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CHS Lead-Free Conversions

CHS Lead-Free Conversions for Classic Motorcycles and Automobiles

The Cylinder Head Shop helped pioneer the high quality Serdi equipment for use on demanding air cooled classic motorcycles before expanding on to remanufacture vintage automobiles.

With the legislation banning leaded petrol, it is necessary for the cylinder heads of most motorcycles pre-1984 and most automobiles pre-1988, to be converted to accept the extra heat of lead-free petrol.

CHS Lead-Free Conversions

Many owners of classic vehicles are concerned and confused by the current debate over what course of action to take. No one seems to know what to do. When 18 out of 22 fuel additives failed in recent independent testing, is this the most relaible choice to make? With the introduction of AV82, even light and vintage aircraft look to suffer.

In our opinion, practically every article and expert on the subject has failed to address two important issues. Firstly, the additional heat of unleaded fuel; and secondly, the effects of work hardening on some seats, in some engines that have given the wrong impression of successes being claimed..

We believe there is only one way to address this controversy and that is the proper way by replacing the original seats – but is that still enough?

The basic work necessary for a lead-free conversion is to replace the old exhaust seats with new silicon steel pre-machined rings strong enough to withstand the additional heat of unleaded petrol and the lack of lubricating properties.

Due to the heat of combustion, your exhaust valves and seats are almost at melting point. As they slam shut they can literally weld themselves together wearing out. Some vintage vehicles require new replacement stainless steel valves to match.

Although not absolutely required, it is also wise to re-cut your inlet seats to better than new and re-face your original valves. We do this to F1 standards on Serdi equipment to perfectly matching angles. It also makes sense to line your guides to close tolerances for the sake of longevity. Why?

See our page on K-Line Guide-lining.

This work is not entirely necessary but would add up to a head that will last two to three times the miles that a standard cylinder head would. The engine would start easier, tick over better and run stronger and cleaner. Not like new but better than new!

Some engines do need some other specific work done though. Due to the additional heat and characteristics of the flame front of unleaded fuel, some exhaust ports require a little gas flowing generally around the guide housing when pinking continues even after unleaded conversions.

We have discovered that this comes from the heat being reflected back into the combustion chamber and the only remedy is removal. After a high end unleaded conversion like this, it is not necessary to change the timing of the engine – but it is necessary to lean out the carburettion slightly.

Petrol Wash, LPG and CNG

It is important to check the carburetion after a conversion because too much fuel will cause “petrol wash”, literally too much petrol in the mix washing the lubrication away from the piston and barrels, from the valves and guides. Obviously, this will cause premature wear of the engine.

For owners considering converting their vehicles to LPG or CNG, extra consideration is due because these gases wear both inlet and exhaust seats very rapidly. Both inlet and exhaust seats need replaced and Serdi supply their “Star” range of seats for this purpose machinable on the new Serdi 5.

Further research in this area will no doubt uncover new and better solutions. Lead memory and work hardening may be a factor in old engines, so try your engine on unleaded and see what happens.

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