The Heart of Many Dennis's - The Rolls Royce B80
From the early 50's to the 80's the heart of most petrol engined Dennis appliances was the Rolls Royce B series engine. The B60 (the six cylinder engine) was fitted to the smaller machines like the F8 and the B80 (8 cylinder engine) was fitted to the larger appliances like the Belfast ET (OZ9606) which has been the subject of recent discusion. The B40 (4 cylinder) engine completed the range but was never used by Dennis. All of these engines feature interchangeability of parts accros the range, making then particularly appealing for use by the armed forces.
The engine in the above picture is that belonging to OZ9607 the Belfast Dennis Metz TL. You will see the dual ignition coils which are selected from a switch on the dash panel. Only one at once is ever used, but this redundancy gave greater reliability. (It was almost a 'hangover' from earlier days when most appliances had selectable coil or magneto ignition. Mechanical and electrical fuel pumps are present again selctable by a changeover switch).
B80's and the later slightly improved B81, are very soft engines and can easily be started by a light pull on the starting handle. They are slightly unusual in that they have overhead inlet valves but side exhaust valves. Their only weakness is that the cylinder bores are quite close together so that the head gasket can blow through between two adjacent cylinders. Unless caught soon enough this leads to a a chnnel being burnt into the cylinder head which then leads to quite an expensive repair. The later B81 will drop straight onto a B80 block and this is the configuration shown in the photograph.
Picture added on 09 January 2009