The BSA Workshop > Lightweights

BSA Dandy Aluminium Cylinder

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When launched at the 1955 Earls Court show, the BSA Dandy was advertised as using a chrome plated aluminium cylinder. Aluminium was needed to better dissipate the heat from the rear facing cylinder since cast iron has a much lower thermal conductivity. However, by the time it went into production in 1957, the accepted view was that the aluminium cylinder had been replaced by a cast iron one since BSA had failed to fully develop the aluminium chrome plating process by that time. Unfortunately, this change then led to cooling problems with the engine.

Intriguingly, I have Dandy engine DSE 365 which is fitted with a chrome plated aluminium cylinder. I'm not sure where the engine originally came from but it's engine number relates to a BSA Dandy produced in 1957 which seems to be at variance with the normally understood development history of the bike. It seems to suggest that the Dandy originally went into production with the chrome plated aluminium cylinder but was quickly changed to a cast iron one, presumably, due to premature wear of the chrome.

It would be good to hear from anyone with an early Dandy who might be able to shed further light on this issue or who has an engine with an aluminium cylinder?

Hello Arthur

Dont have a Dandy but blue top service sheet number 36 from May 1957 mentions both types of cylinders on the second page. You can see it in the members area but the copy there is missing the second page. I have attached the complete sheet below.

There are as far as I can see 14 different blue top service sheets referring to the Danday starting with number 28 (speedo fitting) issued in November 1956 and ending with number 60 (neutral finder twist grip conversion) issued in November 1958. 11 of these can be found in the members area (Missing 31 51 and 60).

There is also service information - 9 pages - for the Lucas 6F1 and 8F1 generators in the Lucas Digests for 1956/57 and 1958.


Many thanks for that. The second page seems to confirm that the early production engines were indeed fitted with chrome plated aluminium cylinders and also confirms that the Dandy went into production before adequate development testing had been carried out. A few months later, presumably after problems with the chrome coating, a change to cast iron cylinders must have taken place!

The chrome on my aluminium Dandy cylinder is badly worn in places and it's surprising that this wasn't changed to a cast iron one back in 1957. How this engine survived to the present day with its original aluminium cylinder is a bit of a mystery!

This service sheet from December 1956 shows more lack of testing before release to public.

It is interesting to see how much these service sheets reveal about the state of readiness of the Dandy when it was put into production in the 1957 season. Within months, they had to change the cylinder barrel design and they had to reposition the pivot points for both the centre stand and the rear brake pedal, the latter originally projecting up through the floor pan and then having to be moved to pivot above it. They also had to abandon the original hand operated starter lever and replace it with a conventional, albeit LHS, foot operated kickstart. One would have thought most of the problems should have been spotted during development testing?

I wonder if there are similar service sheets revealing problems with the introduction of other BSA models?


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