7 port cylinders?

[Normandale]

I wonder whether or not 7 port cylinders were ever used on Villiers engined bikes back in the day? Today they seem very common, and some trials bikes are even fitted with reed valve conversions!

The 7 port motors seem to run pretty much like a modern twin-shock, and the originals seem to have a lot less go and appear rather lethargic in comparison.

[John Wakefield]

Question is why did Villiers not make them like that then, maybe they would still be in business.

[Peter Rotherham]

7 port cylinders

I think that the simple answer to this one is expediency. The Villiers Factory was a manufacturing mammoth, turning out thousands of parts for hundreds of engine types. Costs and plain old complacency kept them churning out the same parts for years. 'New' designs were merely slight adaptations of the old, take the 32A vs 37A, cut a few farings off, reduce the amount of Alloy needed around the Clutch, and you have a 'new' engine, (and a saving in material per unit). Villiers just churned out units, it was up to the endusers to vary them, as Greeves did.
Had the technology been available, and the push to uprate Motorcycles into the Superbikes of the 70's, (As the Japs did), then Villiers could have lead the world in 2-stroke engineering. If you've ever worked on the early Jap 2-stroke twins, they were jewels of mechanics, but finnicky to set up. Even so, not too far removed from a 4T engine in overall design. Better primary compression, Cranckcase injected lubrication, lighter cranks, higher piston speeds, reed valves, all used by the Japs, could have upped the bhp output from the 4T to a competitive level with the Super 6 or YDS 1.

[John Wakefield]

And shorter stroke, wonder if these 'trick' 37A trials engines have a shorter stroke! The long stroke of the Villiers must be a limiting factor.

[Normandale]

Unless Villiers were able to access the information related to 2T engine development provided to the Japanese by Ernst Degner (MZ works rider), its not likely they would have been able to come up with anything to rival the Japanese!

Modern trials motors still retain the long stroke design, but some are now using special 8 port cylinders. Using a shorter stroke and a reed valve would probably work very well, but I think this may be a non starter due to the crank wheels being too large diameter, and possible issues with primary compression ratio.