For a period of just under 20 years (1955-1974), Allis-Chalmers produced one of the most popular small track type tractors ever built, the model HD-6. By Richard Campbell.
It was not the first successful small crawler that Allis-Chalmers had manufactured and in fact replaced another remarkably popular machine, the model HD-5, which had been the first of Allis-Chalmers’ post WWII tractors to be introduced, in 1946.
Following Allis-Chalmers’ acquisition of the Buda Engine Company in 1953, the company set out to design replacements for its existing track type tractors that were all powered by GM (General Motors) diesels.
The HD-5 had been powered by a 2-cylinder, 38 horsepower GM 2-71 and was a remarkably versatile little machine, so Allis-Chalmers management had high hopes for the new HD-6.
Initially powered by a 4-cylinder Allis-Chalmers (Buda) model D-344 engine rated at 57 flywheel horsepower, the new machine was immediately embraced by contractors, loggers and the agricultural sector alike and by 1963, when Allis-Chalmers began to upgrade its track type tractor line, it had sold over 13,000 examples of the HD-6!
A change to the fuel injection system was made in 1963, replacing the original Buda Lanova type fuel injection pump with a Bosch inspired design that metered the fuel more accurately resulting in more horsepower, reduced fuel consumption, easier starting and cleaner burning.
This engine was known as the 6000 series and it produced 52 horsepower in naturally aspirated form.
As the HD-6 evolved there were many versions of the machine to cater for different customer requirements and conditions, and like the HD-6’s biggest competitor, the Caterpillar D4, the HD-6 was available in two track gauges – 44 inch and 60 inch.
To gain a better understanding of these different HD-6s, as Allis-Chalmers did not always differentiate well between models creating some confusion, here is a short summary of the main models.
From 1955 thru to 1963:
HD-6 60” gauge, 4-roller frame, manual transmission, 57 hp
HD-6B 60” gauge, 5-roller frame, manual transmission, 66 hp
HD-6A 44” gauge, 4-roller frame, manual transmission, 66 hp
HD-6E 60” gauge, 5-roller frame, manual transmission, 66 hp
HD-6PS 60” gauge, 5-roller frame, powershift transmission, 72 hp
All of the above machines were powered by the D-344 diesel.
From 1963 onwards the models were:
HD-6B 60” gauge, 4-roller frame, manual transmission, 69 hp
HD-6A 44” gauge, 4-roller frame, manual transmission, 69 hp, (discontinued 1964)
HD-6E 60” gauge, 5-roller frame, manual transmission, 69 hp
HD-6EP 60” gauge, 5-roller frame, powershift transmission, 75 hp
These were all powered by the model 6000 diesel.
As can be seen from the chart, the 60” gauge model was by far the most popular size.
Although we are focusing on the HD-6 dozer in this feature, mention must also be made of the track type loader variant that was based on the HD-6, the model HD-6G. This was also a very highly regarded machine and will feature in a future article.
Just to muddy the waters even further, there was also an HD-6AG model, built specifically for agricultural purposes with a 60” gauge, 5-roller frame and 90 horsepower at its disposal.
Allis-Chalmers pulled the plug on HD-6 production not long after its final integration with Fiat, but the machine left a lasting legacy and many are still in use although its ranks are thinning a bit due to the scarcity of parts.
It was replaced in the Fiat-Allis line by the model 8 (later FD-8).
The Allis-Chalmers HD-6 described
Of conventional track type tractor layout, the HD-6E (for this review) was powered by an Allis-Chalmers 6000 series diesel engine rated at 69 flywheel horsepower and connected, via a multiple disc oil clutch, to a 5-speed sliding gear manual transmission, which was also manufactured by Allis-Chalmers.
Gear ranges from 1.5 to 5.8 miles per hour were standard with a 2-speed reverse.
A 5-roller track frame with 1 carrier roller per side was pinned through the rear final drive housing and joined at the front by an equaliser bar, which allowed approximately 28 degrees of oscillation.
The HD-6E was what could be called the “deluxe” version as it had power assisted steering clutches and brakes, which made it a pleasure to operate.
Unusually for a tractor of this size, the HD-6E had double reduction final drives, a feature that undoubtedly added to the machine’s longevity.
The operator’s area was conventional in layout and quite compact with all the levers falling nicely to hand. A small instrument panel was slightly offset to the right hand side and a deeply cushioned seat was provided for the operator. Some models of the HD-6E had adjustable seating but this was usually an optional extra on other versions of the machine.
One of the other nice features of the HD-6 was the excellent visibility it provided to both front and rear. This was built in from the very first production machines with a tapered hood, sloping fuel tank and operator seat placement.
Just about anything could be mounted on, pushed in front of, or drawn behind an HD-6! By the time the machine went into full production in 1955, Allis-Chalmers had purchased one of its main attachment suppliers (Baker) and so had access to all the ‘goodies’ necessary to equip the machine.
Lighting sets, canopies, cabs (rare in NZ), agricultural conversion packages were all provided in-house to equip the HD-6 for customer needs.
Paccar’s Carco division manufactured a nice little winch that could be fitted if required.
The New Zealand connection
Allis-Chalmers HD-6s were very popular in New Zealand and were sold from one end of the country to the other. Exact importation records are unavailable as neither of the agents selling the machine (CablePrice in the North Island and Andrews & Bevan in the South Island) have kept any records.
The HD-6 was particularly popular in hill country and in logging where many owners believed it was superior to the Caterpillar D4 due to the HD-6’s lower centre of gravity.
Many operators have told the author that it just clung to the sides of hills “like a magnet” and that they felt very safe behind the controls.
The ‘average’ New Zealand-delivered HD-6 was fitted with a bush canopy, hydraulic angle blade and Carco winch on the back. Ripper equipped machines were not too common but there were quite a few delivered set up to tow small scrapers such as the CPC-6, Caterpillar No.40, Blaw-Knox BK60 and Onions 4-6.
To tow the latter scraper, the machine needed to be fitted with a suitable cable control (PCU).
For the model collector
A bleak outlook as no manufacturer has to date produced a model of the HD-6.
This is a bit of a travesty really considering the number of these machines that were manufactured.
There is a model of the machine’s predecessor, the HD-5, but it is old, inaccurate, expensive and to a very odd scale.
Brief Specifications: 1969 Allis-Chalmers HD-6E
Engine: Allis-Chalmers 6000 series, 4-cylinder, naturally aspirated diesel engine rated at 69 flywheel horsepower @ 1800 rpm
Transmission: Allis-Chalmers 5-speed sliding gear, manual
Clutch: Multiple plate, oil cooled
Steering: Hydraulically assisted multiple clutch
Brakes: Hydraulically assisted contracting band
Track gauge: 60 inch
Track frame: 5-roller
Tracks: 37-section, sealed
Standard track shoe: 13 inch
Operating weight: 6.5 tons (bare)