Unleaded stuff

Cylinder heads

Leaded fuel leaves a small deposit of lead on the valve and the valve seat which protects them from the hot gases rushing by. The inlet valve is protected
naturally as it is constantly cooled by the fresh mixture, so that's not the problem, but the exhaust valve takes the full impact of the heat. Heads which
are prepared for use with unleaded fuels have specially hardened materials used for exhaust valves and seats to do without the protection of the lead.

Engine numbers

If the engine is still all original, use the engine numbers;

1275 Austin Metro engine fitted with unleaded heads : 12HE24, 35, 39, 40, 41, 42, 67 up to 75.

MG Metro 1300 unleaded post mid-1989 fitted with unleaded heads : 12HF01

MG Metro Turbo unleaded : 12HF01

Also, is someone had taken the car to a ROVER dealership for the 'ROVER approved' unleaded conversion, the ROVER bulletin that was issued with the corrected
timing figures, also stated that the fitter must stamp a 'U' on to the engine plate.

An example;

MG Metro 1300 leaded fuel pre 1989  12H996AA, would be 12H996AAU

Its fairly obvious because it would be stamped in and not raised like the other letters.

Unleaded Fuel as Standard?

Minis made after May 1989 can run on premium (95 RON) unleaded or any mixture of the two without modification.

(BELOW added 21 november 2002 from Dennis Watts)

Here is a list of 998cc engine numbers which are compatible with unleaded.

These refer to mini engines produced from 1989 onwards.

99H/D81P, 99H/E20, 99H/E21, 99H/E22, 99H/F16, 99H/F15, 99H/F32, 99H/G30, 99H/G31, 99H/G32, 99H/G33, 99H/G34, 99H/G39

all post 1990 1275 mini engines were unleaded compatible.

all previous engines require modification before they can use unleaded.

Information, from Barrett's MG-Rover, folkestone. www.barrettskent.co.uk

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Unleaded fuel, Article about valve seat recession

Triumph Valve Seat Recession and Unleaded Fuel

by B. John Mitchell,
15 March 1996

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The problem of valve seats in internal combustion gasoline engines became apparent with the gradual fazing out of leaded fuel in the late 60s and early seventies.
Lead in the fuel accomplished more than increasing the knock value of a fuel. When the auto companies began testing "virgin" engines with unleaded fuel, valve
seat failure was encountered within 10 to 20 hours during a wide open throttle 4000 rpm durability test. Lead in the fuel provided exhaust valve seat lubrication
and excellent heat transfer from the hot exhaust valve to the seat in the head than to the coolant media.

Several methods were tried to fix the problem, including seat inserts, valve rotators, and cooled valves, either sodium filled or a "heat pipe" design. I ran all types
of designs including the "heat pipe" and also with a jet of coolant (water) sprayed directly on the valve. It became apparent that keeping the valve cool was a
good solution but costly. The hardened valve seats became a cost effective compromise and was adapted by most if not all of the manufacturers.

With the effect of unleaded fuel under control, the next step was to incorporate a catalytic converter to reduce the level of CO and HC. A catalyst reacts
very quickly to an increase in unburned fuel causing a catastrophic catalyst failure within microseconds. Thus it was apparent that the then widely used
breaker point ignition systems in use would allow the engine to operate, although poorly, and cause a catalytic catalyst failure. This began the expedited
development of a breakers or electronic ignition distributor, referred to as a "walk home" design since if the distributor began to fail, the engine would stop
preventing any costly catalyst damage. With the advent of relatively inexpensive on board computers, electronic fuel injection was introduced as well as
non rotating ignition systems all receiving inputs from sensors located in strategic necessary location sensing temperatures, fuel mixtures and exhaust makeup.

First, there never was a "requirement" for valve seat treatment, it was up to the particular automobile manufacturer. Further, I mentioned valve seat failure
(valve seat recession) on a "virgin" engine. If the same test was applied to an engine that had been run with leaded fuel, the valve seats did not fail. There
is a sufficient quantity of residual lead in the system affording protection and very few engines are ever subjected to the durability type test that produces
a valve failure. In the case of your Triumph, you should encounter no problem using unleaded fuel. In the test that I mentioned, valve seat recession
measured 0.000150 to 0.000180 of an inch in 40 hours of wide open throttle, 4000 rpm operation. Incidentally, valve seat inserts are not a good solution
because of the expansion differences and the tendency for the seats to loosen - staking the seats only aggravated the situation in the long run.
Hardening the seats was a good compromise (the depth of hardening is only .030 or so). Enough said!

B. John Mitchell, 15 March 1996

(Mr. Mitchell retired from GM in 1975 after 37 years. He was involved with engine development during his tenure. One of his more well known engines
was the Buick aluminium V-8 designed in the early 1960s and still in production today as the Rover 3.5 family. He was also involved in the development
of the current Buick 3.8L engine.)

Unleaded with high CR

UL in an engine running a CR > 10:1?

When considering compression ratios the use of leaded/unleaded fuel is irrelevant. Its the octane rating that matters - and while t.e. lead is the
cheapest way of raising octane rating - there are lots of other solutions (more expensive and more dangerous that is).

Leaded/Additives with Catalytic Converters !!!!!!!!!!!!!!!!!!

you will probably destroy your CAT & Lambda Sensor if you feed it LEADED PETROL, L.R.P. or other additives NOT approved for catalytic converters!!!!