The Ferret powerpack is a 129 brake horsepower fully waterproofed Rolls Royce B60 Mk 6A 4.2 litre straight-six with a dry sump.
The B60 is a member of a group of rationalised engines developed by Rolls Royce, and affectionately called ‘the B range’ by those involved in its development and manufacture. Since 1904, Royce had sought to ensure common components such as pistons, cylinders and valves were used, as far as possible, across a series of engine designs. A group of engineers at Rolls-Royce’s Clan Foundry in Belper led by W A Robotham completed development of the Meteor engine in 1943 and began work on a rationalised range of petrol engines to power a range of military vehicles, using a maximum of common parts. Manufacture of the B-series engine started at Rolls-Royce Crewe in 1947. The design aims were threefold: to provide the maximum power consistent with the minimum outside dimensions and weight; to use standardised components and so facilitate servicing and the stocking of spare parts; and to obtain the highest efficiency with low grade fuels.
The B range design is extremely reliable, just as the Army wanted. Full power is possible from virtually a cold start. The powerpack is extremely reliable: most still run well with regular maintenance after 50 years or more, and they can withstand rough usage and indifferent fuel quality without damage. These engines were required to run reliably and efficiently from -40°C to +50°C: in Arctic to Equitorial conditions as suited to all the theatres of Empire that the Army was required to serve.
The four-cylinder B40 was the smallest engine, with a swept volume capacity of 2,838 cc and a gross output of 80 bhp at 3750 rpm. Just over 19,000 were made in all, most powering the Austin Champ, the British answer to the Jeep that was superceded by the Landrover. Production of the B40 ceased in the early 1960s, whereas the other two engines continued for a further twenty years until the early 1980s.
The six-cylinder B60 was the mid-range engine, having a swept-volume capacity of 4,256 ccs., and a gross output of 130 bhp at 3750 rpm. The ‘0’ in the notation (e.g. B60) indicated that the bore was the standard 3.50 inches. About 14,500 of these engines were made: 9,395 Mk 6A versions for the Ferret. The ‘A’ notation signifies that the B60 engine has been adapted to fit the fluid flywheel. Besides powering the Ferret, they were also used in the Humber 1 ton truck. There were no military B61 engines (the ‘1’ notation (e.g. B61) indicating the larger bore of 3.75 inches) but these were fitted to Dennis civilian fire engines. These Rolls Royce-built engines their serial number (e.g. 865 3863) stamped into an identification plate on the top of the crankcase cover. Apart from the very early powerpacks, which were BSF, the majority of these B60 engines utilised UNF threads; a notice is cast into the rocker gear cover and prominently visible on top of the engine. These UNF engines incorporated a number of redesigned features (forged con rods; cast-iron cylinder head) to meet the demands of hard military use.
The large eight-cylinder B80 was produced in two configurations, the B80 having the same bore (3.50 ins.) & stroke (4.50 ins.) as the B40 and B60 engines with a swept volume of 5675 ccs, whilst the B81 had a bore size of 3.75 ins. (swept volume – 6516 ccs). The B80 had a gross output of 165bhp at 3750 rpm and the B81developed 195 bhp at 3750 rpm. About 4,700 B80 engines were produced and around 4,000 B81 engines. The B80 & B81 were used in the Alvis Saladin, and Saracen AFVs, the Stalwart load carrier, the Alvis Salamander airfield crash tender and the Thornycroft Nubian fire tender.
The compression ratio on the B60 is comparatively low; the 24v circuit delivers more electical power than a standard 12v system, therefore the battery does not need to deliver a very high cranking power, making the Ferret easy to start on most occasions. I use 90 Ah batteries with CCAs of 700 and 950 amps. I lined the battery boxes with cut rubber car mats to keep them secure and electrically isolated to prevent shorting. An isolator switch prevents electrical items and the wiring leaking current thus totally draining the batteries. The Saracen had this switch fitted as standard, but not the earlier Ferret.
The fuel gauge is notoriously inaccurate on the Ferret. I always fill my tank once it has gone below 1/4 full, and I’ve never had the need to switch over from the main to the reserve tank. Once, when the Ferret had been garaged for a few months, it would not start. My brother removed the air breather pipe, loosened the carburettor banjo nut, fixed an electric pump to the pipe (a good foot pump will also do) and pushed petrol through the system. We also checked the idling speed and that the banjos and seals were good on the Volkes petrol filter inside the Ferret. You don’t want air to be drawn in (or petrol to leak!) at this point.
In April 1989 Rolls Royce issued a service bulletin guidance stating that Lead free (unleaded) 95 RON and low Lead 97 RON fuel can be used in B 60 engines, and will have no detrimental effects on the exhaust valves or valve seats. If you know which Rolls Royce engine technical drawing you require, it can be downloaded from the International Club for Rolls Royce and Bentley enthusiasts.
Reference: Pat Ware (1995) In National Service: Rolls-Royce ‘B Series’ Engine in British Military Vehicles Warehouse Publications, ISBN = 978-095255-630-5