Since this subject is more current overseass - here's some stuff from New Zealand, Australia, and Thailand.
I also have a lot of hard data from US and Canadian testing - but it's older since we eliminated leaded gas much earlier.
New Zealand
Valve Seat Recession
Exhaust valve seat recession (VSR) is a complex process affected by many factors of engine
design and use. Amongst these however, high engine speeds and high engine temperatures are
major factors in making an engine susceptible to VSR. VSR is a phenomenon experienced only
by poppet valve four-stroke petrol engines.
Valve Seat Recession Explained
Valve seat recession (VSR) is the name given to a process of accelerated valve seat wear. The
mechanism by which this occurs is as follows:
1. The very high temperatures at which it operates (typically between 600 and 800 degrees
Celsius) causes the exhaust valve to weld locally to its seat. When the valve is then opened a
small particle of the iron seat is pulled away. This particle is converted into iron oxide in the hot
exhaust gas.
2. As the valve then closes again these particles are imbedded in the valve face.
3. With these hard lumps of iron oxide imbedded in it, the exhaust valve becomes, in effect, a
grinding wheel. Thus any rotation of the valve will cause it to grind away the seat. Valves tend to
rotate under the action of the valve springs and by engine vibration.
Tetra ethyl lead, dangerous if absorbed through our skin when in pure form, is a form of lead
previously used extensively, and highly diluted, in gasoline. This compound has TWO major
effects. First, in sufficiently high percentage, it can raise the octane value a fair amount, very
important in WWII aircraft engines, especially those that were supercharged; some were both
supercharged AND turbocharged. The original purpose for using tetraethyl lead in gasoline was
specifically for raising octane. Some of those aircraft engines required 145 octane gasoline.
Usage for the purpose of raising octane was carried forward for decades for cars, because it
was cheaper, even when the lead was sold to the refineries expensively by the then Ethyl
Corporation, than using only refining methods to increase octane. Many decades ago, premium
(higher octane) gasoline's were simply called "Ethyl". Usually those gasoline's had MORE TEL
(Tetra Ethyl Lead).
The 'seat' and 'valve' protection effects were something noticed later on, after WWII [I think].
Tetra ethyl lead leaves a microscopic layer of lead on the valve and seat; some folks call this
cushioning. It was generally originally accepted that this effect, a 'lubricating', if you will,
prevents microscopic welding of seat and valve, or at least reduced metal to metal microscopic
contact, sort of how oil works.
Lead is, at very high temperatures, a LUBRICANT, AND A TERRIFIC CONDUCTOR OF
HEAT. The conjecture was that a small amount of lead makes the seat and valve much less
likely to weld at microscopic scattered points, and that the valve head heat is more readily
transferred to the seat. Lead was thought to generally totally prevent the welding.
Advice on the precise fuel requirements of a particular vehicle should be obtained from its
manufacturers, Where leaded fuel is recommended purely for its anti-knock or octane
properties the following options exist:
a) Adjust (retard) ignition timing to permit use of standard unleaded (95-octane) fuel.
b) Use super-unleaded (98-octane) fuel.
c) Use lead replacement petrol (LRP, expected to be 97 octane. Further information on LRP
later in this leaflet).
d) Modify engine to a lower compression ratio to permit use of standard unleaded (95-octane)
fuel.
Where leaded fuel is recommended to protect against valve seat recession (VSR) the following
options exist:
a) Fit hardened exhaust valve seat inserts. This is the approach used on modern engines
designed to run on unleaded petrol and is totally effective. However it can be expensive and is
not possible on all engines.
b) Use a commercially available lead-replacement additive in unleaded petrol.
c) Use lead replacement petrol (LRP).
What is the problem?
Lead additive in petrol prevented wear (recession) of the exhaust valve seat under the combined
effects of heat (due to combustion) and valve closure (hammering on the seat). Lead acted by
inhibiting impact welding of the valve on to the valve seat. Such welding, even on a microscopic
scale, eventually leads to a significant loss of soft metal from the valve seat in cast iron heads,
and allows the valve to sink further and further into the head.
The withdrawal of lead from fuel removes the protection your engine has enjoyed for all its life.
What exacerbates the problem?
a) Cast iron heads without hard seat inserts
b) Overheating
c) Sustained engine speeds above 3000 RPM
What can I do to reduce or prevent valve seat recession?
There are several options relating to choice of fuel and engine modifications. Your particular
choice will depend on pattern of car usage and the state of your finances.
Fuel Options
Use plain unleaded fuel
Probably OK for low mileage drivers who take it easy, and whose cooling system is in good
shape. Problems may not arise for some years.
Use LRP
Lead replacement petrol (LRP) contains alternative additives (potassium based) to combat
valve seat wear. The efficacy of these additives is unquestionably inferior to lead, but they will
offer limited protection (read the disclaimers!). They are widely available but moderately
expensive. The view is that branded additives used with unleaded fuel will provide a higher level
of protection, but this is unproven since LRP was not submitted for comparative testing.
Use Unleaded Fuel with Branded Additives
Do-it-yourself liquid additives are available. The Federation of British Historic Vehicle Clubs
carried out engine tests in association with MIRA and, as a result, gave its seal of approval to
several brands including Superblend 2000, Nitrox, Redline, Castrol Valvemaster, and Millers
VSP all of which performed acceptably well. These additives have different chemistries and the
advice is not to mix them; choose one and stick with it. Rumour has it that Superblend 2000
performed best under test, and has the advantage that its chemistry is compatible with LRP in
case you run out.
Note that some of these additives are also available with an octane booster component.
Engine and Other Modifications
Install Fuel Catalyst Pellets
So-called fuel catalyst pellets (often tin based) can be installed in the fuel tank or in-line feeding
the carbs. Rely on them at your peril. They’re inert and won’t do harm, but neither will
they provide any protection.
Install Hardened Valve Seat Inserts
Specialist engine machine shops can machine out your cast iron valve seats and press fit
hardened valve seat inserts which will resist wear and enable the use of unleaded fuel without
additives. Only the exhaust valve seats need to be replaced. Cost is moderate and performance
should be reliable if the job is done properly. If it isn’t and the inserts drop out, you’ll
probably need a new head and an engine rebuild.
Install an Alloy Head
The ultimate modification. Aluminium alloy heads come ready fitted with special valves and
seats. You can run unleaded fuel indefinitely, obtain better engine performance due to the
improved head design and carry a lot less weight! However, they’re expensive
Valve Seat Recession and Protection Due to Lead Phase Out in Thailand
As the consequence of air quality deterioration and the car overpopulation in Bangkok
Metropolitan Area, unleaded gasoline was introduced in 1991. In using unleaded gasoline for
cars with soft exhaust valve seats, their recession was found to be excessive after only 3,000 -
12,000 km of usage on the highway at 120 km/h. Such cars represented about 15 percent of
the national car population in 1993.
Using an anti-valve seat recession additive is one solution used to prevent valve seat recession.
An engine test simulating field conditions to evaluate additive effectiveness was implemented.
Potassium-based and sodium-based additives were tested and the test results led to the
conclusion that the effective anti-valve seat recession additive treat rate suitable for car
population and driving condition in Thailand was 10 mg of potassium or sodium per kg of fuel.
Unleaded gasoline with anti-valve seat recession additive has replaced leaded gasoline in Thai
market as of 1995. Finally, leaded gasoline was completely phased out as of January 1, 1996
by Government regulation.
Australia
Engine Dynamometer Studies of Potential Component Wear in Vehicles
Using Unleaded Gasoline
Fixed bed dynamometer engine tests were performed to study the phenomenon of valve seat
recession which can occur in motor vehicles operating on unleaded gasoline and not fitted with
hardened valve seats. In conjunction with these tests, an investigation into the effects of using
low phosphorous crankcase oils was carried out. The overall conclusion was that the
uninformed use of unleaded gasoline and/or low phosphorous crankcase oils can cause severe
engine component wear
Valve Seat Recession in pre-1986 Vehicles
Most cars that use LRP were built before 1986 and have valves in their engines which require
protection from valve seat recession.
Valve seat recession is the wearing down of the exhaust valve closing surfaces in the engine by
abrasion and corrosion. Excessive wear can result in the loss of compression, power, fuel
efficiency and engine performance.
With leaded petrol, lead protected valve seats against wear. LRP was introduced in its place in
2000 to offer the same protection as leaded petrol without the health and safety concerns. LRP
combined a specially formulated 96 octane rating unleaded petrol with a non-lead additive
which protects against valve seat recession.
Who will be affected?
Only cars manufactured before 1986 are affected.
Some pre-1986 vehicles do not need AVSR protection but require fuel of a higher octane than
unleaded petrol to prevent the engine 'pinging'. These vehicles will need to use higher octane
petrol such as Shell V-Power, Shell Premium Unleaded or Shell Unleaded 95.
Only cars that required LRP to protect against valve-seat recession will need to take additional
action to protect their engines. These cars will generally require a premium unleaded fuel such as
Shell V-Power, Shell Premium Unleaded or Shell Unleaded 95
2. AVSR Additive
AVSR additives act as a solid lubricant between the exhaust valve and the soft exhaust valve
seat, preventing the valve from recessing into the cylinder head.
.....dont matter what its called, I just call it mine now! I love this thing, its fun!!!
