ENGINE BLOCK COMPONENTS

1. Crankshaft

The crankshaft must be handled with extreme care to avoid fracturing or otherwise damaging the finished surfaces. Damage to these surfaces will cause rapid wear of bearings and seals, resulting

in engine failure soon after the rebuild is accomplished. Your first step is to clean the crankshaft. The crankshaft may be cleaned with cleaning solvent or a strong parts cleaner if the solvent cannot do a thorough job. After the initial cleaning, use an air hose to blow out the small passages in the shaft. These are oil passages and they are vital to the life of the bearings. Once the crankshaft has been thoroughly cleaned, inside and outside, inspect it visually for cracks, burrs, and grooves. Cracks, if present (and sometimes they are hard to find) are a sign of metal fatigue; therefore, the crankshaft should be discarded and a new one obtained. If you locate burrs on the finished surfaces, you can usually eliminate them with the oil stone. If grooves or deep nicks appear on finished surfaces, the crankshaft must be ground on a lathe to a smaller size if possible. Consult the machine shop personnel concerning the grinding of the crankshaft. If they cannot do the job, discard the crankshaft and obtain a new one through the supply system. Assuming that you have inspected the crankshaft and found no major defects that could not be remedied with the oil stone, take some measurements to make sure that the crankshaft main journals and the crankpins are not out-of-round. An out-of-round journal or crankpin is just as bad as a burr, nick, or groove. Each journal and crankpin must be measured across its diameter in two places at 900 angles to each other. Make these measurements with an outside micrometer by adjusting the micrometer until it may be passed across the journal with a very slight drag. This is illustrated in below. The size of the circle is not necessarily the size of the journal or crankpin. The arrow to the right indicates the directions in which the micrometer is moved.

Measuring crankshaft main journals and crankpins for out-of-round with a micrometer.

Before attempting to use the micrometer, be thoroughly familiar with its care and use. TM 9-243, Use and Care of Handtools and Measuring Tools, provides good basic information that will enable you to properly use this measuring tool. If the main journals and crankpins are found to be out-of-round, they must be ground or the shaft should be discarded. Before having the crankshaft ground, make sure the shaft is worth grinding. What if it is not aligned?

A warped crankshaft is of no value to you in the rebuild or repair of an engine. With a pair of "V" blocks that may be fabricated locally and a dial indicator gage, you can determine the runout (warpage) of the crankshaft by placing the gage point on the crankshaft journal and rotating the

crank illustrated below.

Measuring crankshaft runout (warpage).

If the crankshaft is found to be warped, replace it with a new shaft. If there is no warpage, check the woodruff key slot at the end of the crankshaft. Sometimes this slot will become enlarged. Make sure the woodruff key fits snugly into the slot; and while you are checking the key fit, check the key itself for burrs and nicks. Most of these may be eliminated with an oil stone. Just be careful that you do not decrease the size of the key when eliminating these defects. Now, let's clean the main bearings thoroughly and inspect each bearing half. Scored or chipped bearings as well as excessively worn bearings must be replaced. At this point, you may begin to eliminate crankshaft end play if it was found to be excessive during disassembly. This is done by replacing the main thrust bearings. You must determine whether or not the bearing halves fit the crankshaft properly. This may be accomplished by two different methods. First, let's study the telescopic gage method. The use of these measuring devices requires skill and knowledge of their functions and must be learned from an experienced mechanic if an accurate reading is to result. Basically, the measurements are

taken at six points in each crankshaft bore with the telescopic gage shown in figure below.

Measuring the crankshaft bore with a telescopic gage.

Measure each bore near both ends to determine the taper of the bore. Each end is measured across the bore at a right angle to the split of the bearing halves, then at two other points 450 from the original measurement. These measuring points are illustrated in figure below.

Points of measurement for crankshaft main bearings.

Note that the illustration indicates that the end measurements are taken 1/4-inch in from each end. This is an approximate figure. Check your TM for specific distance. After EACH use of the telescopic gage, such as measuring point "B," a micrometer must be used to measure the telescopic gage length since it has no measurements on it. When all measurements have been taken, subtract the corresponding crankshaft journal measurements. The difference found between these measurements is the running clearance of the main bearings, which must be compared with the specifications listed in the TM to determine whether the bearings are suitable for use. Note: To obtain accurate measurements, the bearing caps must be torqued to the specified torque listed in the TM. Another method of determining running clearance is the plastigage method. Plastigage is a commercial name that has been accepted as a common term in the automotive field. It is a small string of plastic material packaged in a strip of paper. The paper is used to take the measurements as well as to protect the material. When using plastigage, the contact areas must be clean and dry, the crankshaft must not be rotated, and all caps must be installed and tight. Turn the engine upside down. Place the crankshaft in its proper position in the main bearing frame with the upper crankshaft bearing halves installed. Then, place a small strip of the plastigage along the length of the journal. Place the lower crankshaft main bearing half inside the main bearing cap. Install the main bearing cap and tighten it to specified torque. After you have

done this, remove the bearing cap and measure the flattened strip against the paper gage provided

in the package.

Measuring crankshaft bearing running clearance using plastigage.

Plastigage may be obtained in three ranges. The color of the plastic string indicates the range as follows: Green is for bearings requiring 0.001 to 0.003 inches, red is for bearings requiring 0.002

to 0.006 inches, and blue is for bearings requiring 0.004 to 0.009 inches running clearance. Check your TM specifications before obtaining the plastigage to ensure that you are using the correct

type. Now, install the crankshaft timing gear and you are ready to proceed to the next component. Drive the woodruff key into the woodruff key slot and slide the gear onto the shaft with the timing mark visible from the front of the shaft. Let's see what you've learned so far. What precision tool is used to measure a crankshaft for out-of round? If you said a micrometer you are absolutely right. And what precision tool is used to check the crankshaft for warpage? That's right, a dial indicator. With all repairs completed on the crankshaft, the next component that you have to be concerned with is the flywheel.

2. Flywheel

Inspect the flywheel thoroughly for scoring, cracks, and heat checks (discoloration due to extreme heat). If any of these defects appear, replace it with a new one. Now, inspect the flywheel ring gear for worn, chipped, or cracked teeth. In most cases, this will be cause for discarding the flywheel. However, in some cases you might be required to replace only the ring gear. If you must replace the ring gear, cut the defective gear off with a chisel and cool the flywheel to the lowest temperature possible within your means (this may be room temperature or lower). The new ring gear must be heated to approximately 6000 Fahrenheit. Cooling the flywheel and heating the ring gear aides in the shaping and bonding of the two pieces.

In some cases, the clutch pilot bearing is installed in a bore located in the flywheel and, in other cases, it is installed in a bore located in the rear end of the crankshaft. In either case, force the pilot bearing into its bore and make sure it is snug and properly aligned. In the case of a bronze bushing-type bearing, you should always install a new one. In the case of ball or roller type bearings, make sure the bearing is operating smoothly. If the above defects are not corrected, poor clutch engagement results as well as the destruction

of the clutch components in many cases.

3. Vibration Damper

Now, inspect the vibration damper for chips and cracks. Chips will result in vibration due to an unbalanced condition and cracks will result in the eventual destruction of the damper and possible damage to other components. If the damper is the type discussed earlier in the course, with the rubber mounting between the wheel and outer ring (weight), inspect the rubber for deterioration. The deteriorated condition can cause damage. If any defects are apparent in the vibration damper, discard it and obtain a new one.

4. Piston Assembly

Although the piston assembly performs a relatively simple function, the specifications are quite critical due to the speed that the piston travels, the pressure exerted on it, and of course the

resulting friction. Keeping this in mind, let's begin the repair of the piston assembly. To repair the piston, it must first be disassembled. To prevent damaging the piston's surface, cover the vise jaws with a soft material illustrated below. Soft tin or aluminum covers should be available in every shop. If not, you may fabricate a pair. With the jaws of the vise covered, secure the connecting rod of the piston assembly in them. With the piston secured in the vise, remove the rings the shortest distance off the piston to prevent damaging the piston surface. Ring expander tools provided for this purpose will prevent scratching and burring the piston. Figure shows tools commonly used in the removal and installation of piston rings. Any of these tools may be used on any type of piston.

Secure piston in vise.

Common ring expander tools used to remove and install piston rings.

After all the rings have been removed, the oil control ring expander must also be removed. In most cases, the oil ring, as well as the expander, must be removed by hand. Extreme caution must be exercised to prevent scratching the piston during this procedure.

To prepare for the next disassembly step, mark the piston and its connecting rod to ensure that the same rod and piston are kept as a set. The piston pin must also be included in the marking. Piston pins are NOT interchangeable. Interchanging piston pins usually results in a piston pin knock (loose pins). You are now ready to remove the piston pin, separating the piston from the connecting rod. Some pistons may require heating and having the pin pressed out while others may have piston pin retainers. Consult the appropriate TM for the proper piston pin removal procedure. Again, exercise extreme caution to prevent damage. Remove the connecting rod. Mark the connecting rod and piston pin to ensure their return to the original piston. Lay the separated piston and connecting rod on a clean surface and repeat the same procedure with the remaining pistons. Once the pistons are disassembled, clean and inspect them. The best method of cleaning them is

by dunking them in cleaning solvent and using a brush to remove the carbon deposits on the head of the piston ONLY. The ring grooves must be cleaned also. Special tools are designed for this purpose, but if none are available, an old ring may be used provided the edges are not sharp enough to scratch or burr the piston. Figure illustrates the use of a piston ring groove cleaner. The tool is held in its track in two places by the guide, and the blade cuts the carbon away as it is rotated around the piston.

Cleaning piston ring grooves.

After cleaning the grooves, blow the piston clean with a compressed air hose, making sure all holes are completely clear. When this is accomplished, inspect the piston thoroughly for scoring, burrs, and cracks. Light scores and burrs may be eliminated with crocus cloth, after which the piston is again serviceable. However, if all scores and burrs cannot be eliminated, discard the piston and use a new one. Cracked pistons must be discarded. Before continuing let's review what you've learned. How would you repair a lightly scored piston? Crocus cloth is correct. And what must you do if the crocus cloth is unable to remove the scores? That right, you must replace the piston. After repairing or replacing defective pistons, you must be certain that they are going to fit properly into the cylinders. The next step is to check this piston fit. Both the piston and the block must be at room temperature to make this measurement, and the piston and cylinder walls must be clean and dry. With the piston properly fitted, you must now select the proper piston rings. New rings must be used. These rings must fit both the piston and the cylinder. First determine whether they fit the cylinder. Select a compression ring from each set and place it inside the cylinder. This may be done by pushing the ring down into the cylinder with the head of

the piston. With a feeler gage, determine the gap between the ends of the rings.

Measuring piston ring gap

If the ring fits the cylinder bore properly, see if it also fits the piston properly. You know that it will fit around the piston, but will it be loose in the groove? To determine this fit, insert the ring in the groove for which it is intended and check the clearance with a feeler gage. This is known as piston ring side clearance. Now, match your findings with the manufacturer's

specifications.

Measuring piston ring side clearance.

With all the pistons repaired, let's begin work on the connecting rods. Clean the connecting rod in cleaning solvent; probe the oil passage and squirt holes with soft wire; and, blow loose foreign matter out with an air hose. Clean the rod bearings also. You must make a thorough inspection of the connecting rod and bearings. Begin with the connecting rod bearing cap and saddle. Check for scuffing, pitting, and burring. Slight imperfections may be removed with crocus cloth or a fine stone. If they cannot be removed, the rod and cap must be replaced. Check the condition of the connecting rod bearing and the piston

pin bearing. If excessive wear or pitting is evident, discard these bearings. If the piston pin bearing appears serviceable, check the piston pin fit. This may be done by measuring the inner diameter of the piston pin bushing (bearing) with a T-gage and the

outer diameter of the piston pin with a micrometer.

Measuring piston pin bushing (bearing) with telescopic gage.

Measuring outer diameter of the piston pin with a micrometer.

If the piston pin bushing is worn excessively, it must be removed and a new one installed. This should be done with an press. Figure below illustrates the use of the press to install the new bushing. Removal is similar to installation. Installing a new bushing does not necessarily mean that it will fit the piston pin. Again check the inner diameter of the piston pin bushing and match it against the outer diameter of the piston pin.

Installing piston pin bushings.

With the piston pin bushing checked, and replaced if necessary, place the connecting rod bearing halves in the connecting rod saddle and cap and bolt the two together. Now check out-of-round

and taper of the connecting rod bearing. To determine this, measurements are taken in two places at each of the connecting rod bearing bore, just as you did with the crankshaft main bearing bores. On each end of the bore, take a measurement with a telescopic gage and micrometer in direct line with the connecting rod and another at a 900 angle to the connecting rod. The difference between these measurements gives you the out-of-round. Perform the same procedure at the opposite end of the bore. To find the taper, figure the difference between the two in-line measurements and the difference between the two 900 measurements. Now check the largest out-of-round figure and the largest taper figure against the tolerances listed in the TM. If the bearing is not reusable, install new bearings and repeat the procedure. This will complete the repair of the piston assembly, and we can move on to the repair of the cylinder head. Connecting rod bearing running clearance is checked by the same method as the main bearing, using micrometers.