IML: Unleaded gas effects

["Dick Benjamin" <dickb@xxxxxxxxx>]

I have been an advocate of ignoring the supposed bad consequences of using
unleaded gas in our older cars - as most of you probably know, those cars
built before 1974 were not designed to be run on unleaded gas.

There are a lot of scary stories propagated by the automotive press and the
people who sell the "104+" and other supposed lead substitutes to "protect"
your car from the dreaded effects of running on unleaded gasoline, which is
all that has been easily available in most of the country since about 1984
or so.

One comment I have made on this mailing list and other places is that one
doesn't need to be concerned at all about this "problem" unless one is in
the habit of blasting across the desert in 100+ temperatures at 80 MPH+,
with a full load on (the car!). 

The problem is described as damage to the valve seats, usually called "valve
recession" in which the valves have been pounded into the seat so vigorously
that the seat metal is displaced or burned off, leaving an eroded valve seat
- ultimately resulting in the need for a "valve job" sooner than the usual
100,000 miles or so.  The symptoms of this damage are the same as any other
valve problem, leaking valves showing up as compression loss.  

This problem comes to all cars sooner or later, but running on unleaded gas
was supposed to hasten the day when you have to pull the heads off the
engine and send them off to your friendly local machine shop for a "valve
grind" (we're talking about overhead valve type engines here - flatheads
have the same problem and solution, but the machine shop needs the block
instead of the head to fix the problem.)


The above is to serve as background for the following:  I am preparing my
gold 1968 for sale on eBay - I've just finished my (nearly identical) 67 and
I plan to keep it, and sell the 68.  I've noticed that lately, when driving
the 68 with the AC on (which it usually is, with 100+ temperatures the norm
here in the high desert), that when idling at a traffic light, there is a
perceptible vibration from the engine - a sort of roughness to the idle
which is definitely not Imperial-like!  I did not want to sell the car in
this condition, as that would not be an accurate representation of what
these cars should be like to drive, and the car is otherwise quite nice.   

Accordingly, I followed my own advice and ran a compression check on it.  Lo
and behold, I had two cylinders that were down on compression - #2 was at 60
PSI, and #5 was at #118.  The other 6 were all at 150 plus/minus a few %.
(we're at high altitude here, so these numbers are about 10% low for you
flatlanders.) 

Since I had done the engine when I got the car in 1989, about 16,000 miles
ago, I was surprised at this result, and immediately pulled the heads off
for inspection.  

Guess what, folks:  I've got valve recession!  In spades, I've got valve
recession!  #2 and # 5 were both visibly down in their seats, and the others
were headed the same way.  

So, I took out the book I keep on each of my cars and reviewed the usage
this car has been subjected to in the 16 years I've owned it.  Almost all
the usage of this car has been in summer (read 110F plus) family trips
across the western deserts, from Palm Springs to Death Valley, Salt Lake
City, and Boise Idaho (all places where we have family gatherings).  The car
has always been our favorite long distance travel car, especially if we had
a full load of people and luggage, which we usually did on these trips.
Also, since usually the family was asleep during most of the trip, I just
set the ATC on 68 degrees and the Auto-Pilot on 80 or 85, and let'er rip -
for hours and hours on end. Since these cars run very cool, and get
reasonable gas mileage even at these speeds (we averaged 17+ on these trips
- I've got the data to prove it!) I didn't give a second thought to what gas
I was using or to "valve recession".  

OK, now I get to pay the piper!   

So, to make a long story only slightly longer, I am now putting in hardened
valve seats for the 68, for the first time in my history - after rebuilding
about 30 engines over the years and pooh-poohing the need for this, I see
the consequences of my past actions.  

I still feel that considering the way most of us in the hobby drive our
cars, and the environmental conditions most of you deal with, the addition
of hard seats is not worthwhile, but from this point on, when I think a car
is going to be driven HARD in hot weather, at high speeds with a heavy load,
I'm going to start recommending that hard seats be installed when ever the
heads are pulled for service.

So, to those who I might have mislead (no pun intended), I humbly apologize.
Sorry about that.

Dick Benjamin 



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