The automobile engine
The general principles of engine rebuilding are quite similar, irrespective of the number of cylinders. Some of the more common processes of engine rebuilding are illustrated and described as they relate to the Chevrolet six-cylinder engine.
The cylinder head is left on the engine and an eyebolt is screwed into the position of the third cylinder-head bolt from the rear, on the left side, and is used for attaching to the chain hoist. After the engine has been lifted, it is placed on an engine stand or low horses or other suitable place for disassembly.
Disassembling the Chevrolet engine
To facilitate work on the engine, it should be thoroughly cleaned on its outer surfaces. An engine may be cleaned with a stiff-bristled brush and kerosene. Special cleaning solutions are quite frequently used. Socket sets or box-socket wrenches should be utilized when disassembling the engine.
The cylinder head may be removed and laid aside and the engine then rested on the top surface of the cylinder block in an upside-down position on the bench top. Other units now may be removed from it. The transmission, oil pan, engine accessories, manifold, and other parts are easily disassembled from the cylinder block. Pullers are utilized to remove the harmonic balancer and later to pull the gears.
The position of all oil lines must be carefully checked and these parts protected against any damage. As the reciprocating parts of the engine are removed, they must be laid out in order. When bearings are removed, any shims that are encountered must be maintained in their original position. All engine parts must be checked to see what their markings may be in order to facilitate reassembly.
Following, the methods of inspecting and reconditioning individual motor parts are discussed.
Check the condition of the cylinder block by means of a dial gauge. If the cylinder is found to be worn tapered or to have a piston-pin ridge near its top, recondition it, preferably by honing. If badly out of condition, rebore it with special reboring equipment. If the cylinders are honed, finish them to .003 in. oversize. If they are rebored, they should be finished to .010, .020, .030, or .040 in. oversize, these being the oversizes for which new Chevrolet pistons are regularly furnished.
Chevrolet pistons are sold with the piston-pin bushings and piston pins fitted to them. If it ig necessary to go to oversize pins, the standard oversizes are .003, .005, and .010 in. The pins are fitted by means of reaming in a special fixture. The proper fit of the piston pin is a thumb push.
Pistons and rings
Chevrolet pistons are cast iron, electroplated, and of the slipper-skirt design. They are cam ground out of round, which allows for compensation for heat expansion along the line of the piston-pin bosses. The electroplating utilized assures a satisfactory running-in period for a new or rebuilt engine.
When fitting new rings, put them in the cylinder and force them downward with an old piston for about 2 in. Measure the width of the gap between the ends of the ring. This should be between .005 and .015 in. I f less than the lowest figure, clamp a fine-cut file in the vise, and enlarge the gap by moving the ends of the ring over the file.
Check the old pistons to see that no carbon remains in the ring grooves. Roll the ring entirely around the groove. Test the fit of the piston ring with a thickness gauge. The compression rings should be fitted so that a .0015-in. feeler gauge is free, but a .003-in. feeler gauge causes a heavy drag. In the bottom or oil-control groove, provide a .002-in. free feeler or a .0035-in. heavy drag.
A piston inserter is recommended to compress the rings within their grooves as the piston assembly is forced downward into the cylinder.
Fitting main engine bearings
The main bearings are steel back babbitt-lined. The babbitt is centrifugally cast or spun into the steel lining. If for any reason it is necessary to replace the bearings, the work must he done in a shop equipped with Chevrolet main-bearing boring machinery, which is utilized to bore out the bearings to exceedingly close limits and in proper alignment of the four main bearings.
When the crankshaft is out of the engine, it is well to check it with micrometers to see whether the journals have worn out of round, tapered, or undersize to an amount exceeding .001 in. Unless wear exceeds this amount, the shaft may be continued in use. Support the crankshaft on the front and rear main bearings in V blocks, and use an indicator to check the amount of runout of both the rear and intermediate and front intermediate journals. The runout limit is .002 in.
Installing the Chevrolet crankshaft
First, clean all cuttings from the bearings and clean out all oil passages by blowing them out with compressed air. Be sure the bearing-oil passages are clear. Lubricate all bearings with engine oil and then place the crankshaft in the bearings. Next, check the end play of the crankshaft to limits indicated previously.
Install the bearing caps with four .002 shims on each side, and pull the bolts down tight. Check to see that the crankshaft rolls freely. When adjusting the main bearings, begin with the rear bearing and remove the shims evenly, that is, from each side, until a slight drag is felt on the crankshaft when it is turned by hand, with the bolts drawn tight.
Next, replace one .002 shim for clearance, and again tighten the bolts. The crankshaft should roll freely without drag. Now loosen the bolts on the rear bearing, and proceed to adjust each of the remaining bearings in turn by the same method.
The four camshaft bearings are steel-backed, babbitt-lined. They are line-reamed at the time of engine assembly. In case of damage to these bearings, they must be removed and replaced with new ones, which then are line-reamed by special equipment. If the camshaft journals exceed .001 in. out of round, replace the camshaft. If it is found to have more than .002-in. runout, straighten or replace it.
Crankshaft and camshaft timing gears
The steel gear on the end of the crankshaft is a drive or press fit. To remove it, use a gear puller. The camshaft gear is a composition gear, designed to operate with the steel so as to give long, quiet life. It is assembled on the end of the camshaft by means of special fittings and a press fit is used.
Press the gear on to allow .003 in. end clearance between the journal and the end plate. Since both gears are located to their respective shafts by means of keys, and since each gear has timing marks stamped on it, all that is necessary when timing the engine is to see that these timing gear marks are opposite each other. This, then, times the camshaft so that, as it turns in its relation to the crankshaft, the valves are opened in proper order. The backlash between the timing-gear teeth should not exceed .005 in. nor be less than .002 in.
To prevent oil leakage around the timing-gear front cover, where the crankshaft passes through it to permit mounting of the harmonic balancer, a spring-loaded leather seal is provided. See that the timing-gear cover is centralized over the crankshaft end. A special tool is utilized for this.
The ring gear used to start the engine is made of steel and is shrunk onto the outer diameter of the flywheel. Each flywheel is accurately balanced. The flywheel is located on the crankshaft flange by three dowels and is held thereto by six special large-headed cap screws which are assembled and locked in pairs.
Fitting connecting rods
First assemble the connecting rod to the piston by inserting the piston pin through the piston bosses and connecting rod, and then locking the clamp screw, with the upper end of the piston rod in the centre of the piston. Test by moving the pin sidewise to see that equal clearance is had on either side. Next, test the alignment of the connecting rod and the piston on a rod aligner to see that they are without twist or bend of the rod.
The connecting rod and bearing caps are stamped on the camshaft side with the number of the cylinder in which they are to be assembled. Stagger the piston-ring gaps so that they are equally spaced around the cylinder bore. Assemble the piston in the cylinder bore so that the pin clamp bolt is on the camshaft side of the engine.
Lubricate both the piston and the cylinder bore, and slip the piston into the bore. Bring the big end of the connecting rod to the crankpin position, lubricate the crankpin, and assemble the connecting-rod oil dipper with its mouth toward the camshaft side. Assemble and tighten the rod-bolt nuts.
Next, proceed to remove the shims, taking the same number from each side of the bearing until the rod cannot be snapped back and forth on the crankpin by hand, but can be tapped back and forth by a light blow with an 8-oz. hammer. Next, replace one of the .002-in. shims, but be careful to keep the number of shims on each side equal, if possible.
When properly fitted, it is possible to snap the connecting rods forth and back on the crankpin with one hand. Check the connecting-rod end clearance between the upper half of the connecting rod and the side of the crankpin with a feeler gauge to see that the clearance is not less than .004 in. nor more than .011 in. Finally, when all adjustments are correct, lock the connecting-rod-bolt nuts by installing new "pal" nuts, tightening them finger tight and then turning them one half turn more to lock.
Chevrolet engine oiling system
The engine lubrication is supplied by a gear pump equipped with a spring-loaded by-pass valve. The connecting-rod bearings are lubricated at low speeds by means of dippers on the rod-bearing cap which dips into troughs in the oil pan. However, at high speeds, lubrication is amply provided by oil-spray nozzles. The cylinder walls and pistons are lubricated by the oil spray thrown off by the connecting rod.
The lubrication of the valve mechanism is accomplished by oil being pumped to the hollow rocker-arm shafts. Oil pressure is directed to the four main bearings, and from the four main bearings to the four camshaft bearings in the crankcase web. The timing gears are lubricated by oil spray from the front camshaft bearing. Six nozzles are supplied in the oil pan, which are utilized to spray oil on the six connecting rods.
As the oil is sprayed off from these nozzles, the jet of oil is caught by the dippers of the connecting rod, and oil is forced into the connecting rod under high pressure. The height of the connecting-rod dippers is a very important feature, and in engine rebuilding, the best plan is to make use of the special Chevrolet tools to measure this height ; also to check the height of the oil nozzle and the depth of the oil trough. The correct aiming of the oil nozzles is tested by means of a special target gauge and water nozzle.
Oil distributor and oil pump
The oil-distributor valve assembly, is mounted on the side of the cylinder block. The oil-distributor valve is utilized to distribute the oil to the several oil passageways which carry lubricating oil to the engine.
Grinding the valves
Chevrolet valves are made from silichrome stainless steel, with the ends of the valve stems hardened electrically to reduce wear at the contact point with the rocker arm. When the engine is taken down, the valves which are removed should be thoroughly cleaned, and the condition of the valve heads and valve stems checked carefully.
The valve seat in the cylinder head is best reconditioned by grinding with an eccentric grinder. Valves may be touched up by the old process of hand grinding, but accurate reconditioning equipment, such as the grinder and refacer shown, will give better seating and' cooling, and longer valve life. In operation, the feed screw is turned to the right until the grinding wheel just clears the grinding seat. Next, balance the grinder with the compensating handle. Start the motor and feed the grinding wheel into the seat by turning the feed screw to the left one notch at a time until the wheel is grinding all' around the face of the valve seat.
When refacing the valve head, the valves are chucked in the refacing tool. While the grinding wheel is rotating at high speed, the valve, which also is rotating, is passed across the face of the stone to give a light cut all the way around on the valve face.
Chevrolet valve lifters
Push rods are made from a solid piece of steel with the two ends forged to form the contacts with the lifter and rocker-arm adjusting screw.
Assembling valves to the cylinder dead
The valve keepers are in the form of split keys which are retained by means of the spring pressure on the wedged keeper.
Installing the Chevrolet cylinder head
The cylinder-head gasket is marked "this side up." When aligning the cylinder head to the cylinder block, keep the cylinder-head gasket in place, free from damage, by utilizing guide pins. Screw these into the cylinder block at the front and rear holes on the manifold side, and guide the parts. When tightening the cylinder-head bolts, follow out the tightening diagram. If a torque wrench is used, the recommended tension is 75 to 80 foot pounds on each bolt head. Overtightening or tightening incorrectly will result in sprung heads and water leaks.
Four different types of rocker arms are used on the 1941 Chevrolet. These are the right- and left-hand angle intake valve rocker arms and the right- and left-hand angle exhaust valve rocker arms. None of these are interchangeable. When assembling these rocker arms, use extreme care to see that they are placed in the positions from which they were originally removed.
Adjusting the valves
Before attempting to adjust valves, it is necessary to normalize the engine, that is, run it at a fast idle of approximately 600 revolutions per minute, and check the oil temperature with a thermometer at the overflow pipe on the valve rocker-shaft connection. When a constant oil temperature has been reached and held for a period of five minutes, the engine has been normalized, that is, it has reached a normal temperature and is ready for valve adjustment.
This normalizing is necessary in order to bring all of the engine parts to a temperature which will eliminate all unequal expansion of parts. The next step is to lubricate all valve stems with engine oil so that they move freely in their guides, after which the valve clearance is adjusted with the intake .006 to .008 in. hot and the exhaust .013 to .015 in. hot.