Sports Twin gearbox

[john9700]

Hi
I wonder if anyone knows this, the Villiers parts book lists different gearbox shell reference numbers for both 2T & 3T - I always thought they were the same?

Any ideas for this please guy’s?

C10246 (2T) & C11821 (3T).

[Brian Magee]

Hi John
I think it is because of the different crankshaft sprocket size. I fitted a 25 tooth sprocket to a 2T and the chain was extremely tight even without a gasket. Steve at Villiers Services said there was a difference at the crankcase joining surface to allow for the different chain length. The 4T has the same number as the 2T.
Brian.

[john9700]

Hi Brian
Thanks for your reply.

Visually their appearance seem identical, I have both kinds & think I need to
do a careful measure up.

I was simply wondering if it had anything to do with the 2T / 18T final drive,
compared against the 3T with 20T sprocket fitted?

If any further observations are found I’ll put them on.
Cheers.

[IanCordes]

It is an interesting question. The 2T & 3T have different crankcase shells, but I don't see why the gearbox shell would be different, and why a different size sprocket would require a different shell. The only difference I am aware of on the crankcases is the diameter of the apertures to allow the larger diameter 3T barrel spigot to drop in place, which wouldn't affect how the gearbox shell fixes to the crankcases.

Brian's point seems valid, except that the parts book states the only changes required when fitting a 25t engine sprocket is to change the 2 no. inner chaincase fixing studs, nuts and plain and spring washers to bolts and shakeproof washers. Also a 62 pitch instead of a 60 pitch chain, although that would indicate that going from a 20t to 25t engine sprocket.would tighten the chain, which would make sense of what Brian and Steve said. The Villiers manual makes no mention of changing the gearbox shell.

You seem to have hit on a bit of a puzzle there John, but that may well be the area to take your measurements!

Ian C.

[john9700]

Many thanks Ian for your thoughts, I’m beginning to wonder if it was simply done to separate Villiers inventory stock levels for production, so to enable flexibility between engine models should later model unique modifications be required or be dropped from the line up? They were used for a variety of vehicles remember.

So, I’m now thinking they are actually the ‘same’ - only differently stamped, though I still need to do the measurements.

It would be intriguing to learn if a similar thing occurred amongst any other engine type in the range, supporting interchangeability options like manufacturers often do?

Cheers