(a) =WORN CAM GEARS= change timing because of play, or “back lash” in the teeth, or cause a howling or grinding noise, that will cause the owner to believe that the end of the engine is near. =MISFIRING= and =LOSS= of power are probable results of a change in the timing. If any of the teeth are stripped from the gear you may be sure that the timing is changed. Replacement with a new gear is the only cure for a worn or broken gear. (b) =GEARS NOT IN PROPER MESH= due to an error in assembling the gears, will prevent the engine from being started, or cause misfiring and loss of power. The maker of the engine generally marks the teeth that go together, but if no such marks appear, the owner should center punch or scratch them before taking down the engine. (c) =A GEAR SLIPPING ON THE SHAFT=, due to a missing key in the gear, or to a loose set-screw will cause all of the troubles due to a change in the timing. Examine the key carefully, for dirt often collects in the key-way to such an extent that it is liable to be mistaken for the key. Keys and pins have sheared in two, allowing the shaft to slip in the gear. (d) =WORN CAM-SHAFT BEARINGS= are the cause of trouble, as they will change both the timing and the lift of the valves. If much play exists in the bearing, it will prevent the valves from lifting at the proper time, and will also reduce the lift by the amount of the play, which sometimes has a considerable effect on the free passage of the gases. If the cam-shaft bearings are of the bushing type they should be replaced with new paying attention at the same time to the condition of the shaft. If rough or shouldered the shaft should be machined to a dead smooth surface. If on a large engine and of the adjustable type, the shims should be removed as required or the wedges adjusted. (e) =LOOSE CAMS OR ECCENTRICS= will change the timing because of lost or sheared keys. If your cams are not integral with the shaft, look them over occasionally and be sure that the keys are tight. Loose cams will produce thumping and grinding and may often be located by the sound. See that the key-way is not worn when fitting keys. If the cams are fitted with taper pins it would be well to ream the hole before placing new pins, as there is a liability of the hole being worn oval. (f) =A TWISTED OR SPRUNG CAM-SHAFT= will change the positions of the cams relative to one another, and not only will change the time of all cylinders, but will change their time relatively causing the engine to run out of balance, or produce an unusual vibration. (g) =WORN CAMS= are causes of a change of timing on all types of engines, and are the most frequent cause of reduced valve lift with its consequent trouble of overheating. If the outline or contour of a cam is changed with wear it should be replaced, if keyed to the shaft, as it will be a constant source of trouble. If the cams and cam-shaft are in one integral piece, it will be necessary to replace the entire shaft.