Jensen Jen-Tug Lorry

Introduction

We doubt many would know that Jensen Motors Ltd., of West Bromwich, introduced a six-wheeled outfit known as the Jen-Tug after World War 2. It was, to say the least, an interesting machine designed to perform work comparable to that of a horsed vehicle, although its robust construction was probably an invitation to some operators to overload it.

Its payload capacity was given (at the time) as between 30 cwt. and 40 cwt., a load with which it dealt easily and with a degree of quiet running that was particularly noteworthy. Pressed steel channel-section side members were employed for the tractor frame, which was inswept towards the rear at a point abreast of the gearbox. These members were 5 inches deep and were suitably cross-braced and fully gusseted at the corners.

An outstanding feature of the design was the employment of a sub-frame, on which was mounted the complete power unit and transmission. It was possible to remove the whole unit, from radiator to rear axle, merely by taking out the bolt in a Silent-bloc mounting, and disconnecting engine and gear controls, fuel connection, and the wiring to the engine. The power unit was a Ford 10 h.p. petrol engine, which gave 30.1 b.h.p. at 4,000 r.p.m., and produced a torque of 46.4 lb./ft. at 2,400 r.p.m. This engine had a bore of 2.5 in. and a stroke of 3.64 in., the swept volume thus being 71.55 cu. in. (1,168 c.c.)

The cooling water circulated on the thermo-syphon principle, an 11 in. diameter, four-bladed fan driven by a V-belt, inducing the draught through a large capacity radiator. The latter was mounted amidships behind the cab. In order to obtain the necessary electrical output at a moderate speed a 4.5 in. dynamo was fitted and was belt-driven, in a triangulated arrangement with the fan. The Solex down-draught carburettor incorporated an atmospheric governor which controlled the engine speed to a maximum of 2,750 r.p.m. Petrol was fed to the engine by a mechanical pump, the petrol tank, of 8.5 gallons capacity, being mounted forward of the radiator beneath the driving seat.

The gearbox which was also of Ford make and built as a unit with the engine provided three forward speeds and a reverse, second and third gears being of the synchromesh type. The basic ratios were 3.40, 1.96 and 1.00 to 1 forward and 4.45 to 1 reverse. With a rear axle ratio of 11.66 to 1 the overall gear ratios were thus 39.68, 22.85 and 11.66 to 1 forward and 51.9 to 1 reverse. The gear change lever was brought to a position just below the steering wheel where it came within convenient reach of the left hand. The drive from the engine to the gearbox was by a single plate dry clutch, 7.375 in. diameter, the total friction area being 55.62 sq. in., with a plate pressure of 450 lb. as a maximum.

A short, stiff shaft, provided with needle-roller-type Hardy Spicer couplings, took the drive from the gearbox to an underslung worm-driven rear axle, the casting of which was a one-piece malleable casting. The worm and worm-wheel assembly was arranged as a separately detachable unit, the dropping of the axle casing base, and the withdrawal of the drive shaft, permitting its removal. The engine and transmission were set over to the off-side of the chassis so that the rear axle drive housing would clear the ramp of the coupling gear.

Jen-Tug Design

Girling brakes were employed on both the tractor and trailer, all the wheel drums being 11 in. diameter by 11 in. wide. As the breaking technique on an outfit of this type required maximum retardation on the trailer wheels, the trailer brakes were of the two leading shoe type, with normal leading and trailing shoes in the tractor drums.

The ratio of the steering gear, which was by Cam Gears Ltd., was 16 to 1, and a refinement in the steerage linkage was found in the use of Thompson self-adjusting ball-joints to the drag link and track rods. A drop forging was used for the front axle with phosphor bronze bushes for the king pins; the turning circle was about 22 ft.

Wheels of the three-piece detachable type, with locking rings, were used on both tractor and trailer, and were equipped with 25 in. by 6 in. tyres. In the construction of the cab light alloys were used for panelling and sheet-metal work. The cab was notable for its roominess, the degree of visibility it provided, and, what was also important, operators could simply step in or out of it without hindrance, as its floor was but 1 ft. 9.5 in. from ground level.

It had an adjustable back rest so that, irrespective of the operators stature, a driver could find the most comfortable position in a few seconds. All controls being mounted on the chassis, cab removal was considerably simplified. The trailer itself had a 13 ft platform; measured over the shock rails the width was 6 ft. 6 in. The turntable incorporated two non-retracting vertical arms with wheels at the lower end to enable the trailer to be manoeuvred when detached from the tractor.

The Jen-Tug Coupling

The coupling was of Jensen design and had a single inclined ramp, with deep flanged guide wheels on the trailer. When the flanged-wheel shaft entered the yokes on the trailer coupler, two horizontally disposed hooks enveloped it, and held it securely in position.

The operation of coupling up was, of course, entirely automatic, and there was an overload device which enabled the two units to be coupled should the operative leave the hooks in the locked position. In order to reduce rattle, and consequent wear to a minimum, buffer springs were incorporated in the coupling gear, their effect being to keep the relative components up to one another when the outfit was in operation.

Equipped with two trailers the Jen-Tug could work between say a factory and wharf, leave a trailer for unloading while travelling back to collect the trailer being loaded. Economical and easy to handle, the Jen-Tug had a multitude of uses.

Jen-Tug Specifications:

• Engine: Ford 10 h.p., four cylinders, side valves, bore 63.5 m.m. by stroke 92.5 m.m.; capacity 1172 c.c. (71.55 cu. in.) 30.1 b.h.p. at 4,000 r.p.m., 46.4 lb./ft torque at 2,400 r.p.m.
  • Compression ratio 6.16:1. Solex carburetter fitted witk cold starting device and atmospheric governor, controlling speed at 2,750 r.p.m., 8£ gallon fuel tank.
  • Lubrication - Pressure feed by gear type pump to main, connecting rod and camshaft bearings, constant overflow to timing case, splash feed to other moving parts.
  • Cooling - Thermostatically controlled to 75 deg. C. assisted by four-bladed fan (Vee-belt driven) and radiator of ample capacity incorporating pressure boost of 5 lb. sq. in.
  • Circulation - thermo-syphon.
• Transmission: Clutch—single dry plate, ball-bearing release, 7.375 in. diameter. Total friction area 53.60 sq. in. Gearbox - Three speeds forward and one reverse, synchromesh on second and top, spur gears on first and reverse. Remote gear change control, lever under steering wheel. Ratios—1st, 3.40, 2nd, 1.96, top, 1.00, reverse, 4.45 to 1. Open propeller shaft, Hardy Spicer needle roller bearings.
• Axles: Rear, fully floating, underslung worm, 5 in. worm gear centres, ratios: 11.66:1. Front: drop forging, I section beam. King pins working in phosphor bronze bushes and thrusts. Hubs mounted on taper roller bearings.
• Suspension: Tractor - front semi-elliptic, rear end sliding. Rear springs, quarter-elliptic with sliding end working on radiused seating to give progressive action. Trailer - semi-elliptic, rear end sliding, laminated spring blades graded to give progressive action. All spring eyes fitted with oilless bushes.
• Brakes: Tractor - "Girling" 11 in. x 1J in., normal trailing and leading dhoes hydraulically operated to all four wheels, plus mechanical operation to rear Wheel:. Trailer - "Girling" 11 in. x 1$ in. two leading shoes. A separate parking brake is mounted at the front end of the chassis.
• Steering: "Cam Gears" unit Fore and aft drag link. Ratio of unit 16:1. 17J in. steering wheel diameter.
• Wheels & Tyres: 3.75 x 13 three-piece with detachable rim, on all three axles, fitted with 25 in. x 6 in. tyres.
  Dimensions: Overall length: 19 ft 8| in.; max. width, 6 ft. 6 in. over check rails. Platform height (laden), 3 ft. 2i in.; track, front axle, 51J in.; trailer axle 62| in.; Intermediate axle, 29i in. Wheelbase tractor, 70J in. Wheelbase trailer, 81J in. (coupled). Weight (unladen), approx. 29 cwt Pay load. 30-40 cwt. Turning circle, approx. 22 ft.
• Coupling: Coupling of patented design comprising a single inclined ramp attached to the tractor, which engages a deep flanged wheel . on the trailer fore-carriage.