Tuesday 2 March 2010

Overhead Sidevalve Norton - SOLD

This Norton is SOLD for sale at Yesterdays. At first glance a normal sidevalve 16H Norton but when you look more carefully you'll note that the inlet stub and the exhaust pipe are not where they ought to be. Some clever modifications went into this engine, apparently in the way the valves are situated.

The engine was discussed in several issue of Old Bike Mart and above is one of the suggestions as to how it could work. In this setup, the valves are opened by the valve springs and closed by the cams. A flaw in this design is that tappet clearance is still required (metal expands when it gets hot) and as the valve springs open the valves, the valves will not close completely unless forced to do so by the cylinder pressure of a running engine. 

This very nice drawing (above) is another suggestion as to how it could work and frankly, I don't get it; there is still a provision for tappet clearance but now the valve springs close the valves; I don't understand what opens the valves unless these "yokes" could pull the valves open in the presence of tappet adjusters.

The photos above show how it actually works in this Norton's engine; the valve springs close the valves as in a normal engine but the modified cam followers pull the valves from their seats. The valve seats are in the cylinder head now and the valve heads are reversed, as predicted.

So what problem has been solved? In my opinion no more than a slightly more efficient gas flow; less bends to take and perhaps a little bit more performance! On the downside, there is a lot of ''play'' in all the parts that move the valves around and it is hard to envision that this engine will be either very quiet or rev like a proper OHV machine.

Thijs of Yesterdays assures that the machine runs very well, and it looks looks like a lot of love and care went into it's construction. A real opportunity to buy a truly unique part of motoring history!