Original 1934 Scott 4 speed gearbox no 3412
Some years ago, I rebuilt the engine from a 1934 Scott for an owner who had inherited the machine from his grandfather.
When I delivered the engine, the owner showed me the other parts he had for the bike.
To my great astonishment, he had an original four speed gearbox no 3412.
I offered to check out this gearbox, well knowing that upon failing to cure endemic faults to the satisfaction of the majority who had purchased this optional gearbox, that Scott’s had offered to buy back the boxes and supply the well proven three speed gearbox as replacement.
The casing of this gearbox is stamped 3412 and is in good condition
When I first had opportunity to have the loan of such a gearbox in dismantled form, it was evident that there were several design flaws which did not allow the gear selection to operate reliably. This flaw had been the root cause of the majority of the malfunctioning, but this together with inappropriate design of the gear change engagement dogs had caused these to become severely damaged and malformed. At that time, I was fortunate to have the services of a young engineering graduate named Rob Sewell who had worked previously for George Silk and was an enthusiastic motorcycle racer. As our design office was a little short of work at that time, I asked Rob to measure and draw out all the components. Many years later these paper prints were redrawn by Ted Hills onto 2D CAD.
When the drawings were complete, we sat together mentally working through the actions of the design. When the wear and damage to the original components was assessed, it became obvious where the shortcomings in the actions originated. I have been lucky all my adult life in that solutions come out of the sky fully formed and it occurred again. I saw that by making a modified face cam, that we could provide a positive stop feature not incorporated in the original design. This luck visited me later when Rolls Royce asked our company to quote to manufacture a machine they had designed. The machine was to produce hot end jet blades for the Bristol Engines Pegasus engine fitted to the GR1 Harrier.
The design was not the simple and elegant offering that Alfred Scott would have smiled at, but another design fell out of the sky using different unusual principles. Rolls Royce were shown a model to demonstrate the principles involved and our company made machines to this system. The Harrier engine then produced considerably more power and the American Marine Corps bought the Harrier in GR2 form. Rolls Royce received the Queen’s award for technological achievement. I received a letter to thank us and say that the design of our machine was central to the successful upgrade of the engine. As I said, if the ideas fall out of the sky, then this is luck not cleverness.
Two boxes were made in about 1986 and the only reservation I have in retrospect was that I had opted to put an undercut on the dogs and dog pockets of 7.5 degrees. Once engaged the gears would never try and jump out of engagement, but the clutch needed to clear nicely if the gearchange was to be performed easily. I never had any problem with this, but if I were to make another set of gears, then I would reduce the undercut to 5 degrees.
As far as I am concerned, the design is sorted.
So back to original box 3412. The owner can not afford to have a new gearset made and he wishes to offer this box for sale as it stands to the highest bidder. If any interested party has a three speed box to offer as part of a trade, then all the better.
I will act as an agent for my customer, but am not involved financially. He is a good man with a young family and I just want to be sure that whatever he is offered will bring the best benefit to his family.
As to my involvement, I have all the drawings and example components that have been raced for more than 30 years. If I am having to manufacture new gears, then it will be much more economical for me to make another set identical to mine for this box.
Unfortunately I do not have gear cutting machines, so I must contract these operations out to specialists, so I am not currently in a position to give an accurate estimate for the rebuild of this extremely rare gearbox. I invite interested parties to contact me for any further information.
A buyer would not be restricted to me rebuilding this gearbox and could take it away to a specialist of his choice. The alterative face cam has been made already and is included in the sale. Roger Moss
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