Triumph Repair: 1976 spitfire (USA), high octane fuel, spitfire 1500

Question
Purchased a used 1976 Spitfire cylinder head. It has been cleaned, magnafluxed, and ports appear to have been "grinded" smooth. Seller can't provide any history on the part. I would like to "mill" the head but don't know if it has already been done. Have checked all the usual references and am unable to find the height of a Spitfire 1500 cylinder head. Can provide any info or advice?

Answer
Hi Peter,

I have not been able to find that info which often comes up. Many auto machine shops had that data but I don't know if they had a source or just knew from experience as to how much they could get away with removing. If one has been already surfaced several times it will raise compression ratio and up set the rocker arm geometry.

The raised compression ratio will only make it necessary to always use high octane fuel (which you should be using anyway) and possibly make a slight ignition timing alteration. The rocker arm geometry however does need to be looked at. Normally there is enough adjustment in the adjusting screw but when you change rocker geometry due to a now long push-rod, you make the contact point of the rocker arm to valve stem different and thus place an excess side load on the stem which in time causes excess valve guide to stem ware. This can be corrected by adding shims under the rocker shaft stands.

On some engines valve to piston clearance (especially during valve over-lap)can be a problem when a head is shaved too much but the Spitfire usually has plenty of clearance unless a radical racing cam has been installed.

If it were mine, I would just have a auto machine shop check the head with a straight edge or make a light run on the surface to see if it needs to be surfaced and if it does go ahead and have them surface it with as little as possible to clean it up. Then assemble the head and rockers and put either bluing or just a little white lube on the valve stem and rotate the engine to get the valves to make a swipe across the valve stem and then remove the rockers and look at the markings the rocker made on the stems. If the makes are roughly centered It is ok, if it is on the inside only (toward the rocker arm shaft) I would make shims to raise the rocker arm stands up the amount the machine shop cut off the head  and check it again. As I remember that model has a fly-cut block and MUST have the correct head gasket installed. Don't put the flat head gasket on a fly-cut block!!! The gaskets look alike except for the ridge around the cylinder bore.

I don't think you need to go through the process we do on race engines of placing small dabs of modeling clay on the valves and / or the pistons to check clearance due to the excess clearance a Spitfire has anyway. Many use .020" minimum clearance but I always used .040" for very high RPM engines.

Howard