Valves, rings, holed piston can all cause a single cylinder to be down. A
head gasket is more likely to fail between 2 and 3 and hence cause two low
readings. If the gasket has blown anywhere else I would expect to see
symptoms in the oil, water, or round the head/block join. Retesting the
compressions with a teaspoonful of oil in each can differentiate between
valves/pistons and rings, the former will cause no significant increase in
the reading but the latter will. Also listening to the exhaust, intake and
oil filler can reveal which valve is leaking, or rings.
----- Original Message -----
From: "Tony Sheehan" <multitech@cairns.net.au>
To: "MG genius list" <mgs@autox.team.net>
Sent: Friday, August 30, 2002 9:25 AM
Subject: RE: Running roughly and blowing blue smoke....
> Ok, I've had a chance to take out the sparking plugs and perform a
> compression test. Plugs from cylinder 1 & 2 looked normal, 3 & 4 looked a
> little oily (but not badly). Cylinder 2 pressure tested to around 60psi,
> all the others tested to 155ish.
>
> I'm thinking a head gasket, or does that always mean water in the oil? (of
> which there is none). Can dodgy valves cause pressure drops?
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