Re: 3rd series single six engine

Posted by Richard Sturdy On 2017/5/18 4:03:38

The "Squish" head came, I believe, with the 3rd Series Single Six engine. Basically, the 1st Series head had the combustion chamber and spark plug directly above the cylinder and the piston top protruded into the chamber by about 1/8". The "Squish" head was completely different, in that the piston top was flush with the block surface at tdc and the head was flat above the cylinder, with a wedge-shaped passage to the combustion chamber above the valves. The spark plugs are directly above the valves. The whole idea was to create turbulence in the mixture charge prior to ignition. This encouraged more complete combustion and more efficient conversion of the fuel into energy, giving increased power and improved fuel economy. I believe that the squish head also runs at a higher compression ratio. The difference in performance between my original engine and the rebuilt unit is remarkable and we put much of this down to the fitting of the 3rd Series head. The engine now has a 1st series block and all ancillaries (manifolds, carb etc) with the notably heavier 3rd series bottom end and 3rd Series head. We used alloy pistons with flat crowns and incorporated a spacer between the crankcase and the block to ensure that the pistons were exactly flush with the upper face of the block. As mentioned previously, it has been bored out to 87mm. This "hybrid" configuration was forced upon us by the fact that we did not have enough sound castings to produce either a full 1st Series or a full 3rd Series engine. The result however, is very satisfactory and I am truly delighted with the increased performance and flexibility which it delivers.