Caterpillar Service Magazine. Nov. 16, 1953
The D8 pusher was a more powerful track-type tractor that joined the Caterpillar “family”. The machine had been designated as the D8 Pusher Tractor. Its intended use is/was, as the name implies, push loading scrapers. With increased weight and a more powerful engine combined with the low forward and high reverse speed transmission, this machine offers the best in pusher tractors design.
Included as a part of the pusher tractor arrangement was a No.25 Cable Control Unit, an 8S Bulldozer blade with special trunnions and a 1900 pound overweight mounted on the rear of the tractor.
The weight of the complete D8 Pusher Tractor arrangement is 49,940 pounds. This exceeded by approximately 3 tons the weight of a standard D8 Tractor equipped with the No. 25 cable Control Unit and an 8S Bulldozer. The increased overall weight, is the result of a slightly heavier engine and heavier frame than those used on the standard D8 Tractor.
Many of the parts used in the D8 Pusher Tractor are/were identical to those used in a standard D8 Tractor. The track and track components such as roller frame, idlers and sprockets are identical. The main frame engine support frame of the D8 Pusher Tractor is several hundred pounds heavier. Dimensionally, the width and depth of the frame is the same as the standard box section type.
Heavy duty track roller guards, offered as an attachment for the standard D8 Tractor, are included as original equipment on the D8 Pusher Tractor arrangement.
A new two-piece crankcase guard, announced in the Service Magazine of June 20,1953 is assembled to lugs on the inner side of the main frame. This guard provides complete protection for the underside of the engine.
All recent improvements to the standard D8 Tractor, such as the new oil type flywheel clutch, greater capacity steering clutches and new steering clutch controls, are also included in the D8 Pusher Tractor.
The transmission used in the pusher tractor is of the same basic design as that use in D8 Tractors, 2U21513 and up. All of the constant mesh gears on the upper shaft and countershaft have bore bushing pressed into the gears. The complete gear assembly rotates on hardened steel sleeves which are splined to the transmission shafts. Transmission speed ranges available with the D8 Pusher Tractor transmissions are as follows:
1st 2nd 3rd 4th 5th
Forward 1.4 2.3 3.1 3.8 5.0
Reverse 1.9 3.0 5.2
The engine use in the D8 Pusher Tractor is a 6 cylinder 5 3/4” bore 8” stroke Diesel engine. From outward appearances this engine may seem to be the same engine as that used in the standard D8 Tractor. However, many of the internal parts are different as the engine operates at a full load speed of 1200 RPM and develops considerably more brake horsepower.
A damper is used on the crankshaft of the D8 Pusher Tractor engine to reduce torsional vibrations which are encountered at the higher speeds of this engine. Since the vibration damper is mounted on the front end of the crankshaft, all parts in front of the vibration damper have been moved forward about 1 1/2”. A spacer has been added to the fan support to move the fan forward.
The lubricating oil system has a new gear-type, positive displacement lubricating oil pump and maintains a constant pressure with a controlled inlet. The control system is similar to that on the 4”, 4 ½” and 51/8” bore Diesel engines. The oil pump and control valve is mounted inside of and onto the oil pan. Oil pump drive is different from that found on the standard D8 Tractor engine. Drive is accomplished from the crankshaft through an idler gear in the timing gear train. To simplify oil pump removal, the drive gear is connected to the oil pump shaft with a splined coupling. Lines leading to the front and rear scavenge suction bells have been changed.
Pistons, piston rings and piston pins in this new engine are the same as those used in the D397, D386, D375 and D364 Diesel Engines. Pistons have heat plugs in the crater and the piston pins have a heavy wall section. Connecting rods have the same general appearance as those in a standard D8 Tractor engine. There is, however, one important difference: To accommodate the larger piston pins, rods have pin bores which are .070” larger.
Considerable changes have been made to the valve train. Camshaft lobe profile design closely parallels that of the D397 and D375 Diesel Engines. The standard D8 Tractor engine uses an entirely different camshaft. Valves are equipped with rotators and shorter and heavier valve springs. Both the inlet and exhaust valves seat against hardened steel inserts in the cylinder heads.
The fuel system and governor of this engine is basically the same as that of the standard D8 Tractor. Fuel pump rack settings and adjusted governor speeds are different. Engine full load speed is 1200 RPM and the high idle speed is 1320 RPM. Fuel rack settings with the 3H1690 Gauge are 0.475”, with the 1f 7945 Fixture the rack setting is 1.675”. Because of the higher engine speed, governor flywheels are lighter. The capacity of the air induction system has been increased by using a larger inlet manifold, larger air transfer pipe and a larger (13” diameter) air cleaner.
Crankcase lubricating oil recommendations for the D8 Pusher Tractor engine are different form those recommendations for the standard D8 Tractor engine. Because of the higher speed of this engine, at the time, it is recommended that Superior Lubricants (Series 2) be used with oil change periods and filter element change periods at 240 hour intervals when the sulphur content of the fuel does not exceed 0.4% to 1.0%, reduce oil change and filter change periods reduce oil change and filter change to every 120 hours.
When the sulphur content of the fuel is 1.5% or higher, oil change intervals should be reduced to 60 hours. The oil filters which are of the full-flow type must be changed at every oil change. Other lubrication recommendations are the same as those for the standard D8 Tractor machine serial numbers 2U21513 and up.
Offered as a special attachment for the D8 Pusher Tractor is a 3H4171 tandem Pusher Frame Group. This group consists of an additional pair of
trunnions which are weld to the special trunnion plates used with the 8
S Bulldozer blade and a “C” frame which is supported at the rear of the tractor by the drawbar. A dome-shaped block, resembling the pusher block on a scraper, is a part of the “C” frame and is the pusher block for the second pusher tractor.