Creating quite a stir when it was first announced, the Caterpillar 657 has been the backbone of large capacity scraper fleets since 1962 and remains the largest two axle scraper that Caterpillar have offered to date. By Richard Campbell
The year 1962 was a big one for Caterpillar as it was the year it introduced no less that nine new models of motor scraper into the earthmoving marketplace. Amongst these was the model 657, a machine designed to take on Euclid in the big scraper stakes, and also ultimately dominate the large scraper market.
The roots of the Cat 657 go way back to the late 1950s when every scraper manufacturer was striving to come out with the largest and most powerful motor scraper they could possibly build.
This fervor was spurred on by the Interstate Highway Act which was designed to establish high speed, free flowing motorways from coast to coast across the USA.
Some of the more notable large machines to appear during this highly productive time were the 48 cubic yard MRS I-250, 32 cubic yard LeTourneau-Westinghouse B-70 Tournapull, 28 cubic yard Euclid S-28, 43 cubic yard Michigan 410 and the 40 cubic yard Allis-Chalmers 562. However, while boasting reasonable struck yardage capacities, only the MRS and Allis-Chalmers machines were twin powered.
Caterpillar’s 657 featured a 44 cubic yard (heaped) capacity bowl and a hill-eating 785 horsepower from its two engines. Euclid countered this threat in 1964 with its 818 horsepower, 32 cubic yard capacity model TS-32. So, Caterpillar raised the horsepower of the 657 to 900 flywheel horsepower (combined) and the two rivals fought it out on large jobs across the USA.
However, in this race to be the biggest and best, both of the Euclid and Caterpillar machines had major flaws. The Euclid TS-32 suffered from structural failures of the gooseneck and draft arms its entire production life, often sidelining a complete earthmoving spread at a time until the welders could patch them up again.
The Caterpillar 657, while also suffering some structural problems, was a very hard riding machine, often bouncing (or loping as it was known), so badly that the operator could not utilise the higher gears in the transmission, slowing down production. This repetitive bouncing further contributed to the machine’s structural problems and also damaged many an operator!
The initial model of the Cat 657 was the 31G series, powered by a 450 flywheel horsepower Caterpillar D346T engine in the tractor and a 335 flywheel horsepower Caterpillar D343T engine in the scraper with a 9-speed powershift transmission. As was usual for Caterpillar machines of the period, the purchaser had the option of gasoline engine starting or direct electric starting of the diesel engines. Unusually, Caterpillar did not distinguish between the two starting methods by a change in serial number prefix as had been the case with their earlier DW series motor scrapers. Empty weight of a 31G series 657 was approximately 62 tons.
Early pre-1968 machines are easy to recognise by their rounded fenders on the tractor unit and the lack of a cushion hitch.
In 1968 another major alteration was introduced this time to the bowl lift cylinders which were relocated from the center of the gooseneck to outboard on the bowl’s draft tube. The idea behind this was to lessen the concentrated stresses in the central gooseneck area and to provide more even down pressure across the cutting edge, a feature which was applied to all subsequent Cat scrapers and is still present today.
The cushion hitch
Due to its bad riding characteristics at speed plus reports of a number of catastrophic hitch failures, Caterpillar set about designing a fix for the problem. Unfortunately for Caterpillar, the bad riding problem was not confined to the 657 as most of the two axle Caterpillar scrapers had also been cited for their bad handling and the inability of operators to achieve the full potential of the machines.
Caterpillar’s fix came in the form of a parallelogram linkage connecting tractor and scraper at the hitch in conjunction with a hydraulic cylinder and nitrogen/oil filled shock absorbing accumulator which Caterpillar dubbed the cushion hitch. This reduced the amount of stress in the gooseneck area and while not stopping the first ‘bump’, it did prevent the repetitive bouncing or loping which had been the prime concern of users, giving the operator a far improved ride and reducing the shock loads on the scraper
As is often the case, while fixing one problem this sometimes creates another. In the case of the cushion hitch, it added almost two and a half tons to the machines empty weight, all up high, in the hitch area. Cushion hitch was optional on 657’s built from 1967 onwards but could not be retrofitted to existing machines already in service.
By the time the 657B (68K series) was introduced in 1969, Caterpillar had pretty much ironed out most of the bugs in the machine. From machine s/n 68K749 onwards, the cushion hitch was standard equipment and undoubtedly contributed to the long service life that many of these machines have achieved. Horsepower was now 550 flywheel horsepower in the tractor and 400 flywheel horsepower in the scraper giving the 70-ton machine quite a reasonable power to weight ratio.
The 657B also featured Caterpillars new 8-speed semi-automatic transmission which was being fitted to all new Caterpillar scrapers from the 621B and above. Caterpillar also ‘squared off a lot of the panelwork on the 657B, particularly the front fenders. .
Based on an idea originally conceived by ‘Buster’ Peterson (of the Californian Cat dealer, Peterson Tractor), push-pull allows two 657s to load each other, thereby doing away with the need for a dedicated push tractor in the cut. Once loaded, the machines can operate entirely independently of one another. Caterpillar began offering this option around 1970. The push-pull option is factory fitted and not available as a retrofit for machines already in the field as the tractor frame and hitch are specially reinforced on the production line. As a measure of the push-pull systems popularity, the majority of the 657Bs that Caterpillar manufactured during the machines 15 years production span were delivered with this option.
There are also two later versions of the Caterpillar 657, the 657E and 657G but both of these are more contemporary machines and therefore fall outside the scope of this historical article.
The NZ connection
No Caterpillar 657s have yet made it to New Zealand shores. It is unclear why this is so as there are examples of the larger, single engined models (641 & 651) already in service here. Perhaps they were just too expensive to justify at the time, although your author thinks they could have made a good dent in the hydro projects going on in the South Island at the time.
For the model collector
Joy! Black Rat Models offer an early version of the 31G series 657 while CCM Models make an exceptionally good model of the 657B (with a working cushion hitch no less).
Sadness! Both of these models are really expensive and hard to find. Either one will cost you close to NZ$1,000 and probably more for the Black Rat model.
For those wanting something more contemporary, there is also a 1:50 model of the Cat 657G available. However, while an impressive looking model, it’s accuracy leaves a great deal to be desired and it is a bit light on detail. The model has a few working features and others that should work (like the ejector) but don’t. Purchase if you must but you have been warned!
Brief Specifications – Caterpillar 657B
Engine front: Caterpillar D346T, turbocharged V-8 diesel engine rated at 550 flywheel horsepower at 2000 rpm
Engine rear: Caterpillar D343T, turbocharged 6-cylinder diesel engine rated at 400 flywheel horsepower at 2100 rpm
Transmission: Caterpillar 8-speed semi-automatic powershift transmission
Top Speed: 33 mph
Tyres: Standard, 37.5×39 44-ply, E3
Brakes: Full air, cam operated shoe brakes with hydraulic retarder in transmission
Steering: Twin hydraulic cylinders with multiplier linkage, 90 degrees left & right
Turn Circle: 45’ 1”, and 55’1” to the left if fitted with a ROPS cab
Capacity: 32 cubic yards struck, 44 cubic yards heaped
Operation: All hydraulic
Length: 51’ 8”
Width: 14’ 2”