Practical Hand Book of Gas, Oil and Steam Engines / Stationary, Marine, Traction; Gas Burners, Oil Burners, Etc.; Farm, Traction, Automobile, Locomotive; A simple, practical and comprehensive book on the construction, operation and repair of all kinds of engines. Dealing with the various parts in detail and the various types of engines and also the use of different kinds of fuel.

by John B. Rathbun

In timing an engine great care should be taken to get the crank exactly on the dead center.

(139) Timing Offset Cylinders.

The only difference in timing engines with offset cylinders and timing those with the center line of the cylinder in direct line with the crank shaft, is in the locating of the dead center. With no offset, the center of the cylinder, the crank pin and the crank shaft are all in one direct line when the engine is on the dead center.

With offset cylinders the crank pin lies to one side of the cylinder center line when on the dead center, on either the inner, or the outer center. To find the center on an offset engine proceed as follows:

Turn the engine over slowly until the crank-pin reaches either the extreme top or bottom point of the crank circle, depending on which center is to be determined, and then turn very slowly until the centers of the piston-pin, crank-pin, and crank-shaft are in line. With the average engine this will be found a difficult and tedious job, and it will be well to mark the dead center on the flywheel or other convenient point to prevent a repetition of the job. The quickest method of accomplishing the feat is to remove the spark plug or relief cock to gain access to the piston, and insert a rod or pointer in the opening thus provided.

Draw the piston back a short distance from the end of the stroke with the pointer resting on the head of the piston, and mark this position of the piston both on the pointer, and on the flywheel, using some stationary part of the engine as a reference point.

Now turn the crank over the center line until the piston is moving in the opposite direction, and is the same distance from the end of the stroke as shown by the mark on the pointer. Mark this position on the flywheel using the same reference mark as before. We now have two marks on the flywheel, and will bisect the distance between them, using the dividing mark to obtain the center.

Place the bisection mark even with the reference point used for obtaining the two previous marks on the flywheel, and the engine will be on the true dead center, as the flywheel is now midway between two points of equal stroke.

(140) Auxiliary Exhaust Ports.

To decrease the amount of hot gas and flame passing over the exhaust valve some makers provide their engines with auxiliary exhaust ports, which are similar to the exhaust ports used on two stroke cycle engines.