The O.600 engine got its identification from its displacement in cubic inches (US technical influence during WWII led to British commercial vehicle makers using Imperial dimensions until the late 1960s). The ‘O’ stood for oil engine - a British engineering term for compression-ignition engines, (rather than ‘diesel’, derived from the German inventor Rudolf Diesel). The 600 cubic inch swept volume equates to 9.8-litres.
The O.600 had a 4 4/5inch bore and 5½ stroke. In its usual application, the engine was rated at 125bhp at 1,800rpm, with peak torque of 410lbft at only 900rpm. In coach applications it was uprated to 130bhp at 2,200rpm This output meant that the engine was under-stressed, capable of giving lively, yet economic performance, with unprecedented (and it seems) unsurpassed ability to run hundreds of thousands of miles between overhauls. A major structural feature of the O.600 was the dry-liner cylinder block and crank-case which was a single cast unit. This was the first UK production heavy vehicle engine to feature this.
The O.600 is a six-cylinder direct-injection pushrod overhead valve unit. The cylinder head is split into two, with each head and gasket unit covering three-cylinders. Other important features designed to enhance reliability are a gear-driven camshaft, mounted lower in the block; a nitride crankshaft running in strip-bearings and chromium-plated piston-rings.
Over the years this engine had many modifications. In 1960 Leyland launched the Power-Plus version, with spheroidal combustion chamber cavities which gave more power and greater fuel efficiency.
From 1946 the O.600 engine was first fitted in Leyland truck chassis (Beaver, Hippo, Octopus, Steer, etc.) and from 1947 into PS2 Tiger (single deck) and PD2 Titan (double deck) bus chassis.
In 1947 the horizontal O.600 was developed. Laid on its side the engine is 1foot 10inches high. The main difference from the vertical model was a redesigned sump, longer engine oil filler spout and dipstick. Auxiliary units, (alternator and fuel pump), air intake and exhaust manifolds were relocated and slightly redesigned to be more accessible from the side.
The first horizontal O.600 engines went to Swedish bus maker Scania-Vabis in 1947. Leyland then introduced the horizontal O.600 to British customers at the 1948 Commercial Motor Show (Earls Court), where the new Leyland/MCW Olympic integral bus was fitted with this engine.
The horizontal O.600 engine was also used to power these Leyland bus and coach chassis: Tiger, Royal Tiger, Worldmaster, Titan, early Leopard’s, early Atlantean’s and some Panther’s.
Red&White use of Leyland O.600 engines
Red&White had taken an early batch of 52 Leyland Royal Tiger saloons in 1950 with the horizontal O.600 engine. They were obviously impressed with their performance on arduous hilly South Wales valleys routes, as when these buses came up for replacement in 1967 Red&White ordered 21 Bristol RESL’s with Leyland O.600 engines. One of these buses LAX 101E survives in preservation.
Later in 1967 the company bought 5 RELL’s with O.600 engines. And in 1968 Red&White ordered 10 Bristol RELH coaches (including our OAX 9F) and 20 RELL buses all with Leyland O.600 engines. Finally, in 1968 it took delivery of another 11 RELH’s with 600 engines.
Red&White (and Cumberland Motor Services) were the only two companies to buy Bristol RE’s with the Leyland O.600 engine. R&W took a total of 67 RE’s with this power unit. All other bus operators that bought REs powered by a Leyland engine, opted for the larger, slightly more powerful Leyland O.680 unit.
By the mid 1970’s Red&White did recognise that the O.600 engine was a bit underpowered for coach work and introduced a programme to retro-fit all its Bristol RELH’s with the Leyland O.680 engine. However, our coach (due to its low mileage) never gained the larger Leyland engine. And so it is now the only surviving Bristol RELH fitted and running with a Leyland O.600 diesel engine.
How do we know OAX 9F has a Leyland O.600 engine?
The engine block has a large ‘600’ cast in it, whereas all 680 engines have ‘11.1’ cast in them (representing 11.1 litres).
Much of the technical information has been drawn from the ‘Leyland Bus Mk 2’ book by D. Jack (published May 1984).