The ignition was by high-tension magneto and spark plug and this decision to change from the make-and-break system was undoubtedly the correct one, just as adoption of the other form originally was logical under the circumstances that existed then. The high-tension system was simpler and had now collected more service experience. The magneto was driven through the camshaft gear, and a shelf, or bracket, cast as an integral part of the case, was provided for mounting it. The spark advance control was in the magneto and, since spark timing was the only means of regulating the engine power and speed, a wide range of adjustment was provided.
The engine had the controllable compression release which had been added to the No. 2 and No. 3 flat engines, although mechanically it was considerably altered from the original design. Instead of the movable stop operating directly on the rocker roller to hold the exhaust valve open, it was located underneath a collar on the pushrod. This stop was hinged to the crankcase and actuated by a small rod running along and supported by the crankcase deck. Longitudinal movement of this rod in one direction would, by spring pressure on each stop, push them underneath the collars as the exhaust valves were successively opened. A reverse movement of the rod would release them (see Figure [10f]). Why they retained the method of manually operating the compression release, which was the same as had been used in the 1904-1905 engine, is not quite clear. That is, the mechanism was put into operation by pulling a wire running from the pilot to a lever actuating the cam which moved the control rod. When normal valve operation was subsequently desired, the pilot was compelled to reach with his hand and operate the lever manually, whereas a second wire or push-pull mechanism would have obviated the necessity for both the awkward manual operation of the lever and the gear guard which was added to protect the pilot's hand, the lever being located close to the camshaft gear.
The 4-cylinder vertical engine was a considerable improvement over the previous designs. They had obtained a power increase of about 40 percent, with a weight decrease of 10 percent, and now had an engine whose design was almost standard form for good internal combustion engines for years to come. In fact, had they split the crankcase at the crankshaft center line and operated the inlet valves mechanically, they would have had what could be termed a truly modern design. They needed more cylinder cooling, both barrel and head, particularly the latter, and an opened-up induction system for maximum power output, but this was not what they were yet striving for. They had directly stated that they were much more interested in reliability than light weight.
This engine model was the only one of the Wright designs to be licensed and produced abroad, being manufactured in Germany by the Neue Automobil-Gesellschaft and by Bariquand et Marré in France. The latter was much more prominent and their engines were used in several early European airplanes.
Figure 11.—4-Cylinder vertical engine assembly, Bariquand et Marré version. (Drawing courtesy Bristol Siddeley Engines, Ltd.)