1953 Kenworth Model 721: Review

Name: 1953 Kenworth Model 721: Review
Brand: Kenworth

Beautifully restored classic with a rare and historic petrol engine

We’d been told about Zell’s impressive line up of Kenworth trucks and had made the overnight journey to Collarenebri in north-west New South Wales to check out their latest Kenworth. Shortly after we arrived, Gavin and bother Wayne had promised to show us a real classic Kenworth when we returned from a run in their T909 hauling three tippers of grain in a triple road-train configuration.

When Gavin and Wayne opened the doors I was speechless, there in shed stood an immaculately restored 1953 Kenworth, Model-721.

“We’ll bring it out so you can get a better look and some photos,” Gavin said. Moments later, the old Kenworth fired into life, and the slow deep idle of the big-bore Hall-Scott petrol engine sounded sweet too. Then with a slight creak of the clutch and gentle clunk as first gear was engaged, the old Kenworth slowly rolled out into the late afternoon sunlight.

This 1953 Kenworth, according to the manufacturer’s plate, had a top speed of 62 miles per hour, which was pretty damn quick for the period. But it needed to be, because the old classic started life as a fire truck for the Seattle Fire Department.

According to Kenworth’s book, The First Seventy Five Years, Kenworth remained aggressive in its marketing and found new opportunities commencing the production of fire trucks in 1932 to combat the depression and an uncertain future. It was a bold move yet one that paid off. Since the rest of the truck market seemed set on building standardised trucks, Kenworth’s unique ability to custom build trucks to suit a customer’s application gave them the upper hand when it came to the fire truck market segment. It is said that each fire chief had his own ideas regarding what he wanted on his fire truck, and Kenworth was able to accommodate the specific wishes from the various fire stations.

Kenworth's Murray Aitken is quoted as saying: "Every fire chief felt that he was the world's leading designer of fire trucks, and he wanted some of his ideas incorporated into the fire trucks. As a result, there was a market that Kenworth could satisfy that some of the other manufacturers weren't able to comply with."

The Hall-Scott engine in this Model-721 was an advanced designed for the period and very popular in fire truck specified models, from the 1950s through to the 1960s. In fact, in one report it’s written that the Los Angeles City and County fire departments bought hundreds of them.

These Hall-Scott engines, known as the model 400 have a 5¾ inch (146mm) bore with a 7 inch (177.8mm) stoke, which gave them a capacity of 1091 cubic inches or roughly 18-litres. To put this in perspective, this engine is two-litres bigger than a current Cummins Signature engine. Needless to say as a petrol engine, in today’s economic climate it would be a rather expensive engine to keep running on a regular basis.

For a motor developed in the 1940s this particular model engine, boasted many advanced features including an overhead camshaft, hemi-head, twin ignition system with twin points and coils, which made them very attractive to the fire departments.

They produced roughly 300 horsepower (224kW) and developed approximately 925 ft/lbs (1254Nm) of torque, which according to one old friend who drove one was: “That much power it’d blow the back off the trees”.

The transmission is a Spicer 8421 five-speed and the rear axle is a Rockwell R100 with hydraulic brakes.

In fact, back in the day, owners and drivers reported that these Hall-Scott engines produced tremendous power and ran smoothly for many years, However, many added they could not pass a petrol station without topping up their fuel tanks.

Hall-Scott Engine History

The history of the Hall-Scott engine building enterprise dates back to the early twentieth century. When two young Californians, Elbert J. Hall and Bert C. Scott, founded the legendary Hall-Scott engine company by producing gasoline powered rail cars. The duo then went on to build motorcars (self propelled rail carriages) from 1910 to 1921 before moving on to aircraft and marine engines, where they enjoyed their greatest success. Over the course of the next fifty years the company earned a reputation for building outstanding engines.

By the outbreak of World War I, E.J. Hall and his company had established international reputations in air power. By then, Hall-Scott engines boasted high-tech features such as overhead camshafts and valves, hemispherical and cross-flow cylinder heads, interchangeable parts between models, and aluminum pistons and crankcases. In fact, these features became part of every production Hall-Scott engine sold after that period.

A hemispherical head ("hemi-head") gives an engine an efficient combustion chamber with minimal heat loss to the head, however in most cases this design only allows for two large valves. Because the intake and exhaust valves lie on opposite sides of the chamber these heads generally incorporate a "cross-flow" head design.

The model 400 engines were first produced from 1940 however with the USA entering the war in December 1941, Hall-Scott had all but ceased civilian production, concentrating on military applications. Over 1700 Hall-Scott 400 motors were used in the US army’s massive tow truck the M26 during the war years.

Over the next decade the model 400 could produce up to 450hp and over 1000 lb/ft torque, however finding driveline components strong enough to handle so much power was a challenge. Choices were narrowed to either Timken or Spicer who had strong enough components.

With the end of World War II, the model 400 engine had a earned itself an enviable reputation along with a proven record for performance and reliability combined with very favourable press reports with engines ranging from 107 to 900hp, the largest a supercharged V12. Yet it was the model 400 that proved the big seller and quickly established a name for itself in the trucking industry as it could out-pull just about anything on the road.

Hall-Scott sponsored articles in truck magazines from 1945 with the title Save Eight Hours on the LA to Salt Lake City Run. Sales began to sore to 749 units in 1947, but that was the peak year and from then on sales began to drop off.

In the USA, petrol was cheap, power and speed were king. Hall-Scott were big petrol motor makers and capitalised on this need for speed. In fact they were one of the last petrol engine builders to hold out against the diesel option.

At the time, the outcome was similar in Australia the International R190 and Dodges of the day were a couple of the more popular petrol trucks.

Although by the early Sixties, diesel-powered trucks from the UK were beginning to make an entrance into the Australian truck market, nevertheless their performance generally did not instill confidence with Australian operators. Typically they were very low geared with most only managing a top speed of 25mph compared to American petrol-powered trucks that would do twice that speed.

As time went on many operators began to repower these trucks with the Perkins 6354 diesel, which would pull a tandem trailer, and by the end of the 1960s diesel had over taken the petrol engine as the preferred power plant in the larger trucks.

In 1954, Hall-Scott had invested heavily in the development of the new lightweight petrol engine dubbed the Model 590 that produced 250hp and 500lbs/ft of torque, which ran out to 2800rpm. However this engine did little to improve sales like management had hoped.

However by the late Sixties, the diesel engine's lower fuel consumption and increased power spelled doom for the petrol-engine market in heavy trucks and equipment, regardless of manufacturer.

According to a 1957 report, mechanics and drivers preferred the Hall-Scott engines over the diesel alternatives, however trucking company owners could not afford to run them with fuel consumption of only 2 to 3 mpg (141.2L/100kms) on long-haul runs when diesel-powered trucks were running at less than half the fuel cost.

Hall-Scott had no capital to invest in the development of a diesel engine and the company was sold to Hercules in 1958 for a reported $1.8 million and so ended the 60-year era of the legendary Hall-Scott engines.

Gavin and Wayne’s father Bill stumbled on the old Kenworth some years back, and with the help of Sydney-based Kent Truck Repairs organised its restoration. These days, this old Classic Kenworth spends its time lazing on the farm and putting in the odd appearance for a photo-shoot every once in a while.

Specifications:

Model: Kenworth 721

Engine: Hall-Scott 1091-G1

Bore: 5¾ inch (146mm)

Stroke: 7 inch (177.8mm)

Sparkplug Gap: 0.020”

Horsepower: 300hp (224)kW @2100rpm

Torque: 925lb/ft (1254Nm) @ 1500rpm

Gearbox: Spicer 8421 five-speed

Air Cleaner: Oil bath

Fuel Filter: Inline

Electrical: 12 volt