ENGINE DISASSEMBLY

The disassembly of the engine is as important, if not more so, than the assembly. Many engines have been repaired or rebuilt and returned to operation, but a short time later, are back in the maintenance facility. The greatest cause of this is improper disassembly. Most mechanics concentrate all their efforts on repair of the components known to be defective, but if they also carefully inspect each and every part during engine disassembly, they can replace a defective component at that time, instead of waiting until reassembly to find and replace the component. Proper disassembly requires complete organisation. Components that are paired, such as

valves and tappets, develop wear patterns inherent to each other and must remain paired. This is also true for pistons and connecting rods, tappets and camshaft lobes, bearings and journals, and pistons and their original cylinder, just to name a few. As the engine is disassembled, the parts removed need to be laid out in the order they were removed. This prevents replacing pistons in the wrong cylinder, tappets in the wrong bore, bearings on the wrong journal, etc. As you can see, an entire study unit is devoted to the disassembly phase. You will soon realize that proper disassembly is just as important as repair or reassembly 

REMOVING THE CYLINDER HEAD

- List the four procedures in preparing an engine for disassembly.

-  Identify the differences in removing the cylinder heads from the L-head engine and the I-head or F-head engine.

-  Identify the disassembly procedure for the rocker arm.

The first engine component removed is the cylinder head assembly, but before any disassembly is started, you must prepare the engine. A good repair or rebuild job begins with engine preparation. Without good preparation, you may not only fail to locate unknown defects, but you may also cause further damage.

1. Engine Preparation

With the engine removed from the vehicle, you can begin your preparation. The first procedure is to cover all openings of the engine with clean, lint free rags. Look at the figure below. Note the arrows indicating typical openings to be covered. Now imagine yourself as a surgeon and the engine as your patient. If foreign matter enters your patient's body, infection may result, and your operation could be a failure.

Engine preparation

2. Engine Cleaning

Now that all openings are covered, the second procedure is to clean the engine thoroughly to prevent foreign matter from entering the engine and causing internal damage during disassembly. First, take a high-pressure cleaning unit and steam clean the entire outer surface of the engine. If a cleaning unit is not available, use a high-pressure water hose to remove the dirt and loose matter. Next, with cleaning solvent and a stiff brush, remove any grease or oil that may be on the engine. The third procedure is to drain the engine. Using two separate containers, one for oil and the other for the coolant, remove the oil pan drain plug and open the cylinder block drain cock and drain the engine completely. While the engine is draining, you might use this time to make sure that your working area is thoroughly clean to prevent any chance of getting the internal parts of the engine contaminated with dirt.

Drain the engine

With the engine thoroughly cleaned and drained, the fourth procedure is to conduct a good visual inspection of its outer surfaces for cracks and broken parts as you begin removing the accessories. If these conditions exist, you must get a decision from a machinist on the feasibility of repairing the defects. New or rebuilt parts are of no value if the engine block is damaged beyond repair. At this point, you are ready to disassemble the engine. Mount the engine on the repair stand and begin the actual disassembly. Remember to lay the parts out in an orderly manner as you disassemble the engine. Doing so will make assembly easier. Note: The removal and installation of the intake and exhaust manifolds are not covered in this course. It is essential, however, that these components be inspected and properly aligned for the engine to operate correctly. As you disassemble the engine, check each part to make sure it can be used in the repair of the engine. If you wait until reassembly, it will cause extra work and unnecessary time if you have to remove a part you earlier assumed was good without checking. The three most common cylinder head engine types will be taught. Let's begin with the L-head engine.

3. L-head Engine

You have already inspected the outer surfaces of the cylinder head along with the rest of the engine. The internal portion of the head must be cleaned before it can be inspected. When you remove the cylinder head, lay it aside and inspect it later in a separate area. To clean it now would result in carbon deposits flying through the air, possibly contaminating the rest of the engine. The removal of the cylinder head from an L-head engine is very simple. Remove the cylinder head bolts from the head, lift the cylinder head from the engine, and lay it flat on a flat surface. To stand it on end or lean it against another object would result in the head warping which in many cases could require repairs that would not have been necessary. At this time, also remove the cylinder head gasket, inspect it for signs of leakage, and discard it. Any signs of leakage should be recorded so that you may concentrate on the cause during your cylinder head and cylinder block gasket surface inspection.

4. I- or F-head Engine

Removing an I- or F-head engine's cylinder head requires a little more effort. First, remove the rocker arm cover and discard the gasket and retaining seals. At this time, check the retainer seal surface of the cover for dents. Check for any other dents. Some mechanics have a tendency to over-torque the retaining nuts and bolts; this bends the retainer seal surface of the cover. If a dent exists, you may straighten it at this time or record the defect so that it is not forgotten.

With the cover removed, back off (loosen) the valve adjustment at least one complete turn to relieve the pressure on the rocker arms. If the pressure is not relieved, damage to the rocker arm shaft could result when it is being removed.

Relieving rocker arm pressure

When the pressure is relieved, remove the rocker arm attaching bolts and nuts and lift the rocker arm shaft from the engine. If the engine does not have a rocker arm shaft, simply remove the rocker arm. Once the shaft is removed, you might make a preliminary inspection by removing a couple of rocker arms and checking their pivot points on the shaft. If you find grooves worn into the shaft, discard both the shaft and the rocker arms, retaining all other parts. To prevent damage to the pushrods when the cylinder head is removed, take them out of their holes (before removing the cylinder head) and lay them in order on your workbench or in the area you are storing the parts you have removed. You might as well take this opportunity to ensure that all the pushrods are perfectly straight. A bent rod will continue to bend when reinstalled in the engine. Discard any bent rods and make a note of the holes from which they were removed.

Now, loosen the cylinder head bolts, lift the head from the engine, and lay it on a flat surface.