Lead Free Motoring

When lead free or (lead replacement petrol) is used in an engine originally designed for operation on leaded fuel there is a high risk that valve seat recession (VSR) will take place. Even with continual monitoring and adjustment of the tappets, VSR can happen very suddenly causing terminal damage to the head and possible other parts of the fuel system of your TR.

Valve seat recession is the name given to a process of accelerated valve seat wear which occurs at very high temperature (600º – 900ºC) and 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. As the valve then closes again these particles are imbedded in the valve face, and the exhaust valve becomes, in effect, a grinding wheel and any rotation of the valve causes it to grind away the seat. Valves tend to rotate under the action of the valve springs and by engine vibration.

To avoid VSR the engine must be kept below the critical temperature, (which would mean keeping below 3500 revs for most TR engines) with no periods of sustained high load such as when towing, or long periods of motorway driving. The alternatives are to use one of the FBHVC endorsed chemical additives, or make mechanical modifications, or of course do nothing and wait until there is a problem.

MECHANICAL MODIFICATIONS

TR2 – TR4A wet liner four-cylinder engines
If the cylinder head is in good order then fit hardened valve seats as a minimum. There is a greater than 50% chance that the head will be cracked however, and the alternative is to fit a new cylinder head. These are available through major suppliers and a brief telephone enquiry to them will enable you to budget for the purchase of a head plus the new valve guides and springs which may also be necessary.

TR5 – TR6 fuel injected six-cylinder engines
There are no test results for the effect of chemical additives on TR5 and TR6 metering units. These units were designed so that the lead in petrol lubricated the very tight tolerance rotor and shuttles. The seals also have a “chemical memory” and using unleaded petrol could cause a problem in some cases.

A few years ago there were reports of cars catching fire in New Zealand because of seal failure after using unleaded petrol. This petrol contained, in error, an unacceptably high level of toluene and the “chemical memory” of the seal caused it to fail when in contact with such high levels of a different solvent. The chemical constituents of unleaded petrol now sold in the UK (and now in New Zealand) would be less likely to cause a problem and all new seals will be compatible with unleaded petrol.

Replacing the seals is best left to an expert, so the answer could be to replace the whole metering unit. Any of the Recognised Suppliers would be happy to advise. The six-cylinder heads can also be modified with hardened valve seats. New heads are not available.

TR7, TR7V8, TR8 Rover engines
These engines were designed to run on unleaded and should already have hardened valve inserts. Officially Rover has never admitted this, but the vast majority of the cars went to the USA when leaded petrol had already been withdrawn.

OTHER POINTS OF NOTE

Leaded fuel: Although this sheet is about unleaded fuels, there are still some locations where leaded fuel is available in the UK. Visit the FBHVC's website (use this link www.fbhvc.co.uk/fuel information) where you will find the latest information on availability and location. There are fewer and fewer sites and they do not provide enough locations to enable any sensible touring with a TR that requires leaded fuel. The price of 4 star leaded petrol at time of writing (Jan 2010), is £1.80 per litre.

Ethanol in fuels: There is also current advice on the FBHVC site on latest changes in fuels and their effects. For example 5% Ethanol, (a bio fuel), is being introduced in fuel supplies in the UK. At this level it is currently thought that no changes are needed to any of the settings for TRs. In other mainland European countries, levels of ethanol in petrol can be much higher (up to 25%) and can result in noticeable increases in running temperatures which may not be suitable for use in a TR. Always check the pump when buying and ask for further information. Do not assume the pump will say how much bio fuel will have been added and unless you can establish the actual level or if it is clearly more than 5% it is probably best avoided.

(With thanks to the FBHVC and Glavon Group for their assistance with this information sheet)