|Configuration||three-cylinder, six-piston opposed piston engine with rocker drive to a single crankshaft.|
|Displacement||3.261 litres (200 cu in)|
|Cylinder bore||3 1⁄4 inch (83 mm)|
|Piston stroke||4 inch (102 mm)|
|Oil system||Wet sump|
|Power output||105 brake horsepower (78 kW) at 2,400 rpm|
|Torque output||270 lb.ft at 1,200 rpm|
Rootes' intention for the engine was for it to fit under the QX "cab forward" design fitted to the R7 7ton truck released in 1948. This very advanced design had been built with the engine under the seat to allow three men to fit comfortably across the cab. The petrol version used a development of the Humber Super Snipe engine, lying at a 66 degree angle, and the opposed piston design of the TS3 was used so that it would fit in the same space.
It is often thought that "TS" in the engine's name derives from its Tilling-Stevens origins, a company acquired by Rootes in 1950 but this is incorrect. It stands for Two-stroke. Development of the engine started at the Humber plant at Stoke Aldermoor some four years before Rootes acquired Tilling-Stevens. After a single cylinder two stroke prototype (to test cylinder design) and two TS3 motors were built at Stoke Aldermoor to test the engine design, production moved in 1954 to the Tilling-Stevens plant in Maidstone, Kent, mainly because it had spare capacity.
The engine was unusual in being an opposed piston engine where each horizontal cylinder contains two pistons, one at each end, that move in opposition to each other. Even more unusually, both sets of pistons drove only a single crankshaft; most opposed piston engines have a separate crankshaft at each end of the cylinder. The TS3 engine used a single crankshaft beneath the cylinders, each piston driving it through a connecting rod, a rocker lever and a second connecting rod. The crankshaft had six crankpins and there were six rockers.
The engine was a two-stroke, compression-ignition diesel engine with uniflow-ported cylinders. Scavenging was performed by a Roots blower,[note 1] which was mounted on the front of the engine and driven by a long quill shaft from a chain drive at the rear of the engine. Although the engines gained a reputation for good performance, this quill shaft was somewhat prone to breaking if over-worked.
Data from 
- Type: Three cylinders, opposed pistons. Uniflow ports.
- Bore: 3 1⁄4 inch (83 mm)
- Stroke: 4 inch (102 mm)
- Displacement: 3.261 L (200 cu in)
- Power output: 105 bhp (78 kW) at 2,400 rpm
- Torque: 270 lb.ft at 1,200 rpm
- BMEP: 105 lb.sq.in
The TS3 was used in both the Commer and Karrier range of trucks. As the horizontal cylinders were lower than a vertical engine, the engine was mounted beneath the floor of the cab. The bonnet (hood) of the truck could be dispensed with, moving the windscreen and driver forward to give one of the first of the now common cab forward trucks.
Access for maintenance was generally good: a small hatch in the cab gave access to the oil and fuel filters, the injection pump and injectors. Connecting rods and pistons could be accessed from outside each side of the cab, behind removable doors, without removing the engine. As there was no camshaft or valves, this removed the usual need to access the cylinder head of a conventional engine. Even the blower could be replaced by first removing the radiator and working from the front. Only the crankshaft bearings required the engine block to be removed from the chassis.
The engine's distinctive exhaust bark was always apparent. It is often thought that this bark is where the popular name of "Knocker" for the TS3 comes from, but this is incorrect. The knocker name for the TS3 is a nickname coming from its extensive use in New Zealand and Australia. The later United Kingdom 3D215 and 3DD215 TS3 motors had the Clayton - Dewandre SC-6 compressor fitted with a harmonic damper which removed any timing gear clatter. Export versions of these TS3s had the larger Clayton Dewandre SC-9 compressor with no damper. Hence as the timing gear became worn over time, the export models produced that wonderful ʻknocker, knocker, knockerʻ sound at idle that is so well known in New Zealand and Australia but not present in the U.K. models
The TS3 was used in the Commer Avenger Marks II, III and IV PSV chassis, and also in a number of Integral models from John C. Beadle and Thomas Harrington Ltd from 1952-63. Initially these were a sales success, as they were more reliable and economical than the then-current diesel-engined variant of the Bedford SB, however the noise produced by the TS3 was not acceptable to tours operators and the higher body mounting compared with the SB required extra work for coachbuilders and made the Avenger more expensive than the Bedford. The last straw was in 1957 when Ford announced a PSV version of its Thames Trader, which could take an identical body to the SB and had a conventional six-cylinder diesel engine (which turned out to be quieter than either the TS3 or the Perkins R6 fitted to the SBO). From 1957 Commer Avenger sales began to dwindle. It's notable that Thomas Harrington Ltd never tooled updated versions of its Crusader body for the Avenger, although that is also perhaps due to the conservatism of the combination's sole customer Southdown Motor Services.
Rootes Group, Commer's parent company, entered into a partnership with Lister to market the engines as industrial stationary engines through a joint company Rootes-Lister Ltd. The venture was not a success for industrial engines, although some were sold as marine engines by Lister Blackstone Marine Ltd. Many of these marine engines survive today.
Sulzer ZG9 
There are very few similar engines. Opposed-piston diesel engines are rare enough at this size, the rocker lever arrangement was almost unheard of. Probably the only engine using a similar arrangement was the pre-war Sulzer ZG9. This was an opposed-piston engine with a choice of two, three and four cylinders (2ZG9, 3ZG9, 4ZG9); the two-cylinder version developed 120 bhp. Its layout was very similar to the Commer engines, but it used a piston scavenge pump rather than a Roots blower. This was mounted vertically above one rocker, driven by a bellcrank from the main rockers. This engine is sometimes cited as an inspiration for the Commer design.
Data from 
- Type: Two cylinders, four opposed pistons.
- Bore: 90 mm
- Stroke: 120 mm
- Power output: 50 PSe/36,77 kW at 1,500 rpm
- Gobron-Brillié - French cars, circa 1900, using opposed pistons driven
- Junkers Jumo 204 - an opposed-piston aircraft engine of the 1930s
- Napier Deltic - large multi-bank engine, with crankshafts shared between cylinder banks.
- Sulzer ZG9 - Swiss-made pre-war engine.
- Leyland L60 - tank engine, which Tilling-Stevens were involved in the design-of
- Roots is a different company to Rootes. The blower was actually made by Wade in Birmingham
- "Original brochure cover".
The Commer 'TS3' Diesel Engine. Precision built by the Rootes Group.
- Brian Vogt. "Commer TS3 Truck and Engine at the Greenock Aviation Museum".
"The TS3". Archived from the original on 2008-11-19. Retrieved 2009-01-26.
The engine was a direct injection, high-speed diesel engine with three horizontal cylinders, each containing two pistons, facing head-to-head. Each cylinder had specially designed ports to control the inlet of air and outlet of the exhaust which are controlled by the pistons. The pistons that control the inlet ports are known as the air pistons (left-hand side of the engine), the others being the exhaust pistons.
- Chapman, C.W. (1956). Modern High-Speed Oil Engines. Vol II (2nd ed.). Caxton. pp. 46–47.
"The TS3". Archived from the original on 2008-11-19. Retrieved 2009-01-26.
The TS3 was initially designed by Rootes Power Units Chief Engineer Eric W Coy (and under him, designers Bennett and Mileluski) at the Humber plant (Stoke-Aldermore) in 1948. It was designed solely to meet Rootes production planning requirements for an underfloor 105 hp diesel engine for the new forward- control Commer range of heavy trucks.
- "Rootes-Lister TS3: TS3 Horizontally Opposed Piston Engine Page 1". www.oldengine.org. Archived from the original on 2 May 2016. Retrieved 29 September 2016.
"The TS4 Prototype". Archived from the original on 2008-10-14. Retrieved 2009-01-26.
All the 14 prototype TS4s were test bed run initially. Eight were then put in trucks for road evaluation before going into production, running up to 1.2 million miles between them, trouble free. They were then pulled out and scrapped on instructions from Chrysler to protect Chrysler's joint venture in England with Cummins.
- Chapman, C.W. (1956). Modern High-Speed Oil Engines. Vol I (2nd ed.). Caxton. pp. 222–223.
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