CASTING THE DIE ON THE CB750
Thanks to Gez Kane for the great ‘Buying Guide’ article on the CB750 in the February issue. I’m an ex-pat Kiwi who has lived in Tokyo for nigh-on 50 years and have been involved in advertising copywriting for Honda motorcycles and as well as being a general Englishspeaking gopher for Motorcyclist magazine in that time. I spannered for two friends at the rejuvenated Suzuka Endurance race on an early CB750 and was involved with RSC through running a CB125S over-the-counter racer here.
I feel it’s time that someone finally took the bull by the horns and either confirmed or exploded the story that the first 7414 or so CB750 engine cases were ‘sandcast’. I used and abused several examples of both the ‘sandcast’ and later die-cast engines and can only say that the first batch were much better castings than any sandcast items I’ve come into contact with. Slightly rough, yes, but not too far away from the quality of the later units.
At our yearly Good Old Days track meet at the Twin Ring Motegi circuit a couple of years ago, I got into a conversation with an elderly man who was involved in the early development. He told me the ‘sandcast’ moniker was a myth. Due to a rush to get bikes on the export boat, there was not enough time to finish the pressure die-cast moulds and that initial run was gravity die-cast in slightly inferior, rougher moulds – but definitely die-cast.
Once the final moulds were complete, they switched to pressure die-casting and the superb finish we are all familiar with. This was confirmed in an article on American, Vic World – who at the time was building complete early CB750S from NOS parts – in December 2003’s Classic
Bike. It said, ‘The very first CB750S are known as the ‘sandcast’ models because of the grainy texture of the engine cases. They were in fact die-cast pieces, using roughly finished moulds.’
PS: The RSC kit racer lives on: see below. Malcolm Moore, Tokyo This is a contentious subject. Some CB750 ‘experts’ swear the cases were actually sandcast, while others insist they were gravity diecast. As far as I know, there is no-one who was directly involved in the production process at Honda who has ever cleared this up with the benefit of first hand experience. Gez Kane