Compression test results and a couple questions..

[jimlj66]

I put in some new spark plugs today, and while I had them out I did a compression test.
1. 150
2. 145
3. 145
4. 146
5. 150
6. 145
I think this is good isn't it? This was done on a cold engine at 6,800' elevation.

When I put the plugs back in, I could tell I had a miss so I pulled spark plug wires 1 at a time till I found #6 was not firing. I put one of the old plugs back in and all was well. The new plug I had put in #6 had a light covering of oil on it. (I didn't use any oil when I did the compression test) Any idea where the oil would have come from? Bad valve guides? (wouldn't bad guides let the valves move around and effect compression?) Bad valve seals?

The old plugs all looked about the same, light gray ash deposits on the porcelain, black on the electrode. Are the ash deposits burned oil? I have a '82 large log head sitting on the shelf that has plugs like I'd expect to see, dark brown porcelain and black electrode.

 

[Frankenstang]

Yeah, those numbers look good

When I put the plugs back in, I could tell I had a miss so I pulled spark plug wires 1 at a time till I found #6 was not firing. I put one of the old plugs back in and all was well. The new plug I had put in #6 had a light covering of oil on it. (I didn't use any oil when I did the compression test) Any idea where the oil would have come from? Bad valve guides? (wouldn't bad guides let the valves move around and effect compression?) Bad valve seals?

Oil on plug likely a byproduct of this miss. My guess a lack of combustion heat leaving the rings a bit less seated while running and nothing to burn off blowby reaching the combustion chamber on non-firing cylidner. Don't think it's anything serious beyond that with those compression numbers and the fact you've resolved the miss. Good thing you tracked it down.

EDIT: PS You could always re-check #6 after some run time.

 

[rbohm]

8) your compression numbers are excellent. as to your miss, it sounds like you got a bad plug, and the oil on the plug is a result of the miss. the ford six uses a hotter plug than the V8s do because of oiling issues the six tends to have over the V8. light oil deposits are nothing to worry about.