The model 627 twin powered motor scraper marked a paradigm shift for Caterpillar in terms of design and sent a clear message to Terex that Caterpillar was about to take it on, and at its own game. By Richard Campbell.
Prior to the release of the first Caterpillar 627 motor scrapers in 1968, there were only two other twin powered motor scrapers in Caterpillar’s motor scraper range – the model 657 and the 3-axle model 666, both big, high yardage machines, both of which were introduced in 1962.
The model 627 was specifically designed to fill a gap in Caterpillar’s product range and take on the Terex TS-14 that, at the time, was the only 14 cubic yard twin powered scraper available in the marketplace. Terex had completely dominated the twin powered motor scraper market since the early 1950s, and when the TS-14 was introduced in 1960 it created a whole new market segment for this type of machine.
Caterpillar took an uncharacteristically long time to bring a competitive machine to the marketplace to take on the TS-14, with over eight years elapsing before the first 627 appeared. However, the long gestation period did allow Caterpillar to address some of the faults that were inherent in the TS-14 such as marginal horsepower and the lack of a power-down bowl or apron. Caterpillar also equipped the 627 with a bulldozer ejector to ensure that sticky material didn’t ball up inside the bowl floor as the TS-14 was prone to do in certain plastic-type clays.
The Caterpillar 627 tractor unit was based upon the already-in-production model 621 single engined motor scraper, but instead of using that machine’s D336T engine, the 627 was powered by two Caterpillar D333T 6-cylinder turbocharged diesel engines, one in the tractor, the other in the scraper, and each rated at 225 flywheel horsepower. These were connected to separate Caterpillar 8-speed manually selected powershift transmissions. In a rather clever twist, the rear engine and transmission could be removed as a module to reduce dismantling time should major repairs be necessary.
The 627s scraper held 14 cubic yards struck and 20 cubic yards heaped, and all control functions were hydraulic. Two double-acting hydraulic cylinders provided bowl downforce, something that the competing Terex TS-14 lacked, relying on gravity alone to lower the bowl. Another double-acting cylinder mounted in the gooseneck provided the power to open and close the apron via a multiplier linkage and rod. A single double-acting cylinder took care of the bulldozer ejector assembly which ran on hardened steel rollers to reduce friction. Steering was accomplished by two double-acting hydraulic cylinders mounted high on the gooseneck and acting through multiplier linkage to achieve a 90 degree turn in either direction.
The Caterpillar 627 was launched with the usual Caterpillar style and flair midway through 1968 and immediately made a name for itself, becoming very popular.
Terex, the major competitor, had a small ace up its sleeve in the form of “Terex Twin-Hitch”, a device that could be field or factory installed to existing TS-14s allowing two similarly equipped units to load each other in the absence of a bulldozer. This idea, while now very commonplace, was quite innovative at the time and Caterpillar had to find a way of countering it. Caterpillar engineers came up with the “Push-Pull” system that basically mirrored the Terex Twin-Hitch, but was hydraulically rather than air operated. The only problem was that Caterpillar’s push-pull could not be field fitted to existing units and had to be installed at the factory when the machine was manufactured. Some main frame strengthening was required due to the amount of stress push-pull loading placed on the hitch and this could only be done at base level on the production line.
But, Caterpillar had another innovation to add to the 627 in the form of cushion hitch that became standard on the 771st unit to leave the factory. Cushion hitch was a clever piece of engineering utilising a parallel link arrangement with a nitrogen/oil shock absorbing cylinder that prevented the repetitive bouncing effect (or loping as it was called), common to 2-axle overhung scrapers, giving the operator an improved ride and reducing shock transmitted through the tractor frame. Cushion hitch was a big selling plus for Caterpillar over the Terex TS-14 that had no form of suspension whatsoever, even in its later versions.
A slightly improved version of the 627, the 68M series was introduced in late 1969, incorporating all the new Caterpillar goodies and addressing faults that had shown up on machines that were in service. Along with cushion hitch and factory installed push-pull, the 68M series 627 also had Caterpillar’s new 8-speed semi-automatic powershift transmission that was a much more flexible transmission than the manually selected 8-speed type offered on the earlier 54K series machines.
Time-line evolution of the Caterpillar 627
The Caterpillar 627 has had several models since it first appeared in 1968 and the type is still in production today, albeit in considerably altered form and slightly increased capacity.
Early production versions were always called 627s, never “627A” as some publications erroneously state. In 1972 the 627B was introduced featuring a new engine, the Caterpillar 3306T. That model was superseded in 1986 by the 627E which remained in production until 1993 when it was replaced by the 627F. A new millennium also found a new 627, the model 627G that remained in production until the short-lived 627H came along around 2010. The current production model 627K appeared in 2012. Caterpillar is currently the only manufacturer of twin-powered motor scrapers left in the world, with all their competitors having been taken over or gone out of business, so variants of the 627 are likely to be around well into the future. All variants of the Caterpillar 627 released to date have seen service in New Zealand, the type proving very popular here.
For the model collector
Surprisingly, given the popularity of the type, there have been very few models of the Caterpillar 627 issued, and in fact there are only three of them, two to 1:50 scale and one to 1:87. The first model to appear was made by NZG Models of Germany, and was first issued way back in 1969. NZG’s model represents the first production 54K series without cushion hitch, and, as per usual NZG practice, the model has been reissued multiple times over the years in various guises, and also with and without the Caterpillars push-pull hitch.
Although basically accurate, the NZG model is really showing its age detail-wise and some time and effort must be spent to turn it into a really good likeness of the real thing. The next offering is by Diecast Masters who offer a very smart looking 627K (the current production version at time of writing). This is a good little model with adequate detail and will sit well amongst any collection of 1:50 motor scrapers.
Lastly is the 1:87 scale 627G offered by Norscot. This model is a little crude compared to the two 1:50 offerings mentioned above and has massively over-scale handrails, but if 1:87 is your choice of scale, it is the only game in town.
Brief Specifications – Cat 627 (68M series)
Engines (front): Caterpillar D333T, 6-cylinder, turbocharged, inline diesel engine rated at 225 flywheel horsepower at 2,200 rpm.
Engines (rear): Caterpillar D333T, 6-cylinder, turbocharged, inline diesel engine rated at 225 flywheel horsepower at 2,200 rpm.
Transmission (f): Caterpillar 8-speed semi-automatic powershift.
Transmission (r): Caterpillar 4-speed powershift, full torque converter drive.
Top Speed: 36 mph.
Brakes: Full air, S-cam operated expanding shoe brakes.
Steering: Full hydraulic using two double acting cylinders with multiplier linkage.
Turn Circle: 33’ 10”.
Tyres (std): 29.5-29, 28-ply E3 (other options available).
Capacity: 14 cubic yards struck, 20 cubic yards heaped.
Operation: All hydraulic.
Length: 49’ 5” (with Cat push-pull installed)
Width: 11’ 7”.
Height: 11’ 2”.
Operating Weight: 34.9 tons empty, 53.1 tons loaded (with cushion hitch and push-pull).