Classic Cob
From the shed
When attending the recent All British Rally at Newstead I came across a 350 BSA with an alloy head which had a different shaped rocker box. On speaking to the owner it transpired that this machine was fitted with hairpin valve springs. He believes that this is one of only ten produced by the Small Heath firm. Not being into the BSA marque I had no idea that they had ever made one. He advised that he also had an alloy head and barrel which he believes, but is unable to confirm, was possibly made in Queensland. I was able to photograph the machine and he later forwarded me photos of the alloy version. Wanting to know more about as to what is the benefit of hairpin springs, if any, I contacted an old acquaintance to find out more. His version is that hairpins came about due to the early coil spring materials not being able to handle the high rpm being achieved by modern engines. With high valve lifts being introduced in the 1920s and 30s there were also high failure rates. Another advantage was that these allowed better clearance around the top of the valve spring which helped in the cooling of that area. By removing the coil spring from the top of the valve stem it was possible, in some cases, to shorten the valve stem thus reducing the weight of the valve which is critical in high rpm engines. All of the Manx Nortons from the early 1930s on used hairpin springs were very successfully. These days however coil spring materials are so good that they can operate reliably at extremely high rpm even with the high valve lifts. The owner of the machine was able to forward to me some literature on the hairpin valve BSAs. It transpires that at the end of 1939 BSA developed a B29 Silver Sports with a cast-iron head and equipped with hairpin valves. A small few made their way to the civilian market. At the outbreak of war there was a military version – the B30 produced – but after the first batch left Small Heath, the army rejected this machine and went with the M20 BSA and other makes. After the war an experimental high performance version which was basically a B29 was prepared for the 1947 Junior Manx Grand Prix. BSA still had the rigid frame at this time so for this event the engine was installed in a frame with proprietary Feridax McCandless pivoted fork rear suspension and a large 9 inch front brake. It was ridden in this event by Irish trials and scrambles rider Bill Nicholson. Although the machine was quick it was not pushing for the lead and unfortunately ran out of fuel and did not finish. Nicholson also rode the machine in hill climbs and after signing a contract was employed in the competition section at Small Heath. In the 1970s an all alloy engine numbered EX291 with electron crankcases was located in the UK. The engine number EX291, is interpreted as Experimental B29, No.1. It is believed that this is the engine used by Nicholson and was built by Jack Emmott who was in charge of the experimental engine shop at BSA. Nicholson about that time is quoted in the Motorcycle Sport July, 1983 that he recalled that there were about three or four of those engines in the experimental shop when he was working there. Apparently coils later replaced the hairpin valve springs in late 1948 when they revived a model name that had been dropped in 1940 and this was to be the B32GS 350cc Gold Star, first of the post-war Gold Stars. Views are held that the post-war Gold Stars were descended not from the M24 500 Gold Star of 1938-39, but from the 1940 B29 350 Silver Sports. There is some mention of this engine in the book Goldie which I do not have access to.