Motorcycle Engine
Built by Frank Paine in July 2001
A full-size model of a twin-cylinder, four-stroke motorcycle engine with overhead valve based loosely on the 1950s № 10 outfit Special Model Leaflet.
It is ‘cut away’ to show its operation and includes working valve gear, sparking plugs, and most other details.
This is loosely based on the № 10 outfit special model leaflet of the 1950s, and the model is in post-war medium red and green Meccano. All the mechanical elements of the basic engine are represented, including crankshaft, con rods and pistons, camshafts, push rods, rockers and valves, all moving as in a real engine. These all operate in a cut-away shell representing the crankcase, cylinder block, cylinder head, magdyno and exhaust ports.
Many parts of the model have been redesigned, compared with the leaflet, including the base and the crankcase construction, which has been left partially open so that the crankshaft can be clearly seen. The crankshaft itself, with its flywheel and bob weights, has been considerably modified in the interests of greater realism, and the timing side bearing has been filled in for the same reason.
The timing case has been made much neater than the rather clumsy original, and the cover left off to reveal the chain drive to the camshafts and cam followers, which have themselves undergone minor improvements. The original con rods were very spindly and too long, so these have been shortened and redesigned to make them more realistic.
The finning to the cylinder block has been totally reworked to make it neater and a more regular and logical outline, with deeper fins around the head, and all flexible plates in the original design of the block have been replaced by flat plates, for rigidity. There have been minor improvements to the carburettor and manifold, but the valve gear has been totally redesigned. The original Meccano compression springs still operate the valve return action, but as these are so minute and out of scale, they are hidden in this model, and the valve springs are represented by worm gears. The valve guide arrangement is therefore totally different from the leaflet design.
Spark plug suppressor caps have been added, and the spark and vapour ignition, which operates correctly every other stroke, is represented by a flashing orange light in the combustion chamber, controlled by a Meccano commutator.
The engine is turned over by a PDU via a rubber drive belt. Reducing friction and achieving near perfect balance in the crankshaft is therefore crucial, to ensure it always starts at ‘first kick’. The model was on display for two weeks at my place of work some while ago, operated by a push button by all and sundry, and, I’m glad to say, never faltered!
It makes quite a good demonstration piece to explain the four stroke cycle, as the timing and operation of the valve gear and ignition is correct, and it can be stopped and started at will, during or after each stroke. This must be one of the few Meccano models built to full size, and it has got me thinking about the possibilities for perhaps a vee-twin version, a four-cylinder water-cooled type for a car, or even a radial aero engine!
The model can be operated by push-button to rotate using a PDU. As a demonstration model of the workings of the four-stroke cycle it is quite effective and educational.