Following on from the successful production of pistons for OHV 500cc Sunbeam models Chris Odling and I thought it would be useful to produce some high-quality forged pistons suitable for the Model 6 side valve long-stroke. The Model 6 was produced from 1922 until 1939 becoming known as the Lion after takeover by ICI. With its 77mm x 105.5mm bore and stroke this was the last side valve powered motorcycle to win a Senior TT.
There were of course changes along the way and the piston produced is nominally compatible with models produced from 1925 until 1929. Before 1925 a 5/8″ gudgeon pin was used rather than the later 7/8″ type and the change to a scavenge pump from total loss oiling in 1930 means a different piston ring configuration is required. It is possible that these pistons could be adapted to suit.
I have limited availability of pistons in 77.0mm +0.000″ and +0.040″ sizes. An all-up weight of 434g has been achieved for the 77.0mm which is within 2g of the target weight that we set out to achieve.
Once we have given the new items a good look-over I’ll be contacting those who have reserved pistons already and adding them to the Sunbeamland shop.