dave williams
rec.autos.tech  10-07-92
- -> I'm looking around to buy an OLD Ford truck.  Does anyone know
  -> offhand what year ford switch their trucks from leaded to unleaded?
- Well, Ford didn't recommend leaded gas when it came out in the late
  '40s, but about '52 or so they said it would be OK, except lead buildup
  on the exhaust valves would cause burned valves eventually.
- Oh.  You mean thirty years after that, when they started taking the
  lead back out?  Depends on what load rating the truck was.

dave williams
rec.autos.tech  11-25-93
-    Tetraethyl lead was introduced to raise the octane rating of
  motor fuel when the high compression engines started coming out in the
  '40s and '50s.  The old style "eythl" gas had a *lot* of lead in it -
  valve damage from leading and channel erosion was quite common.
  'twarn't good for valves at all.

dave williams
12-02-93
- -> available as a fuel additive in 1923"  (I added the paranthesis)
- True, but you couldn't just drive up to your corner gas station and buy
  leaded gas until the 1940s.  Aviation fuel went to leaded before cars did.

[email protected] (Dave Williams)
2strokes  06 Apr 1994
- Back when "ethyl" was first introduced, mfrs used a LOT of tetraethyl lead.
  This let them use really crummy base stocks, which were cheap, and dope it
  with lots of lead, which let them sell "high octane" fuel at a much higher
  price.  Enough lead was used for deposits to build up on the seats.  Then
  the deposits would crack or chip, causing what mechanics then called
  "guttering," eroded grooves which leaked hot combustion gases when the valve
  was closed. The guttering would get worse and worse, until finally the valve
  and seat were too burned to seal.
- To combat guttering, OHV engines added valve rotators.  The first reference
  I have is for Oldsmobile, though there may have been earlier attempts.  The
  rotators would turn the valve slightly (usually a cam-and-ramp arrangement
  in the spring retainer) each time it was opened.  There were other benefits,
  like minimizing tip wear and guide wear, and evening out cooling on valves
  in combustion chambers with a noticeably "hot" side.
- The lead level dropped by the mid-'50s, and guttering pretty much
  became a thing of the past.
- During the early '70s the EPA mandated the availability of unleaded gas.
  Detroit had told the EPA they would need catalytic convertors to meet the
  '76 smog standards, and the EPA was smoothing the way. Catalytic convertors
  are full of sponge or honeycomb plated with a platinum/palladium alloy.
  When running hot enough - a convertor element will glow in the dark -
  various regulated pollutants would break down into other, nonregulated
  pollutants.  (I will spare the list my usual "regulated pollutant" flame)
  Voila!  To get the convertors to work, exhaust temperature had to be *very*
  high compared to older cars.  Lean mixtures and air injection to the exhaust
  ports did the trick.  Alas, the valves and seats of some engines weren't up
  to the thermal load of the smog systems, and promptly gave up the ghost.
  This was blamed on unleaded gas, though the actual blame was on the
  engineers.  To complicate matters, Chevrolet had some fairly horrendous
  quality control problems at the time, and officially blamed unleaded gas for
  burned valves to save face.
- Modern engines have improved catalyst designs, run a mixture close to
  stoichiometric, and have exhaust temperatures more like a '57 Chevy than a
  '77 Chevy.
- Some gasolines, such as Amoco, have always offered unleaded gas at the
  pump, though during the '60s it was simply labeled "Premium."  Octanes
  were in line with leaded fuels.  Low-grade unleaded gas was sometimes sold
  under the name of "white gas," since it was undyed.  (yes, gasoline is
  almost as clear as water; the individual grades are dyed for
  identification.)  Some "white gas," particularly the stuff packaged and
  sold in gallon cans, is actually naptha, which is very low-octane stuff
  and not much good as a motor fuel.