Unleaded Conversions

In 1920, leaded petrol was introduced to the motoring market as a fuel for cars. Unleaded petrol was introduced in 1986 and leaded four star petrol was subsequently phased out and withdrawn from the fuel market in 2000. Some garages offer leaded replacement petrol and lead replacement additives are available as are other options.

As a classic, vintage, veteran or heritage motorcycle or car owner, you may wish to convert to unleaded petrol after researching your options.

The leaded compounds present in leaded fuel provided the valve seats in the engine with a level of protection. Unleaded petrol does not provide this protection and problems arise due to ‘valve seat regression.’

Here the valve seats of the cylinder head are slowly worn away resulting in less contact surface area between the valve face and the valve seat and so the valves are unable lose heat fast enough. This can result in the valve “burnt out”. This can cause considerable damage to the engine. Some seats, having run on leaded fuel previously, may continue to function for short periods of use using unleaded fuel.

If you wish to run on unleaded petrol for sustained periods of time, then the best option is to have an ‘unleaded conversion’ on your cylinder head. At Chase Engines we remove the old valve seats and replace them with special hardened alloy valve seat inserts. These are then machines to suit your valves and the valves too can be recut and then the whole assembly vacuum tested verifying a tight fit. Due to a change in octane number, when using unleaded fuel, your engine’s timing will need adjusting to avoid detonation (pinking) rather than controlled combustion. Detonation can ruin an engine.

Unleaded Conversions

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