Setting up valve guide clearances

Dear Jon,

We have been modifying TR-4s for unleaded here in California for going on to 20 years now. The guides that we use are a molybdenum bronze material but we have also use phosphor bronze and aluminum-silicone bronze. We recently did a 1956 AC ACE also. The ACE was set up with the clearances that you mention in your posting and had valve stem seals also. We have problems with "squeaking" from the inlet valves and guides until we removed the seals! The coefficient of expansion of the bronze alloys is so much higher than that of the cast iron head that as the temperature goes up the valve stem to guide clearance goes down. We have actually had exhaust valve seizure problems on a hot engine when the valve stem clearance is less than .002". What we normally use and have had good success with is .0015" clearance on the inlet valve stem and .002 to .0025" on the exhaust valve stem. These are run without valve stem seals on TR-3s and TR-4s that have had the rear camshaft journal modified to increase the amount of oil supplied to the cylinder head and valve gear. With these clearances and using stainless valves with hard chromed stem we have had neither oil consumption nor seizure problems and have had great durability even under extreme racing conditions.

Regards,

Greg Solow
The Engine Room
Santa Cruz, Ca.

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