starcain wrote:More Pics
Regarding the -60R #6 head Starcain showed with the unusual combustion chamber modification, I believe “55panman” called it correct here…..
http://www.harleykmodel.com/phpBB3/viewtopic.php?f=5&t=517&hilit=starcain&start=20#p3377
….. when he suggested that it is a modification motivated by the -69R head design, but for an engine with a flattop piston.
The trough across the head is essentially the same as a -69R head, but in this case, because it was for a flat top piston engine it has to terminate in a flat surface over the piston to provide squish. Although we don’t know what piston the fellow was using, it is possible that he may have had a near neutral deck, i.e., slight pop-up or no pop-up whatsoever, in which case milling the head gasket surface was required to obtain a reasonable squish band clearance. I believe the radiused squish band shape was done to simultaneously preserve as much squish area as possible while allowing adequate airflow to the cylinder.
We’ll never know the fellow’s true motivation for the modification, but everything appears to fall closely in line with the observations of 55panman. In querying other vintage racers, several have seen this design, suggesting this is not a one-off, but something that was attempted by other privateers too - likely post 1969.