure to the spark plug hole. The tester will tell you if the cylinder is holding pressure adequately. In the event of a low reading due to a leak, the source can usually be found by ear. A hiss from the dipstick hole indicates air is getting past the rings; from the exhaust pipe shows leakage past the exhaust valves and if from the carb it suggests the inlet vales are leaking.
Armed with this info you can make a pretty accurate assessment of your engine's condition.

 

[CaptainK]

I did ponder about doing a compression check. Don't have a compression tester, nor done one before, but thought it might be a good idea. We'll see.

I've bought the same plugs again, so I'll bung em in when I have time - no rush really. And yes, I'll no an analysis and photos of all plugs when they come out. I find it interesting. In case anyone was interested, the plug I pulled out and photoed is the one closest to the alternator on driver's side.

As mentioned above, the car is normally mostly only driven for about 5 miles at a time. Unless I'm going shopping in it for a laugh, or to a show. I am planning on going to the Corvette SW meet this weekend, so that'll be about a 70 mile run each way.

 

[antijam]

Just out of interest this is a plug I checked recently from my own 350 sbc......


Colouring is not dissimilar to yours and mine also shows oil on the threads and some carbon on the rim. I did both a compression and a leak - down test while I had the plugs out and the results suggested my engine is in pretty good condition, borne out by the fact that for a base motor on a run it goes like stink !

 

[teamzr1]

Did you mark each plug as to the cylinder plug was in to see if this one is common to what others look like
or some better looking as the others ?

That is ugly looking
Worse if not a lot of mileage on these plugs
Rich, high carbon and oil

Is the plug type too cold for the engine makeup ?

 

[teamzr1]

Compare of my 1999 C5 and 1993 Caddy Deville which its color is part due to the E10 gas where C5 uses no Ethanol at all

 

[Chuffer]

But does it mean anything wrong - too rich / too lean? Seals gone etc? Just thinking of related things I could do whilst changing the plugs.

I should add that the C3 has sat for about a month now un-used, in case that helps anything.

Sorry I didn`t reply in more detail Captain but I was just killing time until my mate turned up to go up to The Great Central Railway to work on the locos and had to sign off quick . Fortunately all the usual guys seem to have covered the issue now .