Classic Machines Scrapers

Classic Machines: The Caterpillar 623 series scrapers

In 1972, Caterpillar was faced with a problem. To remain competitive it needed to upgrade its existing J621 elevating scraper, which was itself an upgrade of the former model J619.

One of the principal criticisms of the J621 was its rather poor performing elevator which was sluggish compared to its rivals and which did not work particularly well in tightly packed or very free flowing materials.

Caterpillar, which by now owned Johnson (the original manufacturer of the elevating mechanism for Caterpillar’s J619 and J621) undertook an extensive redesign of the bowl and elevator assembly to make it more “user-friendly”.

Again using the tractor unit of the 621 motor scraper, now fitted with cushion hitch, an option not previously available on the J621, the new scraper, named the 623 made its debut in 1972.

Powered with a Caterpillar model D336TA V8 turbocharged and after-cooled diesel rated at 300 flywheel horsepower, this was the identical powertrain fitted to late production J621s.

So, apart from an increased capacity hydraulic pump and tank and the addition of cushion hitch, all the ‘new’ parts lay in the elevating scraper.

Featuring a very slight increase in cubic capacity (from 21½ cubic yards up to 22 cubic yards) the most significant changes lay in the bowl’s construction which went from externally box-braced steel sheet on the J621, to composite box construction on the 623 making for a much more robust and modern looking structure.

Surprisingly though, the 623 scraper still retained the outside supported rear axle of the former J621, a bit of an anachronism really when all its competitors apart from Fiat-Allis had cantilever rear axles.

The other major development was, of course, in the elevator mechanism whose speed had increased considerably and was now far more able to cope with different materials.

However, the 623 was destined to remain in production for only two years and should really be considered an interim model as it was replaced in 1974 by the vastly improved 623B.

Quite possibly the most popular elevating scraper that Caterpillar has manufactured to date, the 623B featured an all-new tractor unit which was also found on the 621B and 627B, a result of a major upgrade by Cat.

Powered by the super reliable model Caterpillar 3406, 6-cylinder inline diesel, the 623B had an extra 30 more horses to pull it around the jobsite and was a quantum leap over the previous 623.

Remaining in continuous production for 13 years, which is a reflection of how good the machine was, the 623B was replaced by the 623E in May of 1986.

The 623B Described

We’ve focused on the 623B as it was in production for longer than the original 623.

Powered by a Caterpillar 3406TA, 6-cylinder, turbocharged and aftercooled diesel rated at 330 flywheel horsepower, the 623B featured a variable capacity torque converter, attached to the semi-automatic 8-speed powershift transmission.

This allowed for more power to the elevator pump when loading and also reduced wheel slippage during the loading cycle.

A foot operated differential lock was also provided to control wheel spin in slippery underfoot conditions. Caterpillar planetary final drives completed the power train.

To stop the 623B, air pressurised, cam-operated shoe brakes were fitted to both tractor and scraper.

These were sequenced to brake the scraper first as an aid to prevent jackknifing.

In addition, a hydraulic retarder was offered as an optional extra.

Usual tyre fitment was the 29.5×29, 28-ply E2 on both tractor and scraper although most operators seemed to opt for the 29.5×29, 34-ply E3 so that they didn’t exceed ton-mph ratings quite so easily.

As mentioned previously, Caterpillar’s cushion hitch was offered as standard equipment to give the operator a better ride.

Steering was the typical Caterpillar arrangement of two double acting hydraulic cylinders mounted up high on the gooseneck and acting through multiplier linkages.

A great improvement over earlier Cat scrapers, the operator’s compartment was mounted on isolation dampers and featured a full hydraulic suspension seat and an ergonomically designed work environment.

Visibility was quite good from the seat but was slightly restricted to the right by the air cleaner assembly.

The muffler and exhaust were placed well aft on the engine thereby reducing the noise and heat for the operator.

A welcome option for colder climates was the availability of a full ROPS cab with sound insulation and air conditioning.

Caterpillar 623B scrapers were all-hydraulically operated and rated at 22 cubic yards heaped.

The elevator featured 15 flights measuring 7’ 5” in length, driven by a two speed reversible hydraulic motor.

During ejection, which was a two stage process, the entire front floor including the cutting edge retracted back on outside hung rollers to about halfway allowing the load to drop out, then the ejector bulldozed the remainder of the load out through the opening, the retracted cutting edge acting as a strike off or leveling plate.

Upon returning to the loading position the sliding floor was held in place by a hydraulic lock.

Four bolt-on teeth could be fitted to the cutting edge to aid in breaking up and loading hard or cohesive soils.

An item not found on the J619 or J621 was the addition of a rock guard to the top of the elevator assembly.

With the increase in elevator power and speed came the distinct possibility that the operator could be ‘crowned’ by a flying rock thrown from the top of the elevator.

On the original 623 this guard was a tubular structure with mesh inserts, but on the 623B it was fully enclosed by steel.

Contemporaries of the 623B included the excellent Wabco 222G, Michigan 210H, Terex S-23E and Fiat-Allis 261.

The NZ Connection

New Zealand Roadmakers got the first two Cat 623Bs imported into the country by Goughs and these later migrated to Cloutman Bros ironsand mining operation in Waiuku, south of Auckland.

Neil Housing of New Lynn also had a pair of 623Bs, quite possibly the ex-Cloutman machines.

For the Model Collector

Sadly no one makes a model of the 623 or 623B in any scale but there is a 1:50th scale model of the much later 623G produced by Norscot.

Unfortunately this is not one of Norscot’s better models and is in fact quite crude considering it is a reasonably recent issue.

It also contains more than its fair share of inaccuracies and needs work to even properly represent a 623G!

However, theoretically, an enterprising modeller could remove the elevator mechanism and cushion hitch from this model and transplant it into NZG’s elderly 621 open bowl scraper (with suitable modifications), thereby creating an early 623 but quite a bit of ‘surgery’ would be involved.

It is fair to say that model collectors are not well catered for when it comes to elevating scrapers.

Brief Specifications – Caterpillar 623B

Engine:                        Caterpillar 3406TA, turbocharged, aftercooled 6-cylinder, inline diesel rated at 330 flywheel horsepower at 1900rpm.

Transmission:             Caterpillar 8-speed semi-automatic planetary powershift transmission with variable input torque converter

Top Speed:                 Approx. 33mph

Brakes:                        Expanding shoe on all wheels, sequenced to brake scraper first

Steering:                      Full hydraulic

Turning Circle:            37’ 4”

Capacity:                    22 cubic yards

Elevator Flights:          15

Elevator Speed:           273 feet per minute (low), 361 feet per minute (high)

Length:                        41’ 1”

Width:                         11’ 8”

Height:                        12’ 2”

Operating Weight:       34½ tons (empty), 59½ tons (loaded)

Caterpillar's 623 scraper

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