Unleaded Conversion Process

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.

The Process
Cylinder head is stripped to a bare casting and checked for cracks and valve guide wear.  Worn exhaust guides must be replaced at this point.  Existing seat inserts are removed.

  1. A valve seat insert of suitable size is chosen and a counterbore is machined into the casting in place of the original seat.

  2. The counterbore is checked for size and depth.

  3. A high temperature polymer “sealant” is applied to the counterbore.  Once cured by heat, this substance has a melting point of 1800 degrees Centigrade (3000 Fahrenheit), and helps to conduct heat away from the valve seat and into the casting.

  4. The hard chrome-steel insert is fitted to the counterbore, and then machined to match the combustion chamber and port throat shape.

  5. A 3-angle profile is machined into the valve seat.  The new seat is checked for concentricity and is ready for the valve to be fitted.

The Risks
All water cooled castings have water jackets around their existing valve seats.  Cylinder heads that require Unleaded Conversion will be between 8 and 80 years old, and therefore have a certain amount of corrosion to their water jackets.  If a counterbore breaks through to a water jacket, the casting is scrap!  It is fairly easy to gauge how far beneath the surface the water jackets are, but it is almost impossible to know how much corrosion is present.  Readily available cylinder heads can be experimented on by machining the existing material until the water jackets are found.  With rarer castings this is not possible, so experience and (frankly) luck must be relied upon.  We will do our utmost to successfully convert any head or block, but will not be held responsible for any casting that has excessively corroded water jackets!  Please note that only a tiny percentage of castings will present problems.

Valves
At the time of manufacture, original equipment valves were not expected to have to cope with Unleaded petrol. Although most exhaust valves are made of suitably sturdy material, only very basic tests can be made to check their compatibility with Unleaded fuel.  We have access to a large range of valves that are specifically designed for constant use with Unleaded fuel.  To eliminate any form of guess work, we strongly recommend the replacement of original valves with the “known to be correct” after-market item.