Grey Deposits on Spark plugs

[fgc]

Hi,

Pulled my plugs and discovered that 2 and 3 have this grey deposits on both the centre ceramic and some on the bendy electrodes. Any idea what that means? These greyish deposits can be scraped off quite easily to reveal the bottom which seems undamaged.

Unfortunately I do not have a digital camera otherwise will take a photo of it.

Thanks.
fgc

[papajam]

Sounds like ash deposits from additives in the fuel and/or oil. You might try switching fuel brands but since the deposits are in cyls 2 & 3 only, I don't think it would help much. Cyls 2 & 3 are probably starting to push a little oil. What weight/brand oil are you using?

[fgc]

Hey Papajam,

Thanks for the insight.

I'm using 20-50 mineral oil. I live in the tropics wondering if it will help if I go straight to a 40w oil?

Just wondering... I think I had cleanish plugs until recently where I started playing with plugs and tuning of the carbs ... ... just wondering if running lean etc would give the same effect?

I did notice that everytime I take the plugs out, the plug threads would have traces of engine oil but the plugs themselves are not oily.

Any idea how to tell if its the valves or the rings that is letting the oil through?

Thanks again
fgc

[papajam]

I've been using 20W-50 decades as have many others and it works very well so I see no reason to change to straight 40. My initial thought was that there was 10W-30 or something thin like that in the engine.

If you're running leaner now, and the deposits are from the fuel, I'd think that there would less deposits. And you would see them on all 4 plugs. That's why I think that cyls 2 & 3 are burning a little oil.

There's no way that I know of to determine whether it's valves or oil rings that's passing oil. A compression test doesn't test the oil rings, just the compression rings and how well the valves are seating.

On the other hand, a little ash deposit on the plugs won't hurt anything unless there's so much of it that the plug starts to misfire. How many miles does it take for the deposits to form? And how much oil does the engine use?