It sounds like you have a bent valve, or a dropped seat if the valve won't
close. Usually the problem is more likely to be a burned valve, but those
close, they just don't seal up. Be sure to look at the top of the piston
to see if there is damage or not. 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.
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.
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. 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.
Phil Bates
'67 MGB
'58 MGA
Misc other european cars
> In the 3 degree heat last Sunday, I discovered that I have no
> compression in my #2 cylinder.
>
> I have the original 1975 18V block, with an earlier head. I have no
> idea what specific year the head is for, but it lacks air injection
> ports. The previous owner told me that the engine was rebuilt with
> valves and seats that were compatible with unleaded fuel.
>
> I pulled the head last night (it was warmer yesterday, highs around
> 20), and my problem is the exhaust valve is not closing. I hope to be
> able to pull it out tonight and look at it, but I have to come up with
> the tools to do so before I can. If the valve is damaged, is it false
> economy to just replace the one, or should I look at all 8 before
> putting everything back together.
>
> The engine is starting to show some signs of wear (but no leaks yet),
> so I plan on rebuilding everything in another 30000 miles anyway.
> Until Sunday, the car ran perfectly, with 120 lbs of pressure in all
> cylinders.
>
> Also, a special word of thanks to all those that participated in a
> "block heater" thread around 1999, I will be installing one of those
> too, based on the advice I read there.
>
> --
> Aaron Whiteman -- http://www.wsu.edu/~aaronpw/MG/
> '75 B (red for now), almost mostly
working
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