Because of CNC machining commitments we are now unable to undertake any engine work, these pages remain for information purposes only. But – we will be happy to find someone to help with your job, please phone or e-mail if you need a recommendation.
Q – Why do engines need modification to run on Unleaded?
A – Lead that is added during the 4 Star manufacturing process acts as a high temperature lubricant, and stops the hot exhaust valve micro-welding itself to its “soft” cast iron valve seat. The exhaust valve may operate at over 700 degrees C., and 75% of it’s cooling is by transferring heat to its valve seat. The fitting of a hard exhaust valve seat and the use of a suitable exhaust valve stops this micro-welding process.
Q – What about Lead Replacement Petrol (LRP)?
A – It appears that LRP may not provide enough protection. To quote the Department of the Environment in their bulletin – Making The Change To Lead Free Petrol – “If your car is often used for motorway driving or towing and it cannot run on Unleaded petrol you should consider having hard valve seats fitted to the cylinder head.”
Q – Do the valves always need to be replaced during Unleaded conversion?
A – From a material point of view the inlet valves almost never require replacement, and most exhaust valves are already made of a suitable material (a quick check can decide this). Worn or damaged valves must be replaced automatically.
Q – Why isn’t the inlet valve seat affected?
A – Because the inlet valve and seat are being constantly cooled by the gases flowing past them.
Q – Do all cylinder heads have to be converted?
A – Every cast iron cylinder head will need to have hard exhaust valve seats fitted, whilst every aluminium head already has valve seat inserts fitted, some of which are already capable of running on Unleaded fuel.
Q – Do I have to alter the ignition timing?
A – The vast majority of engines will be able to retain standard ignition settings. Only very rarely will it be necessary to retard the timing by 2 or 3 degrees, but this should only be done if any running problems are experienced. Modern high octane fuels usually allow standard settings.
Q – Should I think about lowering the compression ratio of my engine?
A – Again, most engines will run perfectly well. A rough rule of thumb is that a compression ratio of up to 10.5:1 is OK (some modern engines have a C.R. of over 11:1 and are specifically designed to run on Unleaded).