The Rocker Base gaskets were originally developed to solve some problems in this leak prone area. They are very much more stable than the original style items. I was also surprised when using some for the first time that the 'feel' of the head bolts through the torque wrench was very different. The suggested jointing compound to use on these copper gaskets is a thin smear of silicone (RTV) rubber.
The Rocker Base gaskets are available in two thicknesses: 0.6mm (which is 0.024") and 1.00mm (0.040"). The thicker version is useful if there are valve top collar to rocker clearance problems. These problems can occur is the valve seats are worn or the head has been overskimmed in the past on the top surface.
The Cylinder Base gaskets were developed to increase the stability of this joint and to allow small variations to be made in cylinder position. Under racing conditions original cylinder base gaskets occasionally failed. It had also become necessary to be able to control accurately the position of the cylinder block to allow adjustments of compression ratio, and in squish engines the squish clearance.
The Cylinder Base gaskets are available in five thicknesses: 0.3mm (0.012"), 0.4mm (0.016"), 0.5mm (0.020"), 0.6mm (0.024") and 1.0mm (0.040"). Moving the cylinder by a greater range than this can cause cam timing and follower positional problems, as the tappet blocks (and therefore the cam followers) are set at a small angle to the cylinders and vertical movement does affect their position with regard to the camshaft.
Copyright © 2000 Philip Pick
Version 0.1 Date January 2001