1942 - 1947 Chevrolet Shop Manual



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	frame it is not possible to remove the reactionary lever assembly from the transmission operating shaft while the assembly is in the car. To remove the Cabriolet engine, follow instructions given above in Paragraphs 1 through 10, then: Disconnect the vacuum cylinder piston rod and valve link from the reactionary lever system. NOTE—Replace the clevis pin through the piston rod yoke and valve link to prevent upsetting the vacuum valve adjustment. Then proceed as instructed in paragraphs 13 through 17. REPAIR OPERATIONS PISTONS Chevrolet pistons are cast iron surface treated, with a slipper skirt. Three ring grooves are located above the piston pin. The pistons are of unusual design, being cam ground out of round. This out-of-round design compensates for heat expansion along the line of the piston pin bosses. The truck engines use a heavier and more rigid piston than the passenger car engines. The truck piston may be identified by a small forged boss on the lower center of each piston pin boss. Since the truck piston is heavier than the passenger piston, passenger or truck pistons must be used in sets, and the two different types must not be used in the same engine. The lower piston ring on the piston is an oil control ring with ports to allow excess oil, scraped from the sides of the cylinder walls, to be returned to the inside of the pistons and then to the Crankcase, by means of holes drilled in the ring grooves of the piston. Chevrolet pistons are furnished in standard size as well as .003", .010", .020", .030" and .040" oversizes. When necessary to replace pistons, due to wear, the cylinder walls should be honed for .003" oversize or rebored and honed for .010", .020", .030" or .040" oversize pistons. NOTE—Any time a piston is removed from the cylinder, it should be examined for carbon on the inside. Chevrolet pistons do not carbon up excessively: however, it is a good practice to inspect them and remove any carbon that is present. This helps to keep the engine oil clean. Checking Cylinders By far the best method to be used in determining the condition of the cylinder in an engine preparatory to reconditioning is the use of a dial gauge such as is shown in Fig. 2.	The dial gauge hand will instantly and automatically indicate the slightest variation in the cylinder bores. It completely eliminates uncertainty and possible mistakes in judgment. In use, the dial gauge is simply inserted in the cylinder bore, and moved up and down its full length. It is then turned spirally or completely rotated at as many points as may be desired, taking readings at each point. In this manner, all variations in the cylinder walls from top to bottom may be determined.

		Fig. 2—Checking Cylinder Sore with Dial Gouge If a master gauge, corresponding with the exact diameter of a standard size cylinder bore, is used to set the dial gauge, it is easy to determine the oversize piston to use as well as the amount of metal which must be removed from the cylinder walls to make them true. Cylinder Boring When it becomes necessary to rebore the cylinders of an engine to fit oversize pistons, the instructions furnished by the manufacturer of the equipment being used should be very carefully followed. Before using any boring bar the top of the cyl-der block should be filed off to remove any dirt or burrs. This is very important, otherwise the boring bar may be tilted which would result in the rebored cylinder wall not being at right angles to the crankshaft. In Chevrolet engines the piston clearance is provided for on the piston and this must be taken into consideration when setting the cutter in the boring bar. The piston to be fitted should be checked with a micrometer, measuring just below the lower ring groove and at right angles to the