Dimensional Inspection of Reciprocating Engine

The dimensional inspection is used to assure that the engine’s component parts and clearances meet the manufacturer’s specifications. These specs are listed in a table of limits, which lists serviceable limits and the manufacturer’s new part maximum and minimum dimensions. Many measuring tools are used to perform the dimensional inspection of the engine. Some examples of these devices are discussed as the procedure for measuring the engine’s components for dimensional inspection is explained in the following paragraphs.

Cylinder Barrel

Valves and Valve Springs

Crankshaft and Checking Alignment

Repair and Replacement

The engine components that have failed inspection, or are unrepairable, should have been discarded. The component parts that need repair and replacement are now given the attention required. The replacement components (new parts) are organized and laid out for reassembly.

Minor damage to engine parts, such as burrs, nicks, scratches, scoring, or galling, should be removed with a fine oil stone, crocus cloth, or any similar abrasive substance. Following any repairs of this type, the part should be cleaned carefully to be certain that all abrasive has been removed, and then checked with its mating part to assure that the clearances are not excessive. Flanged surfaces that are bent, warped, or nicked can be repaired by lapping to a true surface on a surface plate. Again, the part should be cleaned to be certain that all abrasive has been removed. Defective threads can sometimes be repaired with a suitable die or tap. Small nicks can be satisfactorily removed with Swiss pattern files or small, edged stones. Pipe threads should not be tapped deeper to clean them, because this practice results in an oversized tapped hole. If galling or scratches are removed from a bearing surface of a journal, it should be buffed to a high polished finish.

In general, welding of highly-stressed engine parts can be accomplished only when approved by the manufacturer. However, welding may be accomplished using methods that are approved by the engine manufacturer, and if it can be reasonably expected that the welded repair will not adversely affect the airworthiness of the engine.

Many minor parts not subjected to high stresses may be safely repaired by welding. Mounting lugs, cowl lugs, cylinder fins, rocker box covers, and many parts originally fabricated by welding are in this category. The welded part should be suitably stress-relieved after welding. However, before welding any engine part, consult the manufacturer’s instructions for the engine concerned to see if it is approved for repair by welding.

Parts requiring use of paint for protection or appearance should be repainted according to the engine manufacturer’s recommendations. Aluminum alloy parts should have original, exterior painted surfaces rubbed smooth to provide a proper paint base. See that surfaces to be painted are thoroughly cleaned. Care must be taken to avoid painting mating surfaces. Exterior aluminum parts should be primed first with a thin coat of zinc chromate primer. After the primer is dry, parts should be painted with engine enamel, that should be air dried until hard, or baked for 1⁄2 hour at 82 °C (180 °F). Aluminum parts from which the paint has not been removed may be repainted without the use of a priming coat, provided no bare aluminum is exposed.

Any studs that are bent, broken, damaged, or loose must be replaced. After a stud has been removed, the tapped stud hole should be examined for size and condition of threads. If it is necessary to re-tap the stud hole, it also is necessary to use a suitable oversize stud. Studs that have been broken off flush with the case must be drilled and removed with suitable stud remover. Be careful not to damage any threads. When replacing studs, coat the coarse threads of the stud with an anti-seize compound.