Silk 98 in Derby Museum - who made the gearbox?

[gilesorton]

I visited the recently re-opened Silk Mill Museum, now renamed the Derby Museum of Making. They do have a Silk on display, though it is rather dusty and looks a long way from its best.

As best as I could see the engine number was 98. Reg GWK 681 V. Black. I will try to upload some photos.

The museum's description talked of the Silk being "assembled by Silk Engineering at Darley Abbey using parts made by themselves and other manufacturers. The forks and frames were made by Spondon Engineering and the gearbox by Velocette".  Is that final bit about the gearbox correct? I have been under the impression that    the gearbox was developed by Silk from a Velocette box in a similar way to that in which the engine was developed from the Scott?


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[hendred]

My understanding is the same as yours, Silk made or had made a gearbox based on the Velocette gearbox.  I believe Moss Engineering cut the gears. Matt Holder had the manufacturing rights to both Scott and Velocette so I can't see him letting George Silk have Velocette parts while in dispute over the Silk Scott name.   Many of the Velocette and Silk gearbox parts are very similar when side by side on the bench.  Paul may be along with the definitive answer from his research for his book.

[Garenne]

I have had to delve into the Silk gearbox internals more than envisaged when taking on the boxes of bits that constituted the makings of a Silk.   To me the gearbox is a direct copy of the Velocette design with some components interchangeable.   I had known that my bike had a racing history but didn’t realise what that meant until trying to assemble the bits.  It turns out that the gearbox internals were a special order from Silk and had the equivalent of a KTT Velo close ratio set.  This was achieved by replacing the standard 17 tooth sleeve gear with an 18 tooth version.  This took the first gear ratio from the standard Silk one of 2.29:1 up to 2.08:1.   Now I had heard that the standard Silk had quite a high first gear for road work and I had envisaged being able to use this bike two up on our local narrow hilly roads of Wales.  So I had to change it.  I managed to get Velocette drawings of the sleeve gear and it’s mating layshaft gear and discovered that the layshaft gear was identical.   The layshaft gears were easily obtainable from Grove Classics at very reasonable cost.  The sleeve gear however was also the same as the Velo component apart from an increase in length probably to accommodate the Silk clutch withdrawal mechanism.  I did consider trying to get an extension welded on to a standard Velo one which again was obtainable but didn’t quite like the idea.  Luckily I found an engineer making gear sets for classic and modern racing machines.   Looking at all the options available on the internal gear ratios I actually had two new sleeve gears made.  One with 17 teeth which provided the standard Silk ratios and the other with 16 teeth which gave a wider set of ratios equivalent to the old MAC Velos.  Both mating layshaft gears of 27T and 28T had been bought before hand to make sure the right gear form was used.

I have now done 2000 plus miles on the wider set of ratios and I won’t be bothering to try the other set of gears.  I was concerned whether there would be too big a gap between gears but the engine is so torquey that I just don’t notice any problem there.  I am actually surprised that this option wasn’t offered when purchasing these bikes new.  Not having ridden a standard ratio bike it is difficult to assess but I find this bike so rideable and have full confidence of not getting caught out on some unexpected uphill hairpin with these ratios even two up.  

[Smokey_Paul]

Very interesting on how you find first gear as I too would have thought it too high but if it works it works.

Correct the gearbox was designed around the Venom but really had no interchangeable parts because of tweaks as you found on the mainshaft.

Some did have a couple of parts as you found that are similar but are not Velo parts they were made by Silk.

Later gearsets made by Roger Moss definitely do not have interchangeable parts as he tweaked the gears etc for better strength and fit.

It's a real.jumble and can be potentially different model to model and bike to bike.