Ladies and Gentlemen:
I haven't had much to post lately as my spare moments have been filled with
unscheduled service work to the fleet. My good ol' MGB-GT insisted on a
complete brake job by seizing a caliper. Both calipers were in pretty bad
order, so I purchased rebuilts from a well-known hydraulics shop. As usual,
their service was fast and the hardware impeccable.
The other unplanned job was a toasted exhaust valve on the MGA roadster.
I've owned this rig for the past three years, but have only been driving it
this year. Some of you might remember its taillights (OK, its headlamps,
too) from the 1000 mile Missouri Enduro last spring. It is a very early
mkII with a checkered past. The engine is a non-original +.030" 1600 with a
mkII head. When the compression in No. 4 dropped to 60 psi it was past time
for some attention. Strangely, it still performed pretty well, with just
that slight fluttering exhaust action indicative of a burnt valve.
When I pulled the head, I found part of the answer to why this engine
performs so well. It easily outruns the MGB and is the strongest "A" I've
driven. The pistons are of the flat-top high compression variety, and
someone has ported and polished the head extensively if not expensively.
The combustion chambers have also been contoured and smoothed. Naturally,
my palms began sweating as I hustled it off to the machine shop for
magnafluxing and inspection. The machinist deemed it fit to use and since
its history is unknown I assumed that the head had been milled in the past.
I asked him to check it for flatness and to only remove the least amount of
material if planing were necessary.
Now I have it back and am concerned that it may be excessively milled by
the cumulative amount of machining it has had over the years. I have some
spare "B" series heads about and have measured the head thicknesses as
follows:
MGA 1500/1600 = 3.180" (80.8mm), from a 1500, history unknown.
MGA mkII = 3.170" (80.5mm), history unknown.
MGB 1800 = 3.150" (80mm), from '63 model, history unknown.
The head I am trying to use measures: 3.075" (78.1mm).
The MGB special tuning manual indicates factory spec at 3.170" + or - .015".
All measurements are from machined face to machined gasket surface (where
valve cover gasket rests).
I do not have the burette setup to accurately measure the combustion
chambers, but I may have to devise one in order to answer my questions.
Does anyone know the factory dimensions for head height? I am probably
milled at least .095" (2.4mm) from stock. Is this excessive? Should I
consider double-gasketing the head? Will I be able to burn 92 octane fuel?
I will appreciate any answers or speculation on this problem. Thanks.
David F. Darby
Hercules Wilderness, Missouri, USA
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