Koban

KOBAN - The Perfect Rowboat Motor

By Christopher Scratch, Special Features Contributor, AOMCI


During the formative years of outboard motor production, the typical detachable rowboat motor design consisted of a single cylinder engine, with the cylinder pointing in various directions, depending on the year and manufacturer. The early Waterman Porto motors utilized a vertical cylinder arrangement from 1906 to 1911; in 1912, the Waterman flopped the cylinder onto its back and had it pointing out towards the rear. This lasted for one year, then in 1913, Waterman joined other motor manufacturers (notably Evinrude) in switching to a forward-pointing cylinder design, which had basically become the industry standard. Several other motor builders also marketed detachable rowboat motors in 1913, and they too had the cylinder pointing forward into the boat, with the spark plug always in close proximity to the operators elbow. However, in 1914 the growing marketplace welcomed a few motors offering a completely different appearance, inasmuch as they were two-cylinder engines, which, while built for various in-board configurations as in-line twins, and in Europe as opposed twin-cylinder motors, had not previously been available in North America as an outboard. Among these new players in the detachable rowboat motor game was the “Koban".

The name Koban itself was derived from the combination of the surnames of its inventors, Arthur Koch and Walter Bannon. These gentlemen were residents of Milwaukee, WI, and reportedly finished designing their twin-cylinder opposed motor in late 1913, which was just in time to build product for the 1914 model year. This motor utilized battery powered spark-coil & timer ignition and a gravity-fed “air-float” check-valve carburetor. Steering was accomplished through the use of a rudder controlled by a suitable linkage to the tiller handle. The detachable cylinder heads featured cooling fins sprouting from the outer surface. The very distinctive spoked flywheel lacked a starting knob; rather, the operator could simply grip the rim of the wheel and give it a spin in order to start the engine. Safety inspectors of modern times would have no doubt voiced some concerns with the spinning spokes of the flywheel having some capability to act as lawn-mower blades, but of course in that era, safety was not necessarily the rule of the day. Nonetheless, the 1914 models proved popular enough to customers looking for additional horse-power that “would not shake the boat” that the Kobans were marketed again in 1915 with some improvements, most notably the implementation of a flywheel magneto. The fins on the cylinder heads were not present on the 1915 motors, as the head design was revised to a smooth outer shell instead of the raised fins.

The Koban enjoyed some sales success, as they were touted as being able to provide vibration free operation, and boasted twice the cylinder capacity of any other rowboat motor available at that time. In keeping with the somewhat creative advertising that is so much a part of our culture, a large number of claims were made that the Koban supposedly could live up to. In fact, the title of this article is taken directly from Koban literature and advertisements of the day. Contained within those ads and flyers are vigorous assertions of the following desirable qualities;



1915 Koban Model C - The specifications of the 1915 motors listed the bore at 2.625” with a stroke of 2.375”, producing 3 horsepower @ 900 RPM. With an advertised weight in the 65 to 70 pound vicinity, the Koban represented a somewhat heftier alternative for hanging on a boat transom. Twin-cylinder configuration and removable cylinder heads aside, the Koban motor assembly was unique inasmuch as the cylinders themselves were cast integral with the crankcase housing, which was known as casting en bloc (a French term for “as a whole”). When one ponders the reasoning behind such a design, certainly rigidity of the block assembly would come to the forefront. One other potential reward for use of the en bloc configuration would be that such a structure allows both cylinders to be line-bored in one set-up during the machining phase, thereby insuring that both bores were accurately aligned and concentric to each other, giving machining repeatability and best economy from a manufacturing standpoint. Although one would think that utilization of this design might make life easier when it came time to put the motor together, actually the reverse was true; the pistons could not be inserted through the obvious port of entry, which would be the cylinder head end; rather, the pistons had to be installed through the center of the motor & entered the bottom of the cylinder first. This was partially because of the fact that the cylinders are directly opposite of each other, and are not staggered or Twin-cylinder configuration and removable cylinder heads aside, the Koban motor assembly was unique inasmuch as the cylinders themselves were cast integral with the crankcase housing, which was known as casting en bloc (a French term for “as a whole”). When one ponders the reasoning behind such a design, certainly rigidity of the block assembly would come to the forefront. One other potential reward for use of the en bloc configuration would be that such a structure allows both cylinders to be line-bored in one set-up during the machining phase, thereby insuring that both bores were accurately aligned and concentric to each other, giving machining repeatability and best economy from a manufacturing standpoint. Although one would think that utilization of this design might make life easier when it came time to put the motor together, actually the reverse was true; the pistons could not be inserted through the obvious port of entry, which would be the cylinder head end; rather, the pistons had to be installed through the center of the motor & entered the bottom of the cylinder first. This was partially because of the fact that the cylinders are directly opposite of each other, and are not staggered or offset, making necessary the use of off-set connecting rods which interfere with travel through the cylinder bore if one should try to install or with-draw the pistons through the combustion chamber end of the bore. Thus, the pistons and rods have to be installed head-first into the crankcase end of the bore, utilizing a large chamfer that was cast interiorly of the cylinder block to allow easier piston ring compression during assembly; after which the crankshaft could be fitted in and the connecting rods bolted to it. Even with a fairly spacious inner crankcase chamber, there is precious little room for man-sized hands to maneuver around the reciprocating assembly. Assembling Koban powerheads has the potential for being tedious work. The author has managed to re-assemble two Kobans of the en bloc configuration, and the second time around was no easier or less time-consuming than the first. However, it can be said that considerably fewer utterances of profanities occurred during the reconstruction of the second motor.

With respect to the detachable heads, according to the manufacturers literature, one reason for making the cylinder heads removable was to facilitate easier removal of carbon or other combustion chamber deposits without having to completely disassemble major engine components. Also contained in the information booklet are statements that the aluminum cylinder heads were used because of their stability and resistance to shrinkage regardless of exposure to multiple episodes of heating and cooling, in spite of the fact that the cylinder heads themselves possessed no water passages of any kind; it was felt that the heat dissipation qualities of the aluminum alloy of the day would be sufficient for keeping the heads from being damaged or warped under the hottest operating conditions that the engine might have to endure.

The rest of the powerhead components were fairly basic. The gas tank was made of galvanized 24 gauge pressed steel, with a capacity of just over one gallon, and featured a built-in strainer that was easily removed to allow gas tank cleaning. The flywheel could be either of nickel plated cast iron in the case of battery ignition equipped motors, or polished aluminum for those models utilizing a flywheel magneto. According to some observers, the flywheel magnetos used components not terribly unlike those found in later vintage motors using Quick-Action magnetos.

Koban motors used brass carburetors of two configurations; the early motors used a check-valve “air-float” carburetor, while later models utilized a poppet valve “non-sensitive economy carburetor” with a removable poppet-chamber cap that proudly displayed the “KOBAN” name. Both the upper and lower crankcase covers were of cast aluminum; the upper crankcase cover housed a generous bearing that supported the crankshaft, while the lower cover had an extension cast onto it that held the lower crankshaft bearing as well as served as the means by which to attach the powerhead to the transom bracket. On each side of this center support is a raised circular serrated region which fits into a corresponding serration found to be cast into the transom bracket; these serrations or ridges are what provided the means to stabilize and lock the motor tilt angle. Loosening the retaining bolts on either side of the transom bracket allowed the operator to adjust the angle of the motor to fit the transom of the boat, or to allow the entire motor to be tilted for beaching the craft. A brass tube, which shelters the drive shaft and coupler, telescopes into the aluminum lower crankcase casting. This tube can be raised or lowered by loosening a clamping bolt located at the lower-most section of the aluminum mid-section, thus lengthening or shortening the motor leg to suit transom heights and/or water depths. At the lower end of the brass tube, a bronze support bearing is inserted to provide a bearing surface for the lower end of the driveshaft. On the outside of this brass tube, a brass casting is clamped in place, which forms the forward section of the lower unit housing. The lower front face of the gearcase housing is removable, providing a means of installing and accessing the inner workings of the lower unit, including the prop-shaft and beveled drive gears. The rear wall of the gear housing is spot-faced to provide a thrust-bearing surface for the prop-shaft. Immediately behind the gear housing, a water pump arrangement is installed; the pump is comprised of two gears, which are contained within a recessed cavity, and as these gears mesh, they compress and push water into a chamber inhabited by a ball check valve. Two check valve chambers, one on either side of the pump assembly, give the pump the capability of being able to supply water up to the powerhead regardless of whether the engine is running forwards or backwards. One gear is pinned to the prop-shaft and provides the method by which the pump is driven; the other is mounted on a stud directly below the centerline of the prop-shaft and acts as an idler gear. A brass thrust plate then is bolted over the gears to keep them in place. The gears draw the water in through slots in the sides of the gear recess, and then force the water into the check valve chamber. Brass check valve balls control water movement and keep it flowing upwards to the powerhead while preventing it from escaping back down the system. Water travels through a telescoping brass tube and up to a “T” fitting constructed of suitably-sized brass pipes, which distribute the cooling water out to each cylinder water jacket, thence through the water jacket passages and back out to the lake or river through simple brass pipe dump-offs which vent off the top-side of the cylinder castings. Behind the water pump is where the two-blade bronze propeller of ten-inch diameter is mounted on the prop-shaft; the propeller is locked onto the shaft by means of a press-fit pin.

The powerhead on Koban motors does not pivot, nor does the lower unit. So, steering is accomplished through a suitable tiller linkage, which swings a large brass rudder. The rudder is affixed to the lower unit housing by a simple pivot pin machined on the rudder support strut (which also serves as the skeg, offering minimal protection to the propeller), with the pin fitting into a cavity found on the underside of the gear housing, and is fixed in place by clamping the upper rudder support strut to a square brass bar which is attached to the upper tiller bar linkage. The linkage and rudder arrangement is touted as giving ample turning capability in either direction, and as the ads suggest, one would theoretically still be able to steer the boat even after the motor has come to a halt.


Images of a 1915 Koban

Provided by seller circa 2003 - whereabouts unknown.

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      1915koban-1.jpg   36.85 KB   1/09/2009 9:49 pm
      1915koban-2.jpg   39.19 KB   1/09/2009 9:49 pm
      1915koban-3.jpg   37.15 KB   1/09/2009 9:49 pm
      1915koban-4.jpg   36.89 KB   1/09/2009 9:50 pm
      Koban March 1916 ad.jpg   855.88 KB   1/10/2009 3:47 pm

CategoryKoban
CategoryRowboatMotors

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