Inspection Process (Part Two)

in Engine Maintenance and Operation

Cylinder Head

Inspect the cylinder head for internal and external cracks. Use a bright light to inspect for cracks, and investigate any suspicious areas with a magnifying glass or microscope. Carbon deposits must be cleaned from the inside of the head, and paint must be removed from the outside for this inspection. Exterior cracks show up on the head fins where they have been damaged by tools or contact with other parts because of careless handling. Cracks near the edge of the fins are not dangerous, if the portion of the fin is removed and contoured properly. Cracks at the base of the fin are a reason for rejecting the cylinder. Cracks may also occur on the rocker box or in the rocker bosses. Interior cracks almost always radiate from the valve seat bosses or the spark plug bushing boss. These cracks are usually caused by improper installation of the seats or bushings. They may extend completely from one boss to the other. Inspect the cylinder walls for rust, pitting, or scores. Mild damage of this sort can be removed when the cylinders are deglazed. With more extensive damage, the cylinder has to be reground or honed. If the damage is too deep to be removed by either of these methods, the cylinder usually will have to be rejected. Most engine manufacturers, or engine overhaul repair stations, have an exchange service on cylinders with damaged barrels.

Piston, Valve Train, and Piston Pin

When applicable, check for flatness of the piston head using a straightedge and thickness gauge. [Figure 10-2] If a depression is found, check for cracks on the inside of the piston. A depression in the top of the piston usually means that detonation has occurred within the cylinder.

Figure 10-2. A method for checking cylinder flange warpage.

Figure 10-2. A method for checking cylinder flange warpage.

Inspect the exterior of the piston for scores and scratches. Scores on the top ring land are not cause for rejection, unless they are excessively deep. Deep scores on the side of the piston are usually a reason for rejection. Examine the piston for cracked skirts, broken ring lands, and scored piston-pin holes. Do not mistake casting marks or laps for a crack. During major overhaul, most pistons are generally replaced, as it requires more labor to clean and inspect the piston than it costs to replace it.

Examine the valve visually for physical damage and damage from burning or corrosion. Do not re-use valves that indicate damage of this nature.

Using a magnifying glass, examine the valve in the stem area and the tip for evidence of cracks, nicks, or other indications of damage. This type of damage seriously weakens the valve, making it susceptible to failure. If superficial nicks and scratches on the valve indicate that it might be cracked, inspect it using a structural inspection method described later. Examine the valve springs for cracks, rust, broken ends, and compression. Cracks can be located by visual inspection or the magnetic particle method.

Inspect the rocker shaft bosses for scoring, cracks, oversize, or out-of-roundness. Scoring is generally caused by the rocker shaft turning in the bosses, which means either the shaft was too loose in the bosses or a rocker arm was too tight on the shaft. Inspect the rocker arm bushing for correct size by sliding the shaft into the bushings to check for proper clearance between the shaft and the bushing. This clearance is also dimensionally checked during the dimensional inspection to confirm the proper clearance. Often, the bushings are scored because of mishandling during disassembly. Check to see that the oil holes line up. At least 50 percent of the hole in the bushing should align with the hole in the rocker arm. On engines that use a bearing rather than a bushing, inspect the bearing to make certain it has not been turning in the rocker arm boss. Also, inspect the bearing to determine its serviceability. Inspect the valve rockers for cracks and worn, pitted, or scored tips. See that all oil passages are free from obstructions.

Inspect all the studs on the cylinder head for looseness, straightness, damaged threads, and proper length. Slightly damaged threads may be chased with the proper die. The length of the stud should be correct within ±1⁄32 (0.03125) inch to allow for proper installation of safety devices.

Crankshaft and Connecting Rods

Carefully inspect all surfaces of the crankshaft for cracks. Check the bearing surfaces for evidence of galling, scoring, or other damage. When a shaft is equipped with oil transfer tubes, check them for tightness.

Visual inspection of connecting rods should be done with the aid of a magnifying glass or bench microscope. A rod that is obviously bent or twisted should be rejected without further inspection. Inspect all surfaces of the connecting rods for cracks, corrosion, pitting, galling, or other damage. Galling is caused by a slight amount of movement between the surfaces of the bearing insert and the connecting rod during periods of high loading, such as that produced during overspeed or excessive manifold pressure operation. The visual evidence produced by galling appears as if particles from one contacting surface had welded to the other. Evidence of any galling is sufficient reason for rejecting the complete rod assembly. Galling is a distortion in the metal and is comparable to corrosion in the manner in which it weakens the metallic structure of the connecting rod.