Aircraft technical Basics: Aircraft Propellers - Navy Training Courses Edition of 1945: Chapter 2: Two-Position controllable Pitch Propeller

HIGH-LOW

The two-position controllable pitch propeller was designed to overcome the waste of engine power which resulted with fixed pitch propellers.

An engine with a fixed pitch propeller turns at its rated rpm (revolutions per minute) when you use full-throttle in LEVEL flight. This means a loss of airplane performance under all other conditions. For instance, it means the engine is held down to about 80 percent of its normal rpm with corresponding loss of power when the airplane is taking off. Thus, an engine normally rated at 400 hp (horsepower) would develop less than 320 hp at the time of take-off. During a climb, this same propeller would hold the engine down to about 85 percent or 90 percent of its rated speed, again reducing the horsepower output of the engine and the performance of the airplane.

This loss in engine power can be reduced considerably by the use of the two-position controllable propeller which permits the change in blade pitch to be made at will. Low pitch is used during take-off and climb. High pitch is used during level flight.

The two-position, controllable pitch propeller, as its name suggests, has only two pitches-HIGH and LOW. The selection between high and low pitch is made by a hand-operated control. The low position is used when the airplane is traveling at low speeds, as in taking off and making steep climbs. In addition to the increased horsepower obtained by using low pitch, the slip of the propeller is much less when the airplane is moving slowly.

Figure 7.-Two-blade counterweight type propeller.

When the plane is cruising or traveling at high speeds, however, the pitch is shifted to high.

The three major parts of the propeller are the SPIDER, BARREL, and BLADES.

The spider is the foundation for the entire propeller-the skeleton to which the other parts are attached. Its central bore is splined-or grooved-to fit on the engine shaft. It is through these splines that the engine torque is transmitted to the propeller. The spider arms are used to support the blades and provide a smooth surface on which the blades turn. Thrust and torque loads are absorbed by the spider arms. I

The barrel of the propeller houses the entire hub mechanism and holds the blades on the spider arms. It is supported on the spider by means of micarta (plastic) blocks located between the spider arms. The shoulders of the barrel fit over the outer bearing races of the blades and absorb the centrifugal force on the blades.

Figure 8.-Three-bladed counterweight type propeller.

You remember that centrifugal twisting force is acting on the blades tending to force them into low pitch. However, it is possible to reverse this tendency by adding COUNTERWEIGHTS to the blades. By means of the counterweights, the entire blade and counterweight assembly will have a tendency to go into high pitch.

The pitch changing mechanism is operated by a CYLINDER fitted on a PISTON (propeller shaft extension) between the counterweights,

You have a photograph of the pitch-changing assembly in figure 11.

The cylinder carries RODS, or arms, projecting f rom it, called COUNTERWEIGHT BEARING SHAFTS. These pass through slots in the counterweight brackets, and change the reciprocating motion of the cylinder into the rotary motion of the brackets and blades.

Figure 1l.-Pitch-changing assembly.

The cylinder rides on the piston gaskets at the outboard end of the piston. The inboard end of the cylinder incorporates a micarta chafing ring to prevent galling.

The piston screws onto the end of the propeller shaft. With the front cones, it acts as a retaining nut for the propeller.

HOW IT WORKS

The are TWO forces that make it possible to change blade pitch-centrifugal force and hydraulic pressure. Oil pressure changes the blade angles from high to low pitch, whereas centrifugal twisting force changes the blade angles from low to high by acting on the counterweights attached to the blades.

When the control is set for low pitch, a threeway valve is turned so that it connects the engine oil-pressure line with an oil line leading to the pitch-changing cylinder. Oil immediately starts flowing through the valve, through a collector ring, into the inside front end of the crankshaft, and then into the pitch-changing cylinder.

Figure 12-Principle of operation two-position controllable-pitch propeller.

The incoming oil forces the cylinder to move f orward on a stationary piston. This movement of the cylinder rotates the blades to low pitch position.

Remember, it is the oil pressure in the propeller cylinder which holds the blades in low pitch, and prevents the pull of the centrifugal force on the counterweights from rotating them to high pitch.

Suppose you want the blades at high pitch again. You set the Control to HIGH, and, presto, the three-way valve turns again. In this position, it connects the propeller line to a drain so that the oil flows out of the pitch-changing cylinder. Centrifugal force goes into action, and the counterweights move outward. Down goes the cylinder against the piston, and the blades rotate into high pitch position.

Take a look at the cutaway sections of the pitch-changing mechanism in figures 13 and 14. Here you see the vital parts of a pitch-changing cylinder and piston for a two-bladed propeller of the counterweight type. They are approximately the same as for a three-bladed propeller except, of course, that three counterweights are used on the three-bladed type. The principle of pitch-changing operations is the same, however, for both two- and three-bladed propellers.

Figure 13 shows the mechanism with the control set for low pitch. The cylinder has moved up on the piston, and the part of the cylinder above the head of the piston is filled with oil.

Notice the CAM SLOTS at the left and right of the Cylinder. The movement of the cylinder FORWARD on the piston moves the counterweight bearing shafts forward, which in turn move the counterweight brackets forward, thus putting the blades into a lower pitch.

As the counterweight bearing shafts move in the counterweight-bracket cam slots, they turn the brackets. The brackets are attached to the blade bushings by index pins. So, as the brackets turn, the blade is also turned, and the pitch is changed.

In figure 14, you have turned the control to high pitch. The oil has run out of the cylinder, which

Figures 13 and 14.-Cutaway of pitch-changing mechanism.

is now resting on the piston. - The downward movement of the cylinder has allowed the shafts to move down to the bottom of the cam slots, and has freed the counterweights so that they swing out as the blades revolve.

Here's the whole story in a nutshell. FILLING the cylinder with oil holds the counterweights FORWARD and keeps the blades at low pitch. Draining the oil from the cylinder allows the counterweights to swing inboard, and this turns the blades to high pitch.

REMOVAL

There's no need to tell you how important it is that every part of the propeller be in perfect condition. A flaw or neglected repair is the first step towards DISASTER. Careful, thorough inspection of propeller parts is the first step in PREVENTION. Before you can inspect propeller parts, however, you have to know how to remove the propeller from the crankshaft, and how to disassemble it.

Four steps are used in removing the propeller from the crankshaft.

First, disengage the cylinder head lock wire and remove the cylinder head. Have a pail handy to catch the oil from the piston gasket nut.

Then disengage the piston lock ring. You do this by removing the cotter pins. It is good practice to slide the lock ring up on the piston and safety it there.

Then unscrew the piston. This will start the propeller off the engine shaft.

Finally, slide the propeller slowly forward on the engine shaft and remove. Take care not to damage the engine shaft threads. And take care, on Wright engines, not to hit the oil supply pipe.

DISASSEMBLY

You have the propeller free now. Here's how you disassemble it.

Unscrew the counterweight caps, and record the position of the adjusting nuts with relation to the scale stamped on the counterweight face. Remove the adjusting screws. Take off the counterweights and remove the counterweight bearing shaft pins. Unscrew the counterweight bearing shafts and remove counterweight bearing assemblies with spacers.

Be careful that the oilite thrust washers do not fall. Disengage the snap ring from the spider groove, and lift the piston-cylinder assembly. Make sure that the cylinder bearing shaft thrust bearing assemblies do not fall out of the cups of the counterweight bearings shaft bushings and that the split front cone does not slip off the piston. Remove the barrel bolts, and split the parting of the front and rear halves of the barrel, using a brass or aluminum wedge.

Now you're ready to drift off the front half of the barrel. Take care to keep the arms of the brackets turned so that they do not touch the barrel as it is drifted up. Then drift off the rear half of the barrel. Hold the thrust retainers in place or they will fall when the rear half of the barrel drops off. Wrap the blade shanks with cloth to prevent the steel thrust races from marring or other injury. Remove the alemite fittings. This will make it easy to pull off the blades. Remove the oilite shim plates and brass shims. Keep them in PAIRS, marked so that they may be reassembled on the proper spider arms unless the brass shims need replacing. Remove the micarta barrel supports and the leather grease retainers. Note and record the location of the brackets on the blade bushings, then remove the brackets from the blades. Take care that the index pins are not lost when the brackets are drifted off the blade bushings.

With that step you have completely disassembled the propeller and it is ready to be cleaned, inspected, overhauled, and assembled. Of course, all this isn't as easy as it sounds. It takes a good man considerable time to get the work done right.

INSPECTION AND REPAIR

One of the most common propeller ailments is the leakage of engine oil from around the cylinder head, from between the piston and cylinder, from around the front cone, or from the rear of the barrel. You can be pretty certain that such trouble is caused either by loose-fitting working parts, or by loose, worn or damaged gaskets or -washers. Correction of oil leakage depends, therefore, on checking the fit of the parts around which the leak occurs, and checking washers and gaskets in the vicinity.

The time between propeller overhauls cannot be set definitely. It depends largely upon the type of operation and maintenance given the propeller. In general, however, propellers should be changed whenever the engine is changed, the overhaul period being the same for both. And that holds good for ALL types of propeller.

The following chart will give you some idea of the type of defects to watch for when you inspect the propeller, and indicates what's to be done about them.

The following parts are expendable. Occasionally they can be reinstalled, but it's usually best to discard them and put new ones in their places.

Cylinder head gasket.
Inboard and outboard piston gaskets.
Cylinder bearing shaft bearing retainers.
Counterweight bearing shaft assemblies.
Front cone packing washer.
Brass torque shims.
Counter weight bearing retainers.
Oilite thrust washers, cotters, lock washers.

ASSEMBLY

More than 30 separate steps are involved in assembling a controllable pitch propeller, but the process isn't as complicated as it may sound. Before you study the method of assembly, however, there are some things to remember.

The propeller is a carefully designed instrument, machined to close tolerances and subject to accurate adjustments. Therefore, make it a rule to be especially careful to avoid even the slightest damage to parts in handling and assembling them.

For instance, metal bearing races on blades should be wrapped in cloth to keep them from marring or injuring the blade shanks during assembly. Avoid marring or scratching the parting surfaces of the barrel. Handle every bearing surface as carefully as watchmakers handle the delicate parts of a watch. All propeller parts must be absolutely clean and free from grit before being assembled. Bearings should be examined for perfect smoothness, and all friction surfaces should be coated with light oil or grease.

In most cases Navy propeller parts are numbered, so that when two or more pieces have to go together, you can match them up "by the count." For instance, when you assemble the counterweight brackets on their blades, you can check the bracket numbers and blade numbers to make sure you get the correct ones together. Similarly, when a part like a ball-bearing race has to be lined up with a blade, you'll find guidance marks to help you aline them.

Start the assembly of the propeller by placing the spider accurately and firmly in position. It's well to remember that UNLESS THE SPIDER IS RIGHT, THE PROPELLER WON´T BE RIGHT. If you give careful attention to this, you'll save yourself a great deal of trouble.

Now you can take up the assembly of the propeller, step-by-step.

Place the splined bushing on the spindle of the checking table. Put the rear half of the barrel over the spindle and splined bushing. Slide the spider down on the splined bushing and coat the spider arms with grease. Place the brass torque shims on the shoulder at the face of the spiderarms and the oilite shim plates on the spider arms against the laminated shims. The leather grease retainers should be placed in the fillet at the base of the spider aims. One face of the grease retainer is turned to fit this fillet.

As you've already learned, you should wrap the blade shanks with cloth to prevent the steel thrust races from marring or injuring them. Assemble the blade brackets on their correspondingly numbered blades, being sure that four index pins are used for each blade. If the propeller has just been received from the factory, fill the blade bush ings with grease to within 2 inches of the top. But if the propeller is being assembled after an overhaul and its balance must be checked, leave the blade bushings DRY.

Install the micarta barrel supports. After making certain that the alemite fittings have been removed from the spider, shove the blades on their correspondingly numbered spider arms. If the propeller has just been received from the factory and the blade bushings have been filled with grease, the excess grease will be forced through the open alemite fitting holes. Extensions, made from 1/8-inch pipe and threaded on one end, should be used to lead this excess grease through the micarta barrel supports.

Screw in the alemite fittings and then cover the blade thrust bearing races and retainers with a thin coating of "Mobilgrease" #2, or its equivalent.

Place the thrust bearing retainers in position between the thrust races and aline the etched "O" on the inner thrust race with the stamped "O"  on the blade shoulder.

Now, lift the lower half of the barrel up of the spider blade assembly so that it starts evenly on all three outer thrust races. Make sure that the numbers on each arm of the barrel correspond with the blade numbers. Using a rawhide mallet, tap the lower half of the barrel up into place on the assembly. Then place the front half of the barrel over the counterweight brackets and tap down in place. Make sure that the numbers on each arm match the corresponding blade numbers. You'll have to rotate the brackets in order to fit the front half of the barrel in place. Keep the brackets clear of the barrel as it is tapped home. Install and tighten the barrel bolts in their respectively numbered holes. Use a wrench having not more than 14 inches leverage.

EXCESSIVE TIGHTENING OF THE NUTS MAY CAUSE FAILURE OF THE BARREL BOLTS.

At this point, you should check the tightness of the fit of the blades in the hub assembly. This is done by measuring the amount of torque or twist necessary to turn each blade.

Using a lever arm clamped to the blade and a set of spring scales attached to the other end of the lever arm, apply sufficient pull on the scales to turn the blades. This pull (in pounds) multiplied by the length (in f eet) of the lever arm is the torque (in units called foot-pounds).

Check the latest Service Bulletin or Technical Order to be sure of the proper torque.

If the torque on any of the blades is not correct, the propeller MUST be disassembled again. Corrections are made by inserting the proper sized brass torque shims. Never make an attempt to reduce the thickness of the oilite shim plate to obtain the correct torque.

Assemble the cylinder and the split front cone with a dummy piston, and put in place on the hub assembly.  Be sure that the numbers on the cylinder arms correspond with the bracket numbers. The regular piston has a small hole at its base for the oil supply pipe. This hole is too small to permit the spindle or the mandrel to pass through, hence the necessity of using a dummy piston during assembly. This may be another piston in which the base has been cut out sufficiently to allow the mandrel to pass through.

Tighten the dummy on the splined bushing. Place the cylinder-bearing-shaft thrust-bearing assemblies in the cup-shaped counterweight-bearing-shaft bushings. The race with the smaller inside diameter is the INNER race, and should be installed in the cup-shaped bushing first. Install the counterweight bearing races and retainers. Slip the oilite thrust washers between the outer races of the cylinder-bearing-shaft thrust-bearing assemblies and the brackets, and tighten the counterweight-bearing shafts in place. Be sure that the numbers of these shafts correspond with the numbers on the cylinder arms.

Place the inboard (long-flanged) and outboard (short-flanged) piston gaskets on the piston and secure them in place with the dummy piston gasket nut. Fasten the counterweights on their respectively-numbered brackets, and install the adjusting screws in the counterweight slots. Then screw on the correspondingly-numbered counterweight caps.

The propeller is now ready to have its angles checked. The full high and low pitch angles should always be checked to make sure that the brackets have been indexed correctely on the blade bushings.

Fill the propeller blade bushings with grease. This should be done by disassembling the propeller, taking the blades off the spider arms and filling them to within 2 inches of the top with "Mobilgrease" #2 or its equivalent. This procedure eliminates the possibility of air pockets forming in the blade bushings and spider arms. Finally, reassemble the propeller.

The regular 20° piston (with snap ring and split front cone) may be assembled in the propeller in place of the dummy piston provided the splined bushing is shimmed up high enough to prevent the spindle of the table fixture from touching the base of the piston when the piston is tightened on the splined bushing. After you have installed the inboard (wide flange) piston gasket, the propeller will. be ready to be placed on an engine crankshaft.

Shift the blade angles by moving the cylinder up and down. This will aline the piston-cylinder assembly. When you have everything in order, and are ready to place the propeller on the crankshaft, always take one last look to make sure that all of the threads on the outside of the crankshaft and inside the propeller mounting assembly are straight, undamaged, and are not burred or pulled. CHECKING EVERY THREAD SHOULD BE A HABIT IN ALL PROPELLER ASSEMBLY WORK.

Be dead certain that all threads are in perfect alinement before starting any threaded part into place. Don't ever use force to tighten a piston or any similar part, if there is any binding or resistance between threads. And always be positive that there are no crossed threads.

And, incidentally, DON'T decide that if threads are damaged, all you need to do is rechase them. On many parts of a propeller, the relative pitch diameters are such that the threaded pieces are not firmly clamped together unless the threads are cut to their proper tolerances. Make it a rule, therefore, to consult approved service literature (or a propeller specialist) before you rechase any threaded part of a propeller.

You'll find that certain details of propellerassembly will depend on the make of engine to which it eventually will be attached. Some engines, for example, require a gasket (packing) under the oil supply line of the propeller. Others do not. On Wright engines you have to screw the oil supply pipe into the oil plug hole, which is inside the crankshaft. On the other hand, Wright engines do not require packing washers on the front-propeller cone as some other makes of engines do.

Most Wright engines have a CRANKSHAFT VENTILATION or BREATHER SYSTEM, while Pratt and Whitney engines have a BREATHER SYSTEM which is ventilated through the crankcase. Fundamentally, the CRANKSHAFT BREATHER is just what the name implies - a unit which allows the engine to "breathe." It is a hollow crankshaft that exhausts internal engine gases through the front end of the crankshaft. This makes it necessary to design a different type of propeller oil-supply assembly than is used in crankcase-breather engines.

The crankshaft-breather unit consists of a piston having drill holes through the wall at its inboard end to permit the crankcase gases to escape. A direct oil line conducts the oil through the center of the crankshaft, then through the piston to the other side of the piston head. A solid plate, through which the oil pipe extends, prevents the oil from flowing back into the piston. This plate serves as a retaining nut on the piston gasket, and also as an oil-supply retainer inside the cylinder.

The breather unit (used with engines that breathe through the crankcase) consists of a piston without drill holes. Oil, flowing from the crankshaft, fills the entire piston up to the cylinder head. An oil pipe is not needed because there are no gases to contend with. - There is, however, the possible chance of oil seeping between the inside diameter of the piston and outside drain of the crankshaft. A packing washer is added to the front cone to prevent such leakage. This necessitates an extra groove in the front cone to allow for the placing of the packing washer.

In some engines, an AIR-SEPARATOR PLUG is used. This plug allows any air that may collect at the center of the shaft after propeller installation to be bled from the system through a drain.

On certain propellers, the same type piston is used REGARDLESS of whether or not the engine breathes through the crankshaft. In these installations only the oil supply pipe is changed. In a Pratt & Whitney engine, the oil is supplied by a packing expansion plug with an oil pipe, joined to the piston through a packing gland at the inboard end. The Wright installation consists merely of a short extension of the oil supply pipe which joins the piston through the same packing gland.

To help the piston function as a retaining nut for the propeller, a front cone is attached by a groove to the bottom flange of the piston. The cone fits firmly against the front cone seat of the spider.

BALANCING

You probably remember as a youngster what happened when you got a bad balance on a seesaw-either you sat suspended in mid-air, or came down to earth with a bang. Something like that can happen in the assembly of propeller parts, too. Unless it's balanced properly, your propeller, like the see-saw, will play some tricks. To obtain correct blade angle settings and BALANCE, make sure the propeller spider is accurately located and firmly held on a bushing.

Best way to accomplish this is to use a splined bushing whose measurements are identical to those of the engine crankshaft. This bushing is inserted in the spider. When a piston with split front cone is tightened on the bushing, the front cone and rear cone are firmly seated in the ground tapers of the spider.

Figure 15.-Splined bushing and mandrel assembly. (Two views.)

The splined bushing, such as you see in figure 15, has a centering hole which fits either the spindle of the checking table or the mandrel used for balancing. This combination of piston, split front cone, spider, splined bushing, rear cone, and spindle (or mandrel) insures the elimination of any play and assures you of accurate blade settings and propeller balance.

To obtain DRY BALANCE, here are the steps you should follow.

Coat the bearing surfaces and shim plates with a light film of grease. Completely assemble the propeller on the splined bushing and checking table, except for the cylinder head. Shift the

Figure 16-Typical balancing stand and propeller.

blades to high pitch and check each blade angle at the 42-inch station to make certain they are all approximately the same. Remove the propeller from the checking table and insert the mandrel in the splined bushing. Then place the propeller on a specially designed balancing stand, as in figure 16. Make sure the room is free of air currents, and the balancing stand is true. Otherwise you won't get accurate results.

Check each blade in a horizontal position. The propeller must not show any tendency to rotate. On 2-way propellers only, check the vertical balance with the blades perpendicular to the plane of the knife edges. There should be no tendency for the propeller to rotate. Three-bladed popellers don't get this check-up.

Horizontal balances can be equalized by inserting lead wool in the hollow barrel bolts on the light side of the assembly or removing lead wool from the barrel bolts on the heavy side. In case this is not sufficient, the propeller should be disassembled and balancing washers added or removed from the blade plug of the light or heavy blade. The propeller should then be reassembled, and the high and low pitch angles set accurately. After setting the blade angles, fill the propeller with grease and obtain the final balance. This is known as WET BALANCE. It is accomplished by adding grease to the light blade.

The angle at which the counterweight brackets are attached to the blades serves as the base or index setting for BLADE ANGLE ADJUSTMENTS. Blades actually do not maintain the same angle throughout their length, but vary from shank to tip because of their built-in twist. The "blade angle" is considered to be the angle of the blade at 42 inches radius. On the E and D shank blades in figure 17, the counterweight brackets are indexed to the blades by means of index pins (four for each blade) which fit in semicircular holes in the brackets and corresponding holes in the blade bushings.

On the B shank blades the brackets are indexed to the blades by keys (two for each blade), also illustrated in figure 17.

The E shank blade is shown with its counterweight bracket indexed to a base setting of 23°. The semicircular holes in the bracket are numbered, and the holes in the blade bushing have corresponding numbers. These numbers indicate BLADE ANGLE at 42 inches radius. To index, move the bracket around on the butt of the blades until the desired numbers coincide. Then insert an index pin at that point and additional pins at the three other points where the holes coincide (90° apart.) When you're facing the butt of the blade, the base setting IS INCREASED one degree by placing the index pins in the next set of semicircles to the LEFT. If they are placed in the set of semicircles immediately to the RIGHT, the base setting is DECREASED one degree.

Always use the index pin to aline the semicircles on the bracket and bushing whose numbers correspond to the desired base setting. This base setting is stamped on the lead fillet of the counterweight, and should be CHANGED to correspond with any relocation of the index pins.

INSTALLATION

If it's your job to put the propeller assembly on the nose of the airplane, here's how you go about it. Remove the screw plug from the propeller oil feed line inside the crankshaft. Install the correct engine shaft oil plug or oil supply pipe. Dress off all corrosion, galling, scores and scratches on the crankshaft and install bronze rear cone on engine shaft, against the thrust nut.

Now install the split front cone on the propeller piston. The cylinder and piston should be removed from the propeller for this installation, because the front cone cannot be installed without moving the cylinder out toward low pitch, and any movement of the cylinder before the piston is screwed on the crankshaft, tends to cock the assembly. This makes it difficult to start the piston on the crankshaft and may cause damaging to the crankshaft threads.

The cylinder and piston can be removed by unscrewing the counterweight caps, taking the adjusting screws out of the cams in the counterweights, removing the counterweights, and unscrewing the counterweight bearing shafts. Be careful in removing the adjusting screws not to disturb the position of the nuts.

Oil the crankshaft and rear cone. Then, put the propeller on the crankshaft. Assemble the cylinder, piston, snap ring, and front cone. When placing this assembly on the crankshaft, be sure that the numbers above the cylinder bearing shaft bushings correspond to the adjacent counterweight brackets. Next, screw the piston on the crankshaft, making SURE that the piston and crankshaft threads are in perfect alinement. NEVER USE FORCE to tighten the piston if there is binding or an indication that the threads are not properly started. If you do, you'll have serious trouble on your hands. As the piston is turned on the crankshaft, the oil supply pipe in the engine shaft is forced through the gasket at the base of the piston.

Tighten the piston on the crankshaft. Use the propeller wrench and a bar about 4 feet long, and apply a force of approximately 180 pounds at the end of the bar. To make certain the piston is being pulled home, the bar should be rapped once on the section next to the wrench. Use a normal swing with not more than a 2 1/2-pound hammer, and strike the blow while force is being exerted at the end of the bar. This operation should be repeated after the first flight, and another check made at the end of 25 to 50 hours to see that the piston is tight.

CAUTION-DO NOT ATTEMPT TO TIGHTEN THE PISTON BY HAMMERING ON THE END OF THE BAR.

Snap the snap ring in place, and install the two piston gaskets (the one having the longer flange is the inboard gasket). Install the counterweightbearing-shaft thrust-bearing bushings. This assembly consists of two circular races and a ball-thrust retainer. The race with the smaller inside diameter is the inner race, and should be installed in the cup first.

Place the counterweight bearing races, retainers, and cap races in the brackets. Slip the circular oilite washers between the outer race of the cylinder-bearing-shaft thrust-bearing asseniblies and the arm of the brackets. Screw the bearing shafts in their corespondingly numbered holes. It is essential that the grooves in the counterweight races match the bearings in the counterweight retainer. The curvature of this bearing is gradual. To make positive that the cap races are not assembled upside down, an arc is stamped on the outer face, indicating the direction of the bend in the grooves. After the bearing shaft has been screwed up tight, this arc should be checked.

Lock the bearing shafts in the cylinder with the bearing shaft clevis pins, and cotter the pins. Slip the spacers into place in the counterweight bracket slots, and assemble the counterweights, making sure that the number of each corresponds to its bracket. Install piston gasket nut and tighten. Use a bar approximately 2 feet long with the wrench. Place the cylinder head gasket on the cylinder bead. A light, coating of grease will hold this gasket in place.

Now screw the cylinder head on the cylinder. This should be tightened with the bar used on the piston gasket nut. Lock the cylinder head with its lock ring. Place the adjusting screws in the counterweights, being CAREFUL not to disturb the adjusting nuts. Screw the counterweight caps, making SURE that the number on each corresponds with its bracket. Put in the counterweight cap clevis pins and cotters. Then, as your FINAL STEP in installation, check all lockwires and cotters.