Fiesta oily plug? Oil rings needed?

Fiesta 1100 K reg with about 85000 on the clock.
A friends car was missing and after investigation I found one plug not firing. I removed this and replaced with a new plug.
I found that the plug I removed had accumulated some oil and this was stopping it firing.
The car then seemed to run fine. After about a week and 300 miles the car was again missing on the same plug. I noticed that there was oil around the plug hole above the plug. The engine did seem a bit oily and again the plug I removed had a certain amount of oil stopping it from firing.
I checked the rocker cover nuts and these were barely hand tight. The missing plug is the one near the gearbox end under the filler cap. I therefore tightened all the rocker cover nuts.
My question is could oil be running down the engine and into the spark plug hole and then down the threads of the plug finally causing the plug to fail to fire or is it more likely that there is an oil ring problem on the piston. Could the piston be pushing oil up past the spark plug? Incidently the engine was low on oil, on it's previous visit I had topped it up so I estimate it used about 1-2 pints in 300 miles. The exhaust however shows no great oily smoke.
Having done a large mileage in another fiesta I know these engines are virtually indestructable I'm reluctant to think it is the oil ring on the piston. I'm waiting to see how the car is after a further week or so.
Any suggestions here please? Would an oil ring change be a relatively quick job or is it major engine dismantle?
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On Mon, 22 Dec 2003 19:12:03 +0000, David Cawkwell wrote:

Virtually no chance of that happening.There is the remote chance of the inlet valve and valve seal on that cylinder being worn, but unlikely to show so much oil on the plug.

More than likely to be bore wear.Either bore wear or ring failure, either will be expensive and time consuming to do.If one bore has worn, the others are likely to be on the way out too.Doing it yourself will likely cost close to 200 for just replacing the rings, as well as the hassle of removing the engine.If the bores are worn, scrap the engine, and get another from a breakers.

Major job - gearbox off,engine out, strip the head off, strip the bottom end out, then hope the bores arent worn. Alan.
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Or you could just fit 1 grade hotter plugs & hope they burn the oil off.
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A friend of mine bought a 1984 bmw 520i ... which was smoky from the day he got it with 22000 miles on it. At 92000 miles (and many, many litres of oil) the head gasket failed. Upon rebuild of the head, i discovered number 2 inlets' valve stem oil seal to be damaged ... obviously from the factory. The car is at 187000 miles now, and doesn't use any oil between changes.
One other thing .... the inlet port on the dodgy cylinder had a huge amount of carbon constriction ... leaving a mere 3cm hole down the middle.

Do fords still suffer from steps at the top of the bores?? E.G: Mega bore wear.
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Is it not possible to just take the head and sump off. I did a fiesta once in this way and job done. But for a mechanic to just do the sump and piston ring replacement it was around 120. I took the head off myself.
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On Tue, 23 Dec 2003 00:32:26 -0000, John Woodhall

Yes but it's normally quicker to take the engine out
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Ok.
What's the best way to verify that it is an oil ring that is giving the problem?
I assume I should take a compression test and compare to the other cylinders. Then drop a little oil down the cylinder and see if the compression increases. What sort of compression should I be expecting for a healthy oil ring and piston.

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On Tue, 23 Dec 2003 20:10:18 -0000, David Cawkwell

Tis in the Haynes Manual but at least 7 PSI. What's more relevant is there shouldn't be much difference between cylinders Then decide whether or not it's worth fixing.
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I'd certainly hope to see at least 7psi from any engine that was still running :)
Dave Baker - Puma Race Engines (www.pumaracing.co.uk) I'm not at all sure why women like men. We're argumentative, childish, unsociable and extremely unappealing naked. I'm quite grateful they do though.
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Fair point, bar ,psi wot's the difference again? Yeah I'm always surprised quite how low the worn engine limit is.
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I don't think there is any simple way.

The compression has little effect on oil consumption - it's not unusual to have good compression on an engine that burns oil - or even the other way round.
The oil control ring(s) is different in design from the compression ones.
You could eliminate valve seal problems first, though, as this is easier than removing pistons. If, with the head off, there is an appreciable 'lip' (finger nail thickness or more) at the top of the bores then the chances are it's re-bore time.
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