Aaron,
I think Phil might be a little pessimistic in his appraisal. It is just as
likely that a bit of grit or carbon has built up or stuck behind the valve.
If you do a compression check (the first step), do it dry first. Then squirt
a couple of teaspoons of engine oil and repeat the test. If there is no
significant change in the pressure, you likely have confirmed a valve
problem. If the pressure does go up, that indicates a ring problem. Since
the pressure was at about 120 PSI before the problem, you will likely see
some increase in readings wet, but that should be reflected in the other
cylinders as well.
A head off is required in either case, so have a good look-see. My bet is
that you will find something stuck under the valve. Certainly Phil is
correct in that it is easier to do an engine job once instead of twice, but
my philosophy has been that if it works, don't fix it. When you are prepared
to do the total overhaul both physically and financially, then do it. Until
then 120 PSI will still allow the engine to perform reasonably well.
Cheers,
Lew Palmer
-----Original Message-----
From: owner-mgs@autox.team.net [mailto:owner-mgs@autox.team.net] On Behalf
Of Aaron Whiteman
Sent: Tuesday, January 06, 2004 1:04 PM
To: jello@ida.net
Cc: MG Mailing List
Subject: Re: head advice needed
On Jan 6, 2004, at 10:29 AM, jello@ida.net wrote:
> It sounds like you have a bent valve, or a dropped seat if the valve
> won't
> close.
Whoops, missed some points. When I say the valve doesn't close, I mean
that it doesn't completely close. It does operate. I turned the head
over, the valve looked pretty close to closed, I poured water in the
chamber, and it drained out the exhaust port (and/or froze).
Another note: This was right sudden. I drove home from the airport on
Friday (the car was buried in snow, had been sitting there since the
24th) without problems. Drove for food Friday night without problems.
Sunday morning, I could hear the lack of compression when the starter
turned the motor over.
> Be sure to look at the top of the piston
> to see if there is damage or not.
There is no piston damage, nor any damage on the piston wall (I was
also concerned about broken compression rings).
> Heads with hardened seats last quite a
> while - the big thing to check for is usually a crack between the two
> valves or the valves and the spark plug. IF all else is good, and the
> other valves are seating ok and everything, I'd only replace the one
> that
> is effected.
Will do. I haven't started checking for cracks yet, since my hands
were starting to stick to metal. I hope to be able to take the head to
a heated shop tonight to look things over more carefully. With any
luck, I will find the tools I need there too.
> I think that the compression pressure should be more like the 144 range
> though - but I'm used to a higer compression earlier engine, and that
> may
> be a little off.
I dunno what it should be, but 120 lbs is decent enough pressure.
Given that I live at 2500 ft, atmospheric pressure should be about 13.5
lbs/inch, so 120 lbs is something around 8.9:1 compression (to be
accurate, I needed to know atmospheric pressure when I took the
readings).
> With the head off, you've got it half apart already, I'd consider my
> finances, and if I could, I'd just do the rebuild now rather than wait
> 30,000 more miles.
Right now, it's either rebuild the motor, or body work. Since the
engine works well, and doesn't leak, I would rather concentrate on the
body and paint unless I discover lots of damage. Additionally, it is
the middle of winter, and I am working outside. I will rebuild if I
have to, but not by choice!
> I'd also consider (since you already have a head
> without air ports) going to an earlier specification on the engine
> specs -
> slightly higher compression, and dual carbs like a '67 or earlier
> engine.
That is my eventual goal. I've already converted to the HIF carbs, and
plan to tune accordingly. Then again, I might just go for
lower-compression and convert to a supercharger. It's all long-term
right now ;)
--
Aaron Whiteman -- http://www.wsu.edu/~aaronpw/MG/
'75 B (red for now), HIF4 carbs
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