Section 6 - Engine

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.
NOTEŚReplace 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.
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.
NOTEŚAny 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. 2ŚChecking 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





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