I guess I would call this a second generation D7. The D7 of the late '40's and early 50's was a '3TD7'. The 3T refers to the first two digits in the serial number. The model shown here is a 17A which was made subsequent to that, which is a D7 series with matched the 13A and 14A D8s. They were larger and more powerful than the previous model, but they still featured cable blades and a 4 cylinder engine with a side saddle pony engine which started either with an electric start or a crank down through the engine housing.
Leslie Newman of Bumpass Virginia, USA who graciously contributed these photos, had just completed some repairs on this machine which he is restoring, and the photos are in celebration of his getting it running for the first time. The Canopy and the Hood had not yet been installed. Also obviously the angle dozer was not installed yet either. What you are looking at is what is rather unimaginatively called the C-frame. The Blade pivots on the center pin in the middle, and can be angled left or right by disconnecting the side braces, and then by manually moving the blade to the new position. There was a lot of innovation between this blade and the PAT blades you see on small dozers now. PAT stands for 'Power/Angle/Tilt'. Perhaps this blade should have been called 'MAT' for "Manual/Angle/Tilt".
|No 25 Cable Control|
Also shown here clearly is the cable control unit. It was driven off PTO on the back of the dozer so you could not lift the blade with the clutch released. The tube up the right side carries the cable forward. A single lever control engages a friction to lift the blade, sets the brake to hold the blade, and drops the blade. Perhaps more accurately, I should say releases the brake. The brake is actually set while you are lifting the blade as it is a band brake, and the lifting simple winds through the friction. You see, one of the neat things about an external band brake is that it is essentially a one way brake. With the external band anchored on one end, rotation in one direction will pull the band ever tighter, and rotation the other way will loosen it.
This rear mounted unit also was used for other purposes. As you can see from the photo the cable for the blade goes through a couple blocks and forward up the right side. The alternative use for the rear cable control is for towed equipment. the two rectangular holes in the lower drum are cable holes to pass two lines (there are 2 drums inside). If the machine was being used to pull an old style cable controlled scraper (or can as they are called), the two lines are used to control the scraper (and you either take the blade off or tie it up). The alternative approach to blade control was a front mounted drive (off the front of the crankshaft). In this configuration the drum and clutches were mounted in front of the radiator and used exclusively for lifting the blade, leaving the rear of the machine free for either a double drum control unit such as this (so you could pull the scraper AND use the blade) or could mount a towing winch on the back. These control cable winches are not suitable for dragging logs for example
Anyone who has a dozer with a cable control knows what 'two blocking' means. For the rest of you just imagine what happens when you lift the blade until the block (pulley) on the C-Frame hits the block (pulley) on the radiator. That is a 4 part line meaning that the leverage which it has is compounded. In case you still don't understand, 'two blocking' occurs when the two blocks hit one another, which often results in the cable breaking and then the blade which had been going up goes down rapidly. These days most hoists and the like which have the capability of 'two blocking' have some sort of a safety shutdown which is suppose to prevent "two blocking" as the result can be a safety hazard
The photo at the right shows the pony motor or the goat motor as it is sometimes called. We have usually called it the 'goat' but 'pony' is apparently more common, but I am not sure of this. Anyhow if you look carefully you will see a 2 cylinder flathead engine with an updraft carburetor. It can be started one of two ways. The vertical shaft extending through the hood is for hand cranking. You stick a crank on the top of the shaft and crank while standing on the track. On older machines this was the only option. On this machine, however, you can see an electric starter (the black thing) on the back of the motor. The red Battery cable went off to a better somewhere allowing the wonders of electric starting. This machine was not new enough, however, to have the luxury of 'in seat starting'. Even though you could start the goat motor with a push button, you still had to climb out on the track to start the main engine. The two levers to the rear of the motor are the main engine pinion and clutch controls. Out of site is a 3rd lever which is a high-low shifter which gives you a choice of speeds to spin the main engine. There is also a compression release lever. Releasing the compression makes it easier to spin up the main motor, and the two speed gives you a choice of spin speeds.
As complex as this process is, it was really well liked by most owners. The starting motor coupled with a very slow maximum RPM for the engine (under 1000 RPM) made these machines last one very long time. An engine like this needs to be warmed up some anyway, and the horsing around to get it started guaranteed that the operator would allow at least some warm up time. In cold weather the engine often needed to be cranked for 5 to 10 minutes before it would start. During this time the oil pressure would come up, and heat from the goat motor (which was cooled with engine water would begin to warm. Even the heat from the exhaust of the goat motor was captured to warm the intake manifold for the main engine, so not only would the cold iron begin to warm via circulating water, the air entering the engine would be prewarmed. These are all critical items for an engine dependent on compression ignition. The high performance diesels of today start a lot better in cold weather, but they require some help as well. They often need a whif of ether or need glow plugs to get going.