1942 - 1947 Chevrolet Shop Manual



	6-13

	shaft by pressure on any part of the composition. The thrust bearing, on the inside of the camshaft gear, when assembled to the camshaft, determines the amount of camshaft end play. If there is an excessive amount of camshaft end-play, it is necessary to remove the gear and shaft assembly and press the gear farther on the shaft so that the thrust plate is tight, yet free to revolve to a maximum of .003" clearance, Fig. 21. When the camshaft and gear are assembled to the engine, it is important that the punch marks on both the camshaft and the crankshaft gear be lined up, directly opposite each other. The camshaft will then be in its proper position and the valves will open and close in proper relation to the movement of the pistons.	gear for run-out with a dial indicator. This should not exceed .003". Then check the run-out of the camshaft gear. This should not exceed .004". The method of checking run-out is illustrated in Fig. 22. If timing gear run-out is greater than specified above, remove the gear and check for burrs on the shaft or gear that might cause the condition. If unable to overcome the trouble in this manner, replace the gear at fault with a new one. Back-lash between the timing gear teeth should be checked with a feeler gauge as shown in Fig. 23. The back-lash should not be less than .002" nor more than .005". Valve Timing Fig. 24 is the valve timing diagram for all 1942 engines. Note that the intake valve starts to open 3 degrees before upper dead center and remains open for 218 degrees, closing 35 degrees past lower dead center.


	Fig. 22-Checking Run-Out of Timing Gears After the camshaft and crankshaft gears are in their proper places, check the crankshaft timing

		Fig. 24—Valve Timing Diagram The exhaust valve starts to open 46 degrees before lower dead center and remains open for 231 degrees, closing 5 degrees past upper dead center. To check the valve timing, use number 1 cylinder exhaust valve. 1. Tighten the adjusting screw to just remove all tappet clearance. 2. Hand crank the engine until the number 1 cylinder exhaust valve starts to close. Continue cranking the engine until the triangular mark on the flywheel lines up with the pointer in the flywheel housing. 3. Mount a dial gauge on the rocker shaft support with the spindle of the indicator on top of
	Fig. 23—Checklng Timing Gear Back-Lash