(i) Autofeatheradjustment
(1.) Location:Insideenginecontrolspedestalon powerlevercables.
(2.) Place a stripof masking orother suitable tapeon upper pedestalcoverbetweenpower
levers. (3.) Startbothengines. (4.) Advance bothpowerleversto 80 to 83 percent Ng. Markpower lever positionon tape. (5.) Shutdown engines. (6.) Set power levers to position marked ontape. (7.) Remove enginecontrolspedestalaccesscovers.
CAUTION: WHENPOSITIONINGMICROSWITCHACTUATINGCYLINDER,CHECK THATSET SCREWS INCYLINDERDO NOT INTERFEREWITHSWITCH ROLLERS.
NOTE:Theautofeathermicroswitchmountingholesareslotted.Fine adjustments canbe madeby changing switchposition.
(8.) Referto Figure 513. Positionactuatingcylinderso it just makescontactwith autofeather switchroller. Tighten setscrews. (9.) Startengines.
(a.) PositionAUTOFEATHERARMswitchto ARM.
NOTE: Toarm autofeather system,bothpowerlevers must be advanced from 80 to 83percent Ng. Bothtorquemetersmust exceed 675foot-poundsand both bleedairpressuresmust exceed 22psig.
(b.) Advanceboth power levers.
(c.) Check that ARM-AUTOFEATHER lightcomesonbetween80and83 percent Ng.
EFFECTIVITY:
040-999
Jan 10/90 76-10-00
PIPERAIRCRAFT
PA-42-720(Advanced Trainer)
MAINTENANCEMANUAL
C. EngineRun Adjustments (continued)
3. EngineRunning Adjustments (continued)
(j) Checkengineaccelerationmatch.
(1.) Run engines. Advancepower levers. Check that both engines accelerate the same. (2.) To adjust:
(a.) Check that engine controls are rigged correctly.
(b.) If rigging is correct, suspect the slow engine.
1 Check fuel control unitgovernor air pressure(Py) bleed tubefor leaks or restrictions. (Figure 1) 2 Check fuel control unit compressor discharge (P3)deliverytube for leaks or restrictions. a Check P3 filter. Replace as required.
(3.) If adjustments abovefail to correctunevenengineacceleration,refer to Pratt& Whitney Maintenance Manual, p/n 3034342.
(k) Powerlever stagger.
(1.) Cause: Uneven demand for fuel between engines. (2.) Adjust length of powerlever control cablewhenstagger is uniform betweentorquesof 300 and 1000 foot-pounds.
NOTE: Beforeadjustingfuel control unit serratedspacer,scribe a lightreferenceacross serratedparts.
NOTE: Refer to Rigging Of Rear Linkage, Fuel Control Unit, And Propeller Control Cam Assembly, this section for detailed serrated spacer adjustments.
(3.) Adjust fuel control unitfuel control armserratedspacer when stagger increasesas power levers move forward. (Figure 509)
°
(a.) Adjust fuelcontrolunit arm 0.6 counterclockwiseon enginecontrolled by most forward power lever.
°
(b.) Adjust fuel controlunitarm 0.6 clockwiseon engine controlledby mostrearward powerlever. (c.) Adjustlengthoffuel control unit interconnect rodto attach in second hole fromendof fuelcontrolunitarm.
(I) Powerleverknobsplit check.
(1.) Start both engines.
(2.) Set propellercontrolleversto maximum propellerrpm(Np)position.
(3.) Increase poweruntil Np is 1900 rpm on both engines.
(4.) Note relativepositionof power lever knobs and any difference in engine torque.
EFFECTIVITY:
040-999 76-10-00Jan 10/90
76-10-00 Jan 10/90
PIPERAIRCRAFT
PA-42-720(Advanced Trainer)
MAINTENANCEMANUAL
C. EngineRun Adjustments (continued)
3. EngineRunningAdjustments(continued)
(I) Powerleverknobsplitcheck (continued)
(5.) If knob splitexceeds1/8 knob width,or engine torquedifferenceexceeds30footpounds:
(a.) Setpowercontrolsto highestpossibletorquebetween1800and2000foot-pounds permittedbyaircrafthandlingdifficulties. (b.) Set propeller controlsto maintain 1900rpm. (c.) Recordpowerleverknobsplit,gasturbinerpm(Ng),propellerrpm(Np),engine torque(Q),andfuelflow(F/F)ofboth engines. (d.) Determinethe average Ng. (e.) Adjustpowertooperatebothenginesat the averageNg.
(6.) If knobsplit remainsmorethan 1/8knob,but torque differenceis 30 foot-pounds or less, checkaccuracyof engine controlsrigging. (7.) If torque differenceexceeds30foot-pounds,but knobsplit is 1/8 knob or less,calibrate torquegauges. Referto 77-10-00.
(8.) If, after makingadjustmentsandcalibrationsabove,knobsplit or torque difference exceeds1/8knobor30 foot-pounds,referto Pratt & WhitneyMaintenanceManual,p/n 3034342.
BetaNut -
ReferenceLine -
SpecialWasher
(AN960-6)
Rod Plate
DomeNut
PistonNut
Blade Link Arms
PropellerDome Area
Figure510
EFFECTIVITY:
040-999
PAGE
3276-10-00
Jan 10/9076-10-00
PIPERAIRCRAFT
PA-42-720(AdvancedTrainer)
MAINTENANCEMANUAL
C. EngineRun Adjustments (continued)
3. Engine Running Adjustments(continued)
Maximum Np Stop
Bolt Adjustment
Air Bleed Line
(Reset Arm)
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