Commer

The Commer brand started in 1926, when Humber took over Commercial Cars Limited that had produced its first ‘Commer Cars’ truck, a three-ton RC type in 1907, followed by other truck and bus models.  

By the time Humber took over the ailing Commer Cars business in 1925, model development had stalled.

New Humber-Commer models of 1928 were 11/2-ton and a 41/2-ton trucks and four bus chassis in four- or six-wheel configurations and forward or conventional control.

Humber and Commer became part of the Rootes Group in 1928. Rootes had already swept up a number of smaller car makers, including Hillman, Singer, Talbot and Sunbeam.

In 1934 Rootes took over Karrier Motors that dated back to 1904. The Commer and Karrier brands were rationalised and Karrier was used on smaller trucks and vans, while Commer branded heavier trucks. 

The N-series trucks and PN bus were introduced in 1935 and went on to serve with the British armed forces in World War II. There was choice of 3.2-litre and 4.1-litre, six-cylinder petrol engines and the Perkins Leopard diesel.

The range was numbered N1 to N6, denoting their approximate weight capacities in tons.

The oddly-named Commer ‘Superpoise’ Q-series was introduced in 1939, rated at 1½ to six tons, powered by six-cylinder petrol or Perkins diesel engines.

Commer, like all other British manufacturers made a full range of military vehicles for  the war effort. 

A new Superpoise ‘T’ range was introduced in 1955 with 2 ton to 5 ton payloads.

The famous ‘knocker’

From 1954, some Commer and Karrier trucks were fitted with the iconic Rootes TS3, two-stroke, opposed-piston diesel engine. This engine had around half the weight and half the displacement of similar-output engines and could be installed easily underfloor, doing away with the need for a bonnet, or an engine tunnel inside the cab.

At a time when head-sealing issues were a massive problem for engineers, the ‘headless’, opposed-piston TS3 was a godsend.

Developed by a tiny team of four engineers, headed by Eric Coy, this 3.25-litre, three-cylinder, six-piston engine was revolutionary. Being a three-cylinder two-stroke, it was given the moniker ‘TS3’.

There’s a commonly held – but incorrect – belief that the engine was designed by the engineering company, Tilling Stevens – possibly because of the ‘TS’ nomenclature. Tilling Stevens was taken over by Rootes in 1951, mainly for its additional manufacturing space and TS3s were produced there. The company’s most popular bus chassis had used the model number, ‘TS3’, for years, but why would the company cause deliberate confusion by giving its new engine that identical nomenclature?

Also, there were already two Rootes-team-designed running prototypes of what became the production TS3 when Tilling Stevens became absorbed into the Rootes Group. The TS3 development had begun immediately after WWII.

For more info on the Rootes TS3, check out our story on Two-Stroke Diesels in the Truck Features section of this website. More reading includes: The Commer Story by Geoff Carverhill, published by Crowood Press in 2002 and in his subsequent books: The Rootes Story – Part 1 / (Crowood Books 2018) and Part 2 – The Chrysler Years (Crowood Books 2023). Another authority is Opposed Piston Engines: Evolution, Design and Use by Martin Flint and Jean Pierre Pirault.

Being a two-stroke the Commer TS3 required Sulzer-style supercharging, via a Roots (not Rootes) blower to induce air for the power stroke, while simultaneously forcing out exhaust gases.

Most opposed piston engine designs have two crankshafts that are geared together, to drive an output shaft, but the TS3 engine used a single crankshaft beneath the cylinders, with each piston driving it via a primary connecting rod, a rocker-shaft-mounted bell-crank and a second connecting rod. 

The supercharger was shaft-driven from the rear of the engine, via the timing gears. Early TS3s had chain-driven injection pumps, but later models employed a zero-maintenance gear train.

The 3.25 litre engine developed 90hp (67kW), with 270lbft (360Nm) of torque at launch and was later coaxed to produce 117bhp, then 140hp.

Displacement of the TS3 was increased to an optional 3.5 litres in 1964, following increased legal axle weights in the UK that prompted the Commer Maxiload series. Three engine outputs were available: the 3.25-litre 3D-199 standard torque rating (D code in the model designation on the truck build plate) of 100bhp; the 3.25-litre 3DA-199 High Torque rating (E code in the model designation) of 117bhp and the 3.5-litre 3D-215 rating of 135bhp.

With turbocharging, the TS3 went on to produce 160hp, but these development engines were less reliable.

Interestingly, the nickname ‘knocker’ was applied only to Australian and NZ export engines that had a larger braking-system air compressor that lacked a harmonic damper. When the compressor gear train became worn the engine emitted a characteristic ‘knocking’ sound at idle.

A TS4, four-cylinder, four-litre, eight-piston engine was at the pre-production stage when the Rootes Group fell into Chrysler’s hands in 1968.  Production of the TS3 ceased in 1972 and the TS4 project was abandoned in favour of conventional, in-line engines.

Chrysler had the Commer name dropped from the truck range and replaced it with ‘Dodge’. 

A light duty Commer FC van was introduced in 1960 and renamed the PB in 1967, and the SpaceVan in 1974.