Caterpillardual axle

The Caterpillar 641 single engine scraper

Up until 1962 Caterpillar had not really ventured into the world of large scrapers other than in its line of cable operated towed models. However, behind the scenes Caterpillar had been developing a whole new range of motor scrapers which were to be known as the ‘600’ series. BY RICHARD CAMPBELL.

Caterpillar had made good progress with the DW10, DW15, DW20 and DW21 motor scrapers, but these machines were becoming outdated due to advances in hydraulic technology and the resultant shift away from cable controls.

A taste of things to come arrived in 1959 with the Cat 619, which featured planetary final drives and a power shift transmission – both items were not available in the DW range. However the 619 still had a cable operated scraper.

Our subject this month is a member of the 600 family, the Caterpillar 641.

Rated at 28 cubic yards struck and 38 cubic yards heaped the Caterpillar 641 was a quantum leap in Cat scraper design. Released in 1962 along with the models 630A, 631A, 632, 650, 651, 657, 660 and 666 the 641 sat roughly in the middle of the range capacity-wise.

In order to take best advantage of the new machine’s capabilities, Caterpillar had also developed a new range of engines and transmissions to cope with the higher horsepower requirements that had become necessary to move these big beasts around.

The power plant chosen for the 641 was the Caterpillar D346. This was a 60 degree, V8 turbocharged diesel engine, rated at 450 horsepower at 1900 rpm. This was mated to a nine-speed Caterpillar full powershift, barrel type, planetary transmission that incorporated a downshift inhibitor to prevent the engine over speeding.

In top range the 641 could get along at almost 30 miles per hour (50 km/h), which was a very reasonable speed for such a large machine.

In 1965 engine output was increased to 500 flywheel horsepower.

For stopping the Cat 641 used air operated shoe type brakes, supplemented by a hydraulic retarder to extend brake shoe life. This was a standard factory fitted item.

Steering was via two double acting cylinders connected to torque multiplying linkages mounted high on the gooseneck hitch.

Compared to earlier Caterpillar motor scrapers, the 641 operator was quite well looked after. Visibility was very good to most quadrants apart from the direct right, which was partially obscured by the large air cleaner assembly. Visibility to the cutting edge was good.

A deeply padded seat was positioned over the top of the left wheel well, and was provided with a hydraulic snubber. This however did little to iron out the rough riding characteristics of a two axle scraper.

A comprehensive set of instruments (including a rev. counter with a tell-tale) were provided on a split instrument panel on either side of the steering column.

A steering brake was provided to assist in controlling wheel slippage should the machine become stuck. (Later series machines had a foot operated differential lock to control unwanted wheel spin.)

Scraper operation was by three separate levers – one to raise and lower the bowl, one for raise and lower the apron, and the other controlled the ejector.

An optional attachment on earlier production machines was a synchronization switch, which lowered the apron when the bowl was raised to carrying height, thus saving the operator quite a few hand movements during an operating shift. This attachment later became standard equipment.

Optional equipment included a cab and full heating for colder climates.

As was stated previously, the 600 series was a completely new design for Caterpillar and nowhere was this more noticeable than in the design of the bowl.

This was all-hydraulically operated – not a hint of cable – and drew upon research and experience gained from the previous cable operated “lowbowl” scrapers. It was very modern in appearance.

Two double acting lift cylinders provided penetration force for the cutting edge and were fitted with check valves to prevent sudden bowl dropping in the event of a hose failure in the hydraulic circuit.

Also incorporated into the bowl cylinders was a quick drop function that allowed pump loading in difficult loading material, such as sand. It also worked very effectively as an emergency brake.

The apron was connected via a solid link to a lever arm which was operated by a double acting hydraulic cylinder buried in the gooseneck. This gave the apron some power to force its way through material in closing and was not dependant on weight of material carried in the apron to effect closure.

The ejector was powered by a single double acting cylinder and was fitted with a gate type spillguard.

In late 1963 Caterpillar offered an “extreme service” bowl for the 641 (and selected others in the 600 family) for use in severe loading conditions. This featured considerably more high analysis steel in all the wearing areas and, in the 641s case, added an extra 4000 pounds to the weight of the machine.

Along with the extra steel, thicker, heavier duty cutting edges were also supplied.

It is not known how many of the severe service machines were built. The ‘extreme service’ option appears to have been dropped around 1971.

Mention must be made of Caterpillar’s cushion hitch. This was not offered on the early 641s but was available as an optional extra from 1968.

When the upgraded 641B was introduced cushion hitch was still an option and was not made a standard fit item until around 1974.

Due to the hard riding nature of these scrapers, most purchasers opted for the cushion hitch.


In keeping with other surviving members of the 600 family the 641 was upgraded to the 641B series in 1969.

Among the many upgrades were a new eight-speed semi-automatic transmission (which required even less input from the operator than the former model), and an increase in engine horsepower from 500 to 550 at the flywheel.

Although not as popular as the 631 or the larger 651, the 641 was sold in substantial numbers and was successful in Europe, where many were sold and still soldier on.

The model 641 was discontinued in 1978 and has not been replaced in Caterpillar’s scraper range.

Its contemporaries included the Euclid S-32, Allis-Chalmers 460, Wabco 339 and Michigan 410. Of these machines only the Wabco 339 lasted into the 1980s.

The New Zealand connection

Two Caterpillar 641s have been imported into New Zealand.

Brought in by Caterpillar dealer Gough, Gough & Hamer these were second hand units out of Australia and were earlier (41M series) machines. Both had the cushion hitch option fitted.

They went to work for WH Butson in 1977 on the Twizel/Waitaki hydro schemes and later on for Herron Construction of Dunedin.

They have had subsequent owners (and shifted a fair bit of the South Island) since that time. At least one still exists in operational condition.

The Caterpillar 641 is the largest single engined scraper to have operated in New Zealand to date.

For the modeller

At the time of writing no models have ever been issued of the Caterpillar 641 in any scale. This is a pity as even in 1:50th scale a 641 model would be an impressive size.

Brief specifications: Caterpillar 641 (41M series)

Engine: Caterpillar D346 turbocharged V8 diesel rated at 500 fwhp.

Transmission: Caterpillar planetary nine-speed powershift transmission with retarder.

Brakes: Cam operated full air shoe type brakes

Steering: Full hydraulic, 90° to either side

Std.Tyres: 33.5×39 (other options available)

Turning Circle: 44’ 7”

Capacity: 28 cubic yards struck, 38 cubic yards heaped

Operation: All hydraulic

Length: 48’ 4”

Width: 13’ 6”

Height: 13’ 1”

Operating Weight: 47.4 tons (empty) 89 tons (loaded)

Caterpillar's 641 scraper

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