Stationary Engine Kits

Anthony Mount Models

Boulton and Watt Bellcrank Engine 1802

The Bellcrank engine was introduced by Boulton and Watt in 1802. The design was formulated by William Murdock and the Soho foundry manager a Mr Southern. The aim was to supply a small self contained engine, to the smaller manufacturer who could not afford a house built beam engine. The design was called a Bellcrank on account of the shape of the rocking leavers. These resembled the leavers that transferred the pull of the ropes in a bell tower to the bells.

The design was in production from 1797 until 1806, when Boulton and Watt introduced their small self contained beam engine mounted on a cast iron cistern. From my research all the engines seemed to vary slightly one from another. The earliest engines were filled with a form of drop valve. Then came the long D valve, followed by the slide valve. The model is based on one from 1802 and this had a long D valve.

The drive to the valve is interesting. Bolted to the flywheel is an eccentric ring. A forked end of a lever pivoted on the cylinder, fits into the ring. As the flywheel revolves the lever is raised and lowered. On the other end of the pivot shaft is another lever. This lever fits into a slot in a shaft that slides up and down while attached to the steam chest. The sliding shaft has a link at the top which attaches to the valve rod.

The base of the engine is a cistern, inside there is a condensing tank. The cylinder is also mounted on the cistern as are the crankshaft bearings. The flywheel is carried on a separate shaft mounted in its own bearings.

The model is to a scale of 1 3/16” to 1ft, which gives a flywheel of 9” (225mm) diameter. Castings are for flywheel, cam ring, cistern, condenser, cylinder, covers and steamchest. There are 26 drawings and a parts list in the set, all are of A4 size. The drawings have both metric and imperial dimensions.

Construction is quite straight forward, and can be carried out on a 3 ½” lathe. A drill and mill will make things a bit easier of course. One variation from the norm is the long D valve, which is not self sealing like a traditional slide valve. It can be viewed like an inside admission piston valve. Except that the heads are not circular but D shaped. The valve is hollow and exhaust from the top of the cylinder passes down through the valve to reach the condenser.

Serialisation of the model began in Engineering In Miniature July 1993 and ended in June 1994. Castings and drawings are available from Bruce Engineering and their address is.