1942 - 1947 Chevrolet Shop Manual



6-29

Tests show that during the warm-up period, starting with a cold engine and running idle, the following variations in valve clearance take place while the engine is warming up until the engine is normalized. These tests were made starting with the valve clearance set at—Intake .006" and Exhaust .013" Cold. Time Valve Oil Tem- Water Tem- Minutes Clearance Change perature perature Intake Exhaust Degrees F. Degrees F. 0 .006" .013" 70° 70° 3 .009" .010" 95° 125° 5 .011" .012" 115° 155° 10 .010" .012" 160° 185° 15 .0075" .0095" l80° 185° 20 .0065" .008" 190° 185° 25 .006" .012" 185° 185° 30 .006" .013" 185° 185° Covering the radiator or grille will not materially hasten this normalizing process because, even with the water temperature quickly raised to 185°, it does not change the rate at which the oil temperature increases or the engine parts become normalized. The actual temperature of the oil is not as important as the stabilization of the oil temperature. The expansion or contraction of the valves, rocker arm supports, push rods, cylinder head and cylinder block are relative to this oil temperature. Therefore only after the oil temperature is stabilized, do these parts stop expanding and valve clearance changes cease to take place, as shown in the above table. Normalizing the Engine To normalize the engine, run it at a fast idle— (approximately 600 R.P.M.) and check the oil temperature with a thermometer at the overflow pipe on the valve rocker shaft connector. WHEN A CONSTANT OIL TEMPERATURE IS REACHED FOR A PERIOD OF FIVE MINUTES, THE ENGINE IS NORMALIZED AND READY FOR VALVE ADJUSTMENT. The important factor is to eliminate all unequal expansion of engine parts before adjusting the valves, and this occurs only after the oil has reached a constant temperature. Before adjusting the valve clearance, lubricate the valve stems with engine oil to insure free movement of the valves in their guides. Adjust the valve clearance as follows:		continuous full throttle operation is required, better valve life and engine operation can be obtained by setting the valve clearance as follows: Intake .010" Hot Exhaust .020" Hot Occasionally a car or truck is brought into the service department to have the valves adjusted immediately after having been driven for some distance and the engine is already warm. The engine oil temperature under such a condition may vary considerably, depending on the type of operation and the length of time the engine has been subjected to such operation. On jobs of this kind considerable time may be saved by following the procedure described below. Run the engine at a fast idle (approximately 600 R.P.M.) and check the oil temperature with a thermometer at the overflow pipe on the valve rocker shaft connector. When a constant oil temperature is reached for a period of five minutes, the engine parts are normalized and the job may be considered ready for valve adjustment. The stabilization of the oil temperature may take place anywhere between 150° and 225°, depending on how the car or truck had been driven prior to arrival at the service department. From the foregoing it can be readily seen that the time necessary to run the engine may vary from 30 minutes in cases where the engine is started up from a cold condition, to 5 minutes in cases where the engine has already been in operation, providing the oil temperature is stabilized at the end of the 5-minute period. INTAKE AND EXHAUST MANIFOLDS The intake manifold is a "D" shape cross-section which results in better atomizing and more even distribution of the fuel mixture to each of the six cylinders. This is another contribution to smooth engine performance. The exhaust manifold is designed to reduce back pressure to a minimum. Located on the inside of the exhaust manifold is the thermostatically operated heat control valve. This valve in the exhaust manifold directs the hot exhaust gases against the center of the intake manifold when the engine is cold, as shown at the left in Fig. 65. As the engine warms up, the thermostatic spring closes the valve and directs the exhaust gases away from the intake manifold as shown at the right in Fig. 65. This thermostatic control results in the proper temperature of the incoming gases under all operating conditions. The tension of the thermostatic spring is very important—when too tight the heat will not be turned off the intake heat riser as the engine warms up.
Intake Exhaust	.006" to .008" Hot .013" to .015" Hot
On severe truck operations it is advisable to adjust the valves to the high setting, .008" and .015". In types of operation where truck engines are subjected to heavy duty service, such as log hauling in swamp country, tractor work, etc., where