Powerplant Inspection: Some tips for 100-hour/annual inspections

Recip Technology

Powerplant Inspection

Some tips for 100-hour/annual inspections

September 2004

The electrical components use power created by the generator or alternator and store it in the battery. The heat generated by the engine combined with the vibration inside the engine compartment makes inspection of these components absolutely critical.

Starter
The attachment of the starter motor to the engine is checked by simply grasping the starter itself and ensuring that it is firmly attached. Each of the four mounting bolts is checked for tightness. The main electrical lead going into the starter is checked for security, electrical arcing, corrosion, and other obvious faults. The starter ring is checked for missing or broken teeth. As this involves turning the prop, be sure the magneto switch is turned off. You should still observe caution in case an errant connection causes the engine to misfire while being turned.

Alternator
Next is the alternator and alternator belt. The belt is checked for proper tension and condition of its contacting surfaces. This can be done with the belt in place simply by rotating the prop to expose sections of the belt at a time between the pulleys. The inner surface should feel soft, pliable, and free of damage. A hardened sheen may be due to friction heat from slippage on the pulleys. Such a belt will no longer grasp well and should be replaced. Belt tension should be checked to allow approximately 1/4 inch of play in each direction. If there is too much or too little play in the belt, then the position of the alternator must be adjusted. To adjust the alternator position, first loosen the retaining bolt and then pull the alternator into the correct position. After checking for correct tension, re-tighten the retaining nut. Be careful not to over-tighten the belt as this could cause damage to the alternator bearings. Be sure that the safety wire is replaced correctly, securing the tension belt to its bracket. The electrical connections on the back of the alternator should be securely attached with no signs of burns or corrosion. The alternator attach points are checked for security and cracking, as is the mounting area on the engine case itself. As the alternator is subject to significant vibrations, cracking in this area is not uncommon. Finally, check the overall security of the mounting by grasping the alternator and ensuring no unwanted movement is observed.

Starter solenoid
The starter solenoid, typically located on the firewall, should also be checked for security and vibration-induced cracking, both in the device itself and around its mounting area. All wire connections to and from the solenoid are also checked for security and electrical burning.

Other electrical components
All other runs of wire in the engine compartment are checked for security, proper support, chafing, or signs of electrical arcing. The tachometer drive system is simply checked for security and any signs of damage.

Fluid leaks
No leak on an aircraft should be ignored. Fuel leaks and hydraulic leaks demand immediate attention. Small oil leaks on the engine, especially on older engines or radial engines, are quite common and should be carefully monitored. Larger oil leaks should be corrected at the source.

The check for fluid leaks begins with inspection of the lower cowl. Telltale staining will immediately tell you what is leaking, how badly, and will give clues to its source. Small amounts of staining are not uncommon, but still should be cleaned and noted so you have a good base for the next inspection.

Fuel leaks
Any size fuel leak demands immediate attention. Carefully check all fuel lines, drain plugs, gascolators, and fittings for any signs of leaking. To verify the source of a fuel leak, switch on the electric boost pump to pressurize the system and with it running re-check all suspected lines and fittings. With the system pressurized by the boost pump, any source of fuel leaks will quickly become evident.

Pressurize the primer system to check its lines and fittings and those in each cylinder. Due to engine vibration, primer system leaks are not uncommon. If a fuel leak is found from a fitting, you can attempt to correct it by re-tightening the fitting or if it appears to be from an accessory such as a pump or a gascolator, replacing the faulty part.

Oil leaks
Signs of small oil leaks are not uncommon. However, the changing flow of air inside the cowl will often make finding the source of the leak difficult to find. Some areas to check include the oil filter (particularly if it has not been tightened properly) oil hose fittings, the valve covers, the dipstick joint into the crankcase, and the seams of the case itself. If a leak appears to be coming from the seams of the case halves, do not try to simply tighten the case bolts. Torquing beyond manufacturer's specs could easily crack the brittle case, causing problems far more severe than a small leak.

Hydraulic fluid leaks
A reddish oily stain indicates hydraulic fluid leaks and most likely a low level in the fluid reservoir. Typically, these systems are covered during the airframe segment of the inspection, but while you're noticing the stain, this would be a good time to check the associated components and then check and top off the fluid reservoir.

This article was based on a portion of the video 100-Hour/Annual Inspection - Powerplant. The video covers all aspects of the powerplant portion of the 100-hour/annual inspection including pre-inspection checks, compression check, oil system, spark plugs, ignition harness, magneto and timing, electrical system, carburetor and induction, cooling system, exhaust system, engine mount and firewall, propellor, and post inspection check. There is also a bonus section on safety wiring included. To learn more or to place an order, visit www.AMTbooks.com.