AC 43.13-1A 1972 REACH FIGURE 14.3.-Spark plug reach.
b. Reach, The spark plug reach (figure 14.8) is the threaded portion which is inserted into the spark plug bushing of the cylinder. A plug with the proper reach will insure that the electrode end inside the cylinder is in the best position to achieve ignition. Spark plug seizure or improper combustion within the cylinder will probably occur if a plug with the wrong reach is used.
c. Installation Procedures. When installing spark plugs, observe the following procedure:
(1) Visually inspect the plug for cleanliness and condition of the threads, ceramic, and electrodes.
NoTE: Never install a spark plug which has been
(2) Check the plug for the proper gap setting using a round wire feeler gauge as shown in figure 14.4. In the case of used plugs, procedures for cleaning and regapping are usually contained in the various manufacturers' manuals.
CORRECT
INCORRECT FIGURE 14.4.-Method of checking spark plug gap.
Chap 14 Page 275
(3) Check the plug and cylinder bushing to ascertain that only one gasket is used per spark plug. When a thermocouple-type gasket is used, no other gasket is required.
(4) Apply antiseize compound sparingly to the shell threads, but do not allow the compound to contact the electrodes as the material is conductive and will short out the plug. If desired, the use of antiseize compound may be eliminated on engines equipped with stainless steel spark plug bushings or inserts.
(5) Screw the plug into the cylinder head as far as possible by hand. If the plug will not turn easily to within 2 or 3 threads of the gasket, it may be necessary to clean the threads.
NOTE: Cleaning inserts with a tap is not recommended as permanent damage to the insert may result,
(6) Seat the proper socket securely on the spark plug and tighten to the torque limit specified by the engine manufacturer before proceeding to the next plug.
A loose spark plug will not transfer heat properly and, during engine operation, may overheat to the point where the nose ceramic will become a "hot spot" and cause preignition. However, avoid overtightening as damage to the plug and bushing may resuit.
(7) Connect the ignition lead after wiping clean with methylethylketone (MDK), acetone, or similar material. Insert the terminal assembly into the spark plug in a straight line.
(Care should be taken as improper techniques can damage the terminal sleeves.) Screw the connector nut into place until finger tight;
then tighten an additional one-quarter turn while holding the elbow in the proper position.
(8) Perform an engine runup after installing a new set of spark plugs. When the engine has reached normal operating temperatures, check the magnetos and spark plugs in accordance with the manufacturer's instructions.
d. Operational Problems. Whenever problems develop during engine operation which appear to be caused by the ignition system, it is recommended that the spark plugs and ignition harnesses be checked first before working on the magnetos. The following are the most common spark plug malfunctions and are relatively easy to identify:
Far 693
(1) Fouling,
(a) Carbon fouling (figure 14.68) is identified by the dull black, sooty deposits on the electrode end of the plug. Although the primary causes are excessive ground idling and rich idle mixtures, plugs with a cold heat range may also be a contributing factor.
(b) Lead fouling is characterized by hard, dark, cinderlike globules which gradually fill up the electrode cavity and short out the plug.
(See figure 14.5b). The primary cause for this condition is poor fuel vaporization combined with a high tetraethyl-lead content fuel. Plugs with a cold heat range may also contribute to this condition.
(c) Oil fouling is identified by a wet, black carbon deposit over the entire firing end of the plug as shown in figure 14.5c. This condition is fairly common on the lower plugs in horizontally opposed engines, and both plugs in the lower cylinders of radial engines. Oil fouling is normally caused by oil drainage past the piston rings after shutdown. However, when both spark plugs removed from the same cylinder are badly fouled with oil and carbon, some form of engine damage should be suspected, and the cylinder more closely inspected. Mild forms of oil fouling can usually be cleared up by slowly increasing power while running the engine until the deposits are burned off and the misfiring stops.
(2) Fused Electrodes. There are many different types of malfunctions which result in FIGURE 14.5a.-Typical carbon fouled spark plug.
Par 693 AC 43.13-1А 1972 FIGURE 14.5b.- Typical lead fouled spark plug.
FIGURE 14.5c.- Typical oil fouled spark plug.
fused spark plug electrodes; however, most are associated with preignition either as the cause or the effect. For this reason, any time a spark plug is found with the following defects, further investigation of the cylinder and piston should be conducted.
(a) Cracked Nose Ceramics. Occasionally, the ceramic nose core will crack, break away, and remain trapped behind the ground electrode. This piece of insulation material will then build up heat to the point where it will ignite the fuel/air mixture prematurely. The high temperatures and pressures encountered during this condition can cause damage to the cylinder and piston and ultimately lead to fusing and shorting out of the plug.
Chap 14
AC 43.13-1A 1972
(b) Copper Runout. Some erosion oricupping of the exposed center electrode copper core is normal and will gradually decrease with the service life of the plug until it practically ceases. This condition, depicted in figure
14.6a, is not a cause for rejection until the erosion has progressed to a point more than 8/82 inch below the tip of the center electrode.
The high temperatures and pressures associated with preignition can cause the condition shown in figure 14.6b. In this instance, the copper center electrode melted and flowed out, bridged the electrodes, and caused a shorted condition.
(3) Bridged Electrodes, Occasionally, free combustion chamber particles will settle on the electrodes of a spark plug and gradually bridge the electrode gap, resulting in a shorted plug. Small particles may be dislodged by slowly cycling the engine as described for the oil-fouled condition; however, the only remedy for more advanced cases is removal and re- FIGURE 14.6a.-Typical eroded spark plug.
FIGURE 14.6b.-Typical spark plug with copper runout.
Chap 14 Page 277 FIGURE 14.7.-Typical spark plug with bridged electrodes.
placement of the spark plug. This condition is shown in figure 14.7.
(4) Metal Deposits. Whenever metal spray is found on the electrodes of a spark plug, it is an indication that a failure of some part of the engine is in progress. The location of the cylinder in which the spray is found is important in diagnosing the problem, as various types of failures will cause the metal spray to appear differently. For example, if the metal spray is located evenly in every cylinder, the problem will be in the induction system, such as an impeller failure. If the metal spray is only found on the spark plugs in one cylinder, the problem is isolated to that cylinder and will generally be a piston failure. In view of the secondary damage which occurs whenever an engine part fails, any preliminary indication such as metal spray should be thoroughly investigated to establish the cause and correct it.
(5) Floshover. It is important that spark plug terminal contact springs and moisture seals be checked regularly for condition and cleanness to prevent "flashover" in the connector well. Foreign matter or moisture in the terminal connector well can reduce the insulation value of the connector to the point where ignition system voltages at higher power settings may flash over the connector well surface to ground and cause the plug to misfire. If moisture is the cause, hard starting can also result.
The cutaway spark plug shown in figure 14.8 Far 693
FIGURE 14.8.-Spark plug well flashover.
illustrates this malfunction. Any spark plug found with a dirty connector well may have this condition, and should be reconditioned before reuse.
e. Pre-reconditioning Inspection. All spark plugs should be inspected visually prior to reconditioning to eliminate any plug with obvious defects. A partial checklist of common defects includes:
(1) Ceramic chipped or cracked either at the nose core or in the connector well.
(2) Damaged or badly worn electrodes.
(3) Badly nicked, damaged, or corroded threads on shell or shielding barrel.
(4) Shielding barrel dented, bent, or cracked.
(5) Connector seat at the top of the shielding barrel badly nicked or corroded.
694. IGNITION HARNESSES. Aircraft quality ignition harness is usually made of either medium or high temperature wire. The type used will depend upon the manufacturing specification for the particular engine. In addition to the applicable manufacturer's maintenance and repair procedures, the following is a quick-reference checklist for isolating some of the malfunctions inherent to ignition harnesses.
a. Carefully inspect the lead conduit or shielding. A few broken strands will not affect serviceability, but if the insulation in general looks worn, replace the lead.
b. When replacing a lead, if the dressing procedure is not accomplished properly, strands of shielding may be forced through the conductor insulation. If this occurs, a short Par 693 AC 43.13-1A 1972 will exist in the conductor; therefore, it is essential this task be performed properly.
c. The high temperature coating used on some lightweight harnesses is provided for vibration abrasion resistance and moisture protection. Slight flaking or peeling of this coating is not serious, and a harness assembly need not be removed from service because of this condition.
d. Check the spark plug contact springs for breaks, corrosion, or deformation. If possible, check the lead continuity from the distributor block to the contact spring.
e. Check the insulators at the spark plug end of the lead for cracka, breaks, or evidence of old age. Make sure they are clean.
f. Check to see that the leads are positioned as far away from the exhaust manifold as possible and are supported to prevent any whipping action.
g. When lightweight harnesses are used and the conduit enters the spark plug at a severe angle, use clamps as shown in figure 14.9 to prevent overstressing the lead.
695. MAGNETO INSPECTION. Whenever ignition problems develop and it is determined that the magneto is the cause of the difficulty, the following are a few simple inspection procedures which may locate the malfunction quickly.
However, conduct any internal inspection or repair of a magneto in accordance with the manufacturer's maintenance and overhaul manuals.
o. Inspect the distributor block contact springs. If broken or corroded, replace.
b. Inspect the felt oil washer if applicable.
It should be saturated with oil. If it is dry, check for a worn bushing.
c. Inspect the distributor block for cracks or a burned area. The wax coating on the block should not be removed. Do not use any solvents for cleaning.
d. Look for excess oil in the breaker compartment. If oil is present, it may mean a bad oil seal or bushing at the drive end. This condi- Chap 14
AC 43.13-1A 1972 FIGURE 14.9.-Typical method of clamping leads.
tion could require complete overhaul, as too much oil may foul and cause excessive burning of the contact points.
e. Look for frayed insulation on the leads in the breaker compartment of the magneto.
See that all terminals are secure. Be sure that wires are properly positioned.
f. Inspect the capacitor visually for general condition, and check the mounting bracket for cracks or looseness. If possible, check the capacitor for leakage, capacity, and series resistance.
g. Examine the points for excessive wear or burning. Discard points which have deep pits or excessively burned areas. Desired contact surfaces have a dull gray, sandblasted (almost rough) or frosted appearance over the area where electrical contact is made. Figure 14.10 shows how the normal contact point will look when surfaces are separated for inspection.
Minor irregularities or roughness of point surfaces are not harmful (see figure 14.11); neither are small pits or mounds, if not too pronounced. If there is a possibility of the pit becoming deep enough to penetrate the pad (figure 14.12), reject the contact assembly.
Generally, no attempt should be made to dress or stone contact point assemblies; however, if provided, procedures and limits contained in the manufacturer's manuals may be followed.
Chap 14 Page 279
NORMAL POINT IS SMOOTH
ANAY SANDBLASTE HAS DULL GRAY
APPEARANCE FIGURE 14.10.-Normal contact point.
MINOR IRREGULARITIES - SMOOTH ROLLING HILLS
AND DALES WITHOUT ANY DEEP PITS OR HIGH PEAKS. THIS IS A NORMAL CONDITION OF POINT FIGURE 14.11.-Point with minor irregularities.
WELL DEFINED MOUND EXTENDING NOTICEABLY ABOVE SURROUNDING SURFACE. THE MATING
POINT HAS A PIT OR HOLE CORRESPONDING TO THE MOUND SEEN HERE.
FIGURE 14.12.-Point with well-defined mound.
CAUTION When inspecting the contact points for condition, do not open further than absolutely necessary. Excess tension on the spring will weaken it and adversely affect the performance of the magneto.
h. Adjustment of magneto point gap must be correct for proper internal timing of mag- Par 695
neto. (See applicable manufacturer's publications for internal timing procedures.)
I. Check breaker cam to assure cleanness and smoothness. Check cam screw for tightness. If new points have been installed, blot a little oil on the cam. In addition, check contact point aasembly to ascertain that the cam follower is securely fastened.
I. If the impulse coupling ia accessible, inspect for excessive wear on the contact edges of the body and flyweights. In addition, check the flyweights for looseness on the axles.
k. Further examination of the impulse coupling body may disclose cracks caused by exceedingly tight flyweight axle rivets.
I. Check the magneto ventilatora for proper functioning and obstructions. If drilled plugs are used, they should be in the lowest vent hole of the magneto to serve as a drain for condensation and oil.
696. MAGNETO-TO-ENGINE TIMING. While the actual process of timing magnetos to an engine is covered in the engine manufacturer's technical manuals, the following general procedures may be applied:
Par 695 AC 43.12-1A 1972
a. Before installing a new magneto, the correct "p" gap setting specified by the magneto manufacturer should be verifled.
b. When setting or checking the magneto-toengine timing, always turn the crankshaft steadily in the normal direction of rotation to eliminate any error caused by gear backlash.
c. Recheck magneto-to-engine timing after any point gap adjustment, or after replacement of the breaker points.
d. Never advance the magneto timing beyond the engine timing specification recommended by the engine manufacturer.
•. The possibility of a timing error exists if a timing indicator which attaches to the propeller shaft or spinner of geared engines is used. Engine timing specifications are always given in degrees of crankshaft travel, and cannot be applied directly to geared propeller shafts because of the gear ratio. Therefore, the correct position of the propeller shait, if used for timing, must be determined by multiplying the crankshaft timing angle in degrees before top center (BTC) by the propeller gear ratio.
697.-707. RESERVED.
Chap 14
AC 43.13-1A Pae 281 1972 Section 2. FUEL SYSTEMS
708. GENERAL. Maintain, service, and adjust Integrally bonded and cushioned line support aircraft fuel systems and fuel system compo- clamps are preferred to other clamping and nents in accordance with the applicable manu- bonding methods.
facturer's maintenance instructions. Certain e. Support of Line Units. To prevent possible general fuel system maintenance principles are failure, all fittings heavy enough to cause the outlined below. line to sag should be supported by means other than the tubing.
709. FUEL LINES AND FITTINGS. When fuel 8y8- f. Support Clamps.
tem lines are to be replaced or repaired, con- (1) Place support clamps or brackets for sider the following fundamentals in addition to metallic lines as follows:
the applicable airworthiness requirements. Ad- Approximate ditional inspection and repair practices for air- Tube O.D. distance between eupporte craft tubing systems may be found in paragraph 393. 6"-32" 16" 12"
a. Compatibility of Fillings. All fittings are to 22" be compatible with their mating parts. Al- though various types of fittings appear to be 1"-1¼" 1½"-2" 30" 40" interchangeable in many cases they have dif- (2) Locate clamps or brackets as close to ferent thread pitch or minor design differences bends as possible to reduce overhang (see which prevent proper mating and may cause figure 14.18).
the joint to leak or fail.
b. Routing. Make sure that the line does not chafe against control cables, airframe structure, etc., or come in contact with electrical wiring or conduit. Where physical separation of the fuel lines from electrical wiring or conduit is impracticable, locate the fuel line below the wiring and clamp it securely to the airframe structure. In no case may wiring be sup- OVERHANG ported by the fuel line.
c. Alignment. Locate bends accurately so that the tubing is aligned with all support clamps and end fittings and is not drawn, pulled, or otherwise forced into place by them. Never install a straight length of tubing between two rigidly mounted fittings. Always incorporate at least one bend between such fittings to absorb strain caused by vibration and temperature changes.
d. Bonding. Bond metallic fuel lines at each point where they are clamped to the structure. FIGURE 14.18.- Location of clamps at tube bends.
Chap 14 Par 708
710. FUEL TANKS AND CELLS. Welded or riveted fuel tanks that are made of commercially pure aluminum, 3003, 5052, or similar alloys, may be repaired by welding. Tanks made from heat-treatable aluminum alloys are generally assembled by riveting. In case it is necessary to rivet a new piece in a tank, use the same material as used in the tank undergoing repair, and seal the seams with a compound that is insoluble in gasoline. Special sealing compounds are available and should be used in the repair of tanks. Inspect fuel tanks and cells for general condition, security of attachment, and evidence of leakage. Examine fuel tank or cell vent line, fuel line, and sump drain attachment fittings
CAUTION Purge defueled tanks of explosive fuel/air mixtures In accordance with the manufacturers' service instructions. In the absence of such instructions, utilize an inert gas such as CO, as a purgative to assure the total deletion of fuel/air mixtures.
a. Integral Tonks. Examine the interior surfaces and seams for sealant deterioration and corrosion (especially in the sump area). Follow the manufacturer's instructions for repair and cleaning procedures.
b. Internal Metal Tanks. Check the exterior for corrosion and chafing. Dents or other distortion, such as a partially collapsed tank caused by an obstructed fuel tank vent, can adversely affect fuel quantity gauge accuracy and tank capacity. Check the interior surfaces for corrosion. Pay particular attention to the sump area, especially those which are made of cast material. Repairs to the tank may be accomplished in accordance with the practices outlined in Chapter 2 of this handbook.
c. Removal of Flux After Welding. It is especially important, after repair by welding, to completely remove all flux in order to avoid possible corrosion. Promptly upon completion of welding, wash the inaide and outside of the tank with liberal quantities of hot water and then drain. Next, immerse the tank in either a 5 percent nitric or 5 percent sulfuric acid solution. If the tank cannot be immersed, fill the tank with either solution, and wash the outside with the same solution. Permit the acid to re- Par 790 AC 43.13-1A 1972 main in contact with the weld about one hour and then rinse thoroughly with clean water.
Test the efficiency of the cleaning operation by applying some acidified 5 percent silver nitrate solution to a small quantity of the rinse water used last to wash the tank. If a heavy white precipitate is formed, the cleaning is insufficient and the washing should be repeated.
d. Flexible Fuel Cells. Inspect the interior for checking, cracking, porosity, or other signs of deterioration. Make sure the cell retaining fasteners are properly positioned. If repair or further inspection is required, follow the manufacturer's instructions for cell removal, repair, and installation. Do not allow flexible fuel cells to dry out. Preserve them in accordance with the manufacturer's instructions.
711. FUEL TANK CAPS, VENTS, AND OVERFLOW LINES. Inspect the fuel tank caps to determine that they are the correct type and size for the installation.
a. Venfed caps, substituted for unvented caps, may cause loss of fuel or fuel starvation. Similarly, an improperly installed cap that has a special venting arrangement can also cause malfunctions.
b. Unvented caps, substituted for vented caps, will cause fuel starvation and possible collapse of the fuel tank or cell. Malfunctioning of this type occurs when the pressure within the tank decreases as the fuel is withdrawn. Eventually, a point is reached where the fuel will no longer flow, and/or the outside atmospheric pressure collapses the tank. Thus, the effects will occur sooner with a full fuel tank than with one partially filled.
c. Check tank vents and overflow lines thoroughly for condition, obstructions, correct installation, and proper operation of any check valves and ice protection units. Pay particular attention to the location of the tank vents when such information is provided in the manufacturer's service instructions. Inspect for cracked or deteriorated filler opening recess drains, which may allow spilled fuel to accumulate within the wing or fuselage. One method of inspection is to plug the fuel line at the out- Chap 14
AC 43.13-1A 1972 let and observe fuel placed in the filler opening recess. If drainage takes place, investigate condition of the line and purge any excess fuel from the wing.
d. Assure that Aller opening markings are stated according to the applicable airworthinegs requirements and are complete and legible.
712. FUEL CROSSFEED, FIREWALL SHUTOFF, AND TANK SELECTOR VALVES. Inspect these valves for leakage and proper operation as follows:
a. Internal leakage can be checked by placing the appropriate valve in the "off" position, draining the fuel strainer bowl, and observing if fuel continues to flow into it. Check all valves located downstream of boost pumps with the pump(a) operating. Do not operate the pump (8) longer than necessary.
b. External leakage from these units can be a severe fire hazard, especially if the unit is located under the cabin floor or within a similarly confined area. Correct the cause of any fuel stains associated with fuel leakage.
c. Selector Handles. Check the operation of each handle or control to see that it indicates the actual position of the selector valve. Assure that stops and detents have positive action and feel. Worn or missing detents and stops can cause unreliable positioning of the fuel selector
d. Worn Linkage. Inaccurate positioning of fuel selector valves can also be caused by worn mechanical linkage between the selector handle and the valve unit. An improper fuel valve position setting can seriously reduce engine power by restricting the available fuel flow.
Check universal joints, pins, gears, splines, cams, levers, etc., for wear and excessive clearance, which prevent the valve from positioning accurately or from obtaining fully "off" and "on" positions.
e. Assure that required placards are complete and legible. Replace those that are missing or cannot be read easily.
713. FUEL PUMPS. Inspect, repair, and overhaul boost pumps, emergency pumps, auxiliary Chap 14 Pago 283 pumps, and engine-driven pumps in accordance with the appropriate manufacturer's instructions.
714, FUEL FILTERS, STRAINERS, AND DRAINS.
Check each strainer and filter element for contamination. Determine and correct the source of any contaminants found. Heplace throwaway filter elements with the recommended type. Examine fuel strainer bowls to see that they are properly installed according to direction of fuel flow. Check the operation of all drain devices to see that they operate properly and have positive shutoff action.
715. INDICATOR SYSTEMS. Inspect, service, and adjust the fuel indicator systems according to the manufacturer's instructions. Determine that the required placards and instrument markings are complete and legible.
716, TURBINE FUEL SYSTEMS. The use of turbine fuels in aircraft has resulted in two problem areas not normally associated with aviation gasolines: (1) Entrained water (microscopic particles of free water suspended in the fuel) and (2) microbial contaminants.
a. Entrained water will remain suspended in aviation turbine fuels for a considerable length of time. Unless suitable measures are taken, the fine filters used in turbine fuel systems will clog with ice crystals when the temperature of the fuel drops below the freezing temperature of the entrained water. Some fuel systems employ heated fuel filters or fuel heaters to eliminate this problem. Othera rely upon anti-icing fuel additives.
b. Microbial contamination is a relatively recent problem associated with the operation and maintenance of turbine engine fuel systems.
The effecta of these micro-organisms are far reaching. They can cause powerplant failure due to clogging of filters, lines, fuel controls, etc., and the corrosive acids which they produce can lead to structural failure of integra.
tanks. Microbial contamination is generally 88- sociated with fuel containing free water introduced by condensation or other extraneous sources.
Par 911
Page 284 _AC 43.13-7A 1972
c. Maintain turbine engine fuel systems and 717.-727. RESERVED.
use anti-icing and antibacterial additives in accordance with the manufacturer's recommendations.
Par 716 Chap 14
AC 43.13-1A Рабо 385 1972 Section 3. EXHAUST SYSTEMS
728. GENERAL, Any exhaust system failure should be regarded as a severe hazard. Depending upon the location and type of failure, it can result in carbon monoxide (CO) poisoning of crew and passengers, partial or complete engine power loss, or fire. Exhaust system failures generally reach a maximum rate of occurrence at 100 to 200 hours' operating time, and over 50 percent of the failures occur within 400 hours.
729. MUFFLER/HEAT EXCHANGER FAILURES, Approximately one-half of all exhaust system failures are traced to cracks or ruptures in the heat exchanger surfaces used for cabin and carburetor air heat sources. Failures in the heat exchanger's surface (usually the muffler's outer wall) allow exhaust gases to escape directly into the cabin heat system. The failures are, for the most part, attributed to thermal and vibration fatigue cracking in areas of stress concentration; e.g., tailpipe and stack inlet attachment areas (figures 14.14 thru
14.17).
Failures of the spot welds which attach heat transfer pins, as shown in figure 14.15A, can result in exhaust gas leakage. In addition to the carbon monoxide hazard, failure of heat exchanger surfaces can permit exhaust gases to be drawn into the engine induction system and cause engine overheating and power loss.
730. MANIFOLD/STACK FAILURES, Exhaust manifold and stack failures are also usually fatigue-type failures which occur at welded or clamped joints; e.g., stack-to-flange, stack-tomanifold, muffer connections, or crossover pipe connections. Although these failures are primarily a fire hazard, they also present a carbon monoxide problem. Exhaust gases can enter the cabin via defective or inadequate seals at frewall openings, wing strut fittings, doors, and wing root openings. Manifold/stack FIGURE 14.14.-Typical muffler wall fatigue failure at exhaust outlet, (A. Complete mufler assembly with heat shroud removed; B. Detail view of failure.)
failures, which account for approximately 20 percent of all exhaust system failures, reach a maximum rate of occurrence at about 100 hours' operating time. Over 50 percent of the failures occur within 800 hours.
731. INTERNAL MUFFLER FAILURES. Internal failures (baffles, diffusers, etc.) can cause partial or complete engine power loss by restricting Chap 14 Par 728
AC 43.13-1A 1922 FIGURE 14.15.-Typical muffler wall failure. (A. Complete muffler assembly with heat shroud removed; B.
Detall view of failure; C. Cross section of failed muffler.)
FIGURE 14.16 Typical muffler wall fatigue failure. (A.
Complete muffler assembly with heat shroud partially removed; B. Detail view of failure.)
Par 731 Chap 14