| September/October 1966

Ottawa Engine

OTTAWA C29067HP 2\1 [2 500 RPM]

It is used in conjunction with the hammer break igniter discussed in the last issue of GEM. The armature of this magneto does not rotate a full circle but turned in short radius by a pushrod, usually the exhaust valve rod, which acts against a cocking lever attached to one end of the armature. This lever, when released, also acts as the hammer to break the points. The base contains two E-shaped field poles cast integral with the base. The field poles and armature are made of laminated soft iron while the base and end plates are of non-magnetic alloy. The field coils are wound on the center bar of each E field pole, consist of several hundred turns of copper wire and are wrapped with insulation cloth. One coil end wire is grounded to the base with its other end connecting to the other coil and that coil's free end passes up through the base to the terminal block. Another wire then runs from the terminal block to the insulated igniter point on the engine. The magnets slip down on the base and are held by a lock screw in each side plate.

In operation, the armature, which is the inductor type with no winding, is rotated until its two wider arms are horizontal or in a straight line with the center poles of the field. This movement also turns the spring lever on the opposite end of the armature from the cocking lever so that it stretches the springs between it and the side plates. At this time the magnetic flow follows the least resistance from the field centers and through the horizontal armature bars. The cocking lever then trips, the springs jerk the spring lever straight and rotate the armature so that its X-shaped bars line up with the top and bottom of the E's of the field poles. The magnetic flow thus shifts from the center of the E's to the top and bottom, passing through the field coils in the process and inducing an electric current in the coil, which flows to the breaker points of the igniter.

Troubleshooting: All electrical connections should be clean and bright. The wire from the terminal block to the engine should have good insulation and preferably pass through a rubber grommet where it leaves the magneto. The armature should rotate freely. If it rubs the field poles it will slow the rotation. The faster the rotation the stronger the current. If it rubs, new bearings must be made-a job for your friendly machinist. The springs must be strong and evenly matched so they do not wear the bearings unevenly. The hooks on the spring ends should be in the center of the springs, not on the edges, also for even pull.

Fiber washers on each end of the armature between the end plates, center the armature and keep it from rubbing the end plates. The field coils are rugged and probably won't need any attention. Clean them with compressed air. If they should be badly oil soaked, clean them as well as possible. Then give them a very quick bath in naptha and dry as quickly as possible. A few coats of shellac will help.

This is a threshing rig busy on the Frank Chaptman farm at Troy Center, Wisconsin.

I threshed 11 days this year with this outfit which consists of a 32 x 54 Avery Thresher and Model L. Case Tractor. In 11 days I threshed a little over 25000 bushels of oats and 750 bushels of wheat. Grain was very good here this year.