1942 - 1947 Chevrolet Shop Manual



	*6-5*

	5. Expand the reamer by easy stages and repeat the reaming operation until the piston pin is fitted. The proper fit of the piston pin is a "thumb push" fit as shown in Fig. 6.	tapered one thousandth of an inch, being wider at the bottom. With this design the lower edge of the ring tends to scrape the excess oil from the cylinder wall and acts as an oil control ring until the regular oil control ring is seated (broken-in) in the cylinder. All compression rings are marked with the word "TOP" cast in the upper side of the ring. When installing compression rings, make sure the side marked "Top" is toward the top of the piston. Chevrolet piston rings are furnished in standard sizes as well as .005", .010", .015", .020", .030" and .040" oversizes. Fitting Piston Rings To properly fit new piston rings, proceed as follows: Slip the ring into the cylinder then, using the head of a piston, press the ring into the cylinder bore about two inches. Using a piston in this way will place the ring square with the cylinder walls. Now check the space, or gap. between the ends of the ring. This should be from .005" to .015". If the space between the ends of the ring is less than .005", remove the ring and try another ring for fit, or the gap in the tight fitting ring may be enlarged by the following method: Remove the ring from the cylinder. Clamp a fine-cut file in the vise. Grasping each end of the ring firmly between thumb and fingers, work the two ends of the ring across the surfaces of the file pressing the ring together at the gap lightly, until the proper space is obtained. Be careful not to distort the ring during this operation or it may bind in the ring groove of the piston. Fit each ring separately.

	Fig. 6—Fitting Piston Pin After fitting the first piston pin, the other bushings may be reamed quickly by reducing the diameter of the reamer by approximately .0005" (half a thousandth) by backing off the expansion screw. This permits quick roughing-out of all bushings, leaving about half a thousandth for the finish cut. It is good practice to check the diameter of all piston pins with a micrometer. In case there should be a slight variation in diameter, this must be taken into consideration when adjusting the reamer for the finish cut. The purpose of the reaming fixture is to make sure that the piston pin bushings will be reamed at right angles to the skirt of the piston, assuring proper alignment of the piston in the cylinder. Chevrolet piston pins are serviced in standard sizes as well as .003", .005", and .010" oversizes. PISTON RINGS The purpose of a piston ring is to take up the space between the cylinder walls and the piston, to prevent leakage of gases and oil. As these gases are under considerable pressure, it is therefore necessary that the rings not only fit snugly around the cylinder walls, but in the grooves of the pistons as well; otherwise the gases and oil will work by behind the rings. The compression piston ring used in the Chevrolet engine is designed to control oil consumption during the break-in period. The face of the ring is

		Fig. 7—Rolling Piston Ring in Ring Groove New piston rings and cylinder bores wear considerably during seating and the gaps widen quickly. Engine operation will not become seriously affected if ring gaps do not become greater than 1/32".