I'm thinking that perhaps the unleaded fuel troll has
finally caught up with me. While driving the SIII
the other day, I noticed that on the steep, mile-long
hill going up to my neighborhood, a hill I take in
3rd gear at about 3,000 rpm, about halfway up
the exhaust had a very "airy" sound as opposed to
its usual burble. The rpms didn't drop, and I
didn't need to add more fuel to maintain speed.
But at the top, when I would shove in the clutch
to let the rpms drop to idle, the manifold pressure
gauge pulsed a lot, not unlike having a badly mis-adjusted
or burned valve. After driving on the level for a few
minutes, the fluctuation went away when I let the
engine go to idle.
It starts fine, idles smoothly, etc otherwise. It's just
the hill climb that results in the odd exhaust pulse and
fluctuating manifold pressure (at idle). So I'm
thinking that perhaps one (or more) valve clearances
have moved to the point where as the engine heats up
on the climb, the valve(s) don't close properly anymore,
resulting in the airy sounding exhaust and fluctuating
manifold pressure. As the cylinder temperatures go
back down, the valves return to a more normal seating,
although if this is what's happening, the clearances are
obviously way too tight even for "normal" conditions.
I'll check the valves before I drive it again, but since I
last adjusted them only a thousand miles or so ago,
I'm starting to suspect I'm getting valve seat recession in
at least one valve if not more. Back in the 70s and 80s
when I was driving the vehicle every day, the valves
needed checking only a couple of times a year, and even
then there was rarely much adjustment to be made. The
last time I adjusted them, however, prompted by a rhythmic
spit in the exhaust and a pulsing manifold pressure gauge,
I found all the valves were fine except the very front one,
which had no clearance at all. Adjusting this cured the
exhaust and pressure symptoms, but I'm beginning to
think a new head, or new valves seats and valves in this one,
will soon be in order.
It's not unexpected. I figured it was just a matter of time
before I'd have to do it. But if any of you have experienced
a similar symptom, particularly with a leaded head engine,
I'd be interested to hear what you found.
___________________________
C. Marin Faure
(original owner)
1973 Land Rover Series III-88
1991 Range Rover Vogue SE
Seattle
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