ENGINE REPAIR

1. Engine Block Inspection and Repair

Figure 5-1 illustrates typical parts of a disassembled engine. Each part must be inspected.

Disassembled engine

In most cases, the parts may be installed as they are repaired. But, since you are primarily concerned at the present with repair, reassembly will be covered in the next study unit. Begin your repair with the engine block. Before repairing the engine block, there is a little more cleaning to be done. You cleaned the external portion of the block during the engine repair preparation phase; now the inside must be

cleaned. Only after this is done can a thorough inspection be made. With a high-pressure steam-cleaning unit or cleaning solvent, clean all water and oil passages and the cylinder walls. If the oil passages are not clear when you reassemble the engine, all the efforts to rebuild or repair the engine will be wasted because you are likely to experience lubrication failure. Now, examine the block thoroughly for cracks. When a crack is present, it is usually indicated by a thin line of rust. These cracks may be found any place on or inside the block. They are most easily detected in machined surfaces such as the gasket surfaces and the cylinder walls. After this has been done, or even while it is being done, check all machined gasket surfaces for nicks, burrs, and scores. Any burrs and scores may be smoothed out with an oil stone, but if the block is cracked, seek the advice of the machine shop personnel. They may be able to seal it; however, if they cannot make the repairs, the block must be replaced.

2. Cylinder Block Inspection and Repair

The cylinder block must also be checked for warpage. If it is warped, the cause may be a leaking or "blown" cylinder head gasket. Lay a straight edge across the top of the cylinder block where the cylinder head gasket is placed. Now, drag the straight edge along the surface of the cylinder block and look for "daylight" between the straight edge and the cylinder block. In those places where you detect a gap between the straight edge and the block, check the clearance with a feeler

gage by inserting the leaves of the gage between the straight edge and the block. Record all your readings and check your results against the tolerances listed in the TM. If the cylinder

head gasket surface is found to be warped, the machine shop personnel will have to grind it flat if tolerances permit. CHECK THE TM FIRST! You just might find that the block you are working on cannot be ground under any circumstances.

Checking cylinder block warpage.

If the block must be ground, make a note of this. DO NOT submit the work to the machine shop until you have found all the defects. There may be more work for machine shop personnel and they might as well complete it all at the time you submit the block for repair. After all defects are located, send the block to the machine shop if necessary and accomplish your repair upon its return.

3. Cylinder Inspection and Repair

Next, check the cylinders (or cylinder liners) for distortion (more commonly called "out-of-round") and cylinder taper. This is done by taking measurements in each cylinder. These

measurements are made with a cylinder bore checking gage, which is a dial indicator. The gage may be moved from the top to the bottom of the cylinder, allowing you to measure the taper at each measuring point (usually two mesasurements at the top and two at the bottom, but check specific TM for engine measuring points) without removing the gage.

Checking cylinder out-of-round and taper.

Record the reading at each measuring point. Determine the amount of out-of-round by subtracting the smaller of the two top measurements from the larger. To determine the amount of cylinder taper, subtract the top readings from the bottom readings. Check your TM specifications to determine whether the taper and out-of-round are within reusable limits. Assume for the moment that the cylinders are not reusable in their present condition. In this case, you must rebore the cylinders and replace the present pistons with oversized pistons. The

machine shop personnel will rebore the cylinders for you. If reboring is not required it will be your job to prepare the cylinders for reassembly. This procedure is known as honing.

You must hone the cylinder walls to remove the mirror smooth finish. This will also remove minor scores and rough areas and aid the new piston rings in seating when they are installed. The hone is placed inside the cylinder and adjusted to a snug fit. Attach a heavy-duty electric drill motor to the hone and apply a small amount of engine oil to the honing stones. Begin drilling, moving the hone up and down inside the cylinder.

Honing the cylinder.

Caution: During the honing process, the honing stones MUST BE KEPT WET; so, continue to squirt oil on the honing stones to prevent them from becoming dry. When you feel that you have eliminated the scores and rough spots, switch the drill off and remove it. Now, wipe the cylinder walls dry and inspect them to ensure that all defects are removed. If defects remain in the cylinder, and it appears that a considerable amount of honing will be necessary to remove them, consult the machine shop personnel. It may be necessary to rebore the cylinder.

4. Cylinder Liner Replacement

If the engine you are working on is equipped with insert-type cylinders (mentioned earlier in the course), the inserts may be replaced rather than bored. If you find that you must replace a cylinder insert (liner), the piston must be replaced also. The piston and liner are issued as a matched set. Replace cylinder liners that do not meet requirements specified in repair and rebuild standards. 

Cylinder liner remover and replacer tools.

When a cylinder liner is installed, it must be positioned over the cylinder bore with the flange end up. Let's continue now with the valve tappet bore.

5. Valve Tappet Bore Inspection and Repair

Now that you have checked and repaired the cylinder bores, proceed with the valve tappet bores if the engine you are working on requires it. The tappet bores are checked visually. Check the bore walls for scoring and burring first. If scores or burrs exist, they must be removed. If the defects are not too deep, you may remove them with crocus cloth. However, if the defects can't be removed with crocus cloth, you must replace the cylinder head or the engine block depending on tappet location.

6. Camshaft Bores Inspection and Repair

Now, check the camshaft bearings. Inspect the bearing surfaces first to determine whether new camshaft bearings are needed. If the bearings show signs of scoring, pitting, or excessive wear, they must be replaced so that the valves will open and close properly for maximum engine performance. Below illustrates the camshaft bearing remover/installer used to remove and replace the old

bearings.

Camshaft bearing remover/installer.

Remove the camshaft bearings: The front and rear (outer) bearings are removed from the front and rear respectively using the driver handle and appropriate adapter. First remove the camshaft bearing plug by knocking it out from within the engine with a wooden dowel or suitable metal bar. With the rear bearing plug removed, you may now install the adapter appropriate to the bearing diameter and the driver handle. Remove the bearing by driving it through the

bearing bore.

Removing outer camshaft bearings.

Remove the inner camshaft bearings by placing the pilot in the outer bearing bore and running the threaded rod through the pilot through the inner bearing. Attach the appropriate adapter to the threaded rod and draw the inner bearing out of its bore by turning the threaded rod. As stated before, the end from which you remove them depends on the length of the engine (it is usually best to remove them from the closest end). BELOW will give you a better idea of how the inner

bearings are removed.

Removing the inner camshaft bearings.

With a piece of chalk or other suitable marking material, mark the location of the oil holes in the engine block. Install the new camshaft bearings: Install the new bearings beginning with the last bearing removed. Place it on an adapter of the remover/replacer which is larger in diameter than the bearing. Now, place the bearing and adapter against the bore in which it is to be installed. Insert the shaft through the adapter, install the adapter nut, and with the appropriate wrench, draw the bearing into the bore until the adapter flange is flush with the bearing bore. Once installed, measure inner bore diameter and inspect the bearing oil holes to ensure that they are aligned with the oil holes of the bearing bore. If not, they must be removed and reinstalled correctly. Remove the expansion plugs: With the installation of the last camshaft bearing, you are ready to take the final step in the repair of the engine block--replacement of the expansion (core) plugs. Defective expansion plugs cannot be detected until they actually begin to leak. Therefore, it is advisable to replace all expansion plugs during the rebuilding of an engine. A sound method of removing a plug is to drill a 1/2-inch hole in the center of the plug and remove it with a slidehammer type puller. You might have noticed that this is the same puller used to remove the clutch pilot bearing from the rear of the crankshaft.

Removing expansion plugs.

Install the expansion plugs: After you have removed the expansion plugs, the new plugs are easily replaced with the expansion plug replacer, illustrated in figure 5-10A. Simply place the expansion plug on the end of the replacer and, placing it against the expansion plug recess, strike the end of the replacer gently until it seats evenly in the recess. Once it has seated, continue striking it until the flange of the replacer is flush with the engine block. With the installation of the last expansion plug, you are ready to set the engine block aside and begin work on the crankshaft.

Replacing expansion plugs.