In 30 years of owning and driving my Morgan +4 it has rarely had an air
filter on it, but has usually had one available should the need arise. Most
of the time, in urban California at least, there has been no need to use an
air filter. But I have experienced 3 situations, all similar, which
definitely called for an air filter. They were all wind conditions with
blowing sand in the air. One was in the Antelope Valley near Willow
Springs, so I always bring an air filter to Willow. Another was at Laguna
Seca. The area just after what is now called turn 5 had sand blowing across
the track in such large quantities that it was only possible to see 150 feet
or so. I pulled into the pits, another competitor whose engine we had just
rebuilt did not. In 8 laps, the rings in his engine were totally worn down
to "nubs". After the race I think that we measured around 60% cylinder
leakage! Fortunately that was the only major damage to the engine. The
head required a fresh valve grind to repair the damage to the valve seat
from all of the sand, but the valves and guides were ok as were the pistons
and liners and bearings. The third instance was a Morgan that I bought that
had a lot of blow by. Whenever you got on the gas hard, you could smell the
blow-by fumes. It did not burn excess oil. Upon tearing the engine down,
we found that the compression rings were worn almost completely through.
That is the thickness of the ring, the portion that rubs against the
cylinder wall was worn to a thickness of less than 1/16 inch at a point
nearly opposite the ring gap. The thickness of the rings was not uniform
but varied as you went around the ring. The damage was clearly from
abrasive wear some time previously. I think that the engine had been run
for a long period of time after the damage was done as everything was worn
very smooth and there was none of the abrasive scoring that I had seen in
the race engine that was damaged by sand.
So, my recommendation, at least for Morgan where it is not possible to
fit a good air filter without installing an air scoop on the bonnet, is that
if you drive where there is the possibility of a lot of airborne dirt or
sand , then you should have air filters. If you drive where that is
generally not the case, and if you should get caught in a "sand storm" you
feel that you will be able to pull over and stop the engine, then you are ok
without air filters.
Regards, Greg Solow
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