Dunno about an MGA (although it is unlikely to be different) but on the B
hardened inserts are used for the seats as well as special valves,
originally the seats were part of the main head casting (but you probably
already know that :o).
On the one hand I'd just replace the one valve and lap it in. But on the
other a significant amount of protection against valve seat recession from
use of unleaded comes from the years and 10s of thousands of miles of use of
leaded fuel beforehand, leaching into the seats and valves. By just
replacing a valve the seat will still be protected unless it is *recut*, but
the valve won't be. But then the problem of using unleaded has always been
described as valve *seat* recession in my experience, i.e bits of material
being transferred from seat to valve from micro-welding, and then probably
burnt off the valve. In which case a new valve may well still be OK. There
is also the usage to consider - whereas long journeys at motorway speeds of
70 or so are likely to cause a problem on an unprotected engine, lower speed
touring much less so. There are also additives to protect against VSR, I
use Castrol's in my roadster (the V8 was built with hardened seats anyway
being alloy headed).
All-in-all I think I'd just replace the single valve, see how it went, and
if it had problems of recession only then convert the head and valves to
unleaded. The less unnecessary work you do the less the chance of a
knock-on problem.
PaulH.
----- Original Message -----
> On an MG note I am about to have the head pulled off my MGA due to a bad
> valve. I wonder if I should just replace all of them and if so what is
> the
> best choice for seats and valves? I understand there are seats and valves
> that are produced to accept unleaded gas.
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