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250-c20 CSL-1009

COMMERCIAL SERVICE\/ Dy%mit Diesel Allison il Indianapolis. Indiana 46206

LETTER

Pagelof 11January 20, 1972FAA-DER ApprovedSUBJECT: Ear ly Lightoff or AfterfireDuring engine startup or shutdown, some operators have experienced anearly lightoff or afterfire with the twist grip in FUEL OFF and under boostpump pressure. As a result, some eng ines exceeded TOT limits, whichrequires a mandatory inspection or turbine change.To avoid a mandatory engine inspection or turbine change, this CSL revisesthe regular shutdown procedure which w ill be included in the next 250-C.20Operation and Maintenance Manual revision. It also provides maintenanceaction intended to prevent an early lightoff or afterfire caused by (1) the fuelcontro l not in cutoff and/or (2) a worn fuel cutoff valve,.SHUTDOWN:

INSPECTIONSCHEDULE:

EFFECTIVITY:

1. In addition to the regular Flight Manual procedure,monitor your instruments to insure that engineshutdown has actually occurred.CAUTION

TO ASSURE THROTTLE CUTOFF, HOLD TWISTGRIP IN CLOSED POSITION UNTIL THE Nl DE-CELERATE S TO ZERO AND TOT IS STABILIZING.2. Check for TOT decrease, etc.

Component TimeNew fuel controls which Before next days flight;have accumulated 1-25 hr. repeat at 50-hr intervals

until control is repaired.Fue l controls which have Within next 50 flight-hr ;accumulated more than repeat at 50-hr intervals25 hr. until control is repaired.

All fuel control assemblies prior to and includ ingS/N lAAC284 and S/N lAAC328 thsough lAAC359.

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FUEL CONTROL 1. Check fuel control quadrant reading. It must beQUADRANT CHECK: 0 to minus 2 with throttle lever aga inst min. stopwhen the twist grip is in FUEL OFF.2. If the quadrant reading exceeds 0, readjust the minimumstop on the fuel control to 0 to minus 2 on the fuel controlquadrant. The minus 2 position may be obtained by ad-justing the minimum stop screw to O, then out one-halfturn from the 0 position. Check the quadrant to be surethe pointer is at 0 to minus 2 when the twist grip is inFUEL OFF.

FUFLCUTOFF 1. Disconnect ignition lead from igniter (refer toVALVE OPERA- 250-C20 Operation and Maintenance Manual).TIONAL CHECK: CAUTION

Do NOT ENERGIZE IGNITION EXCITER WHILETHE SPARK IGNITER IS DISCONNECTED.2. Disconnect the flexible line from the fuel nozzleand place the free end in a suitable container.3. Turn on the aircraft switches required to providefuel boost pump pressure to the engine.4. Rotate the twist grip toward IDLE, then returnit to FUEL OFF.5. If fuel flows from the flexible line, or exceeds20 drops per min., with the twist grip in FUELOFF, you have a worn cutoff valve requiringrepair.

NOTERepeat this check at least twice before acceptingor repairing the fuel control

6. If the fuel cutoff valve operates satisfactorily, con-nect the fuel line and ignition lead (refer to the250-C20 Operation and Maintenance Manual).


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FUEL CONTROLREPAIR:

PERSONNELREQUIREMENT:

FACILITYREQUIREMENTS:

TOOLREQUIREMENTS:

These instructions apply to Mode l M,C-40 Fuel Controlsserial numbers up to and including lAAC284 and lAAC328through lAAC359 which have not pre,viously been reworkedand identified in accordance with the instructions herein.NOTE

Controls reworked to these instructions are markedwith the letter S stamped in the upper right-handcorner of the nameplate.Do not start repairing fuel controls until the specialtools and replacement parts defined i.n this CSL areavailable from your distributor.The assembly and disassembly o? the fuel controlcovered in these instructions must be accomp lishedby a qualified fuel system technician to insure thatinternal control settings are not disturbed during partremoval and replacement.The rework of the fuel control housing covered in theseinstructions must be accomp lished by a qualified me-chanic or maaist to prevent damage which wouldrequire replacement of the main bousing.The work covered in these instructions must be per-formed in a clean environment to prevent any contami-nation from entering the control.Two special tools or their equivalent are required asfollows:STD 67298 Chamfer Tool, Shut Off Port (Figure 1)Required to incorporate a 0.006-o. 010 inch x 45chamfer on the fuel outlet passage in the main housing.STD 67299 Stick, Chamfer Blending (Figure 2)Required to incorporate a light b lended edge on the chamfer.


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NEW PART REQUIREMENTS:Part No. Nomenclature Qty93393 Cutoff Valve 178109-024 Packing 178109-007 Pat king 178147-008 Packing for shaft assy 1MS24665-151 Cotter Pin 1

PROCEDURE:1. Disassembly

1.1 Remove lockwire from the three screws (30, 31, 32, Figure 3)which secure the cutoff valve cover (29, Figure 4).1.2 Remove nuts (4, 6, Figure 4), washer (7), and cutoff lever (9).

CAUTIONDO NOT LOOSEN POSITIONING NUTS (20, 37, 38, FIGURE 3)ON CONNECTING LEVER (22).

1. 3 Remove cotter pin (18) and spring (19).1. 4 Pos ition control so that cutoff va lve cover (29, Figure 4) isfacing upward.1.5 Remove three screws (30, 31, 32, Figure 3) and washers (33).1.6 Using a suitable tool, push down on cutoff cam and shaftassembly and carefully remove cover (29, Figure 4) withoutmoving or rotating the cam and shaft assembly.

CAUTIONCUTOFF CAM AND SHAFT AS SEMBLY MUST BE LEFT INITS CORRECTLY INSTALLED POSITION AS THE COVERIS REMOVED.

NOTEBefore removing, note installed position of valve (12, Figure 4)to insure correct installat ion at reassem bly.During all subsequent work, the cutoff cam and shaft assem blymust not be rotated.


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250-C20 CSL-1009Pa.ge 9

1. 7 Remove ball (10, Figure 4) and spring (11).1. 8 Carefully remove lockwire and screw (13), (cutoff link (14),and cutoff valve (12).1. 9 Discard cutoff valve (12) and pack ings (2, 3).

NOTE--Only replace packing (15) if damaged to mini.mize the possi-bility of inadvertent rotation of shaft (16).

2. Rework2.1

2.2

2.3

fnspect the edge of the fuel outlet port to insure that it issharp and not already chamfered with the top edge of thechamfer lightly polished and blended.NOTE

The following instructions app ly to fuel outlet ports whichhave sharp edges.If any doubt exists on the cond ition of the edge of the fueloutlet port, tool STD 67296 can be adapted as shown inFigure 1 and used to insure that the proper edge conditionsas defined in this CSL are met.Place tool STD 67298 on the outlet port. Measure the gapbetween the tool bushing and tool stop as sho.wn in Figure 1.This gap should be 0.006-o. 010 inches as measured with afeeler gage. Adjust the tool stop if required to obtain a0.006-o. 010 inch gap.After the proper gap has been obtained, machine a 0.006-0.010 inch chamfer on the outlet port by turning the toolreamer clockwise until the tool stop just cornacts the toolguide.


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250~czcl CSL-1009Page 10

2. 4 Using Chamfer Blending S tick STD 67299, very lightly blendthe edge of the chamfer as shown in Figure 2.CAUTION

BEFORE USING STICK STD 67299, INSURE THAT THE120 BLENDING FACE ON THE END OF THE STICK ISFLAT AND NOT GROOVED FROM PREVIOUS USE. RE-DRESS THE STICK IF REQUIRED SO THAT THE REQUIRE-MENTS SHOWN ON FIGURE 2 WILL BE MET.2. 5 Clean the face of the ho using and the bore of the outlet portwith compressed air.2.6 Treat the reworked edge of the port with Alodine.

3. Assembly3. 1 Install new cutoff valve (12, Figure 4) into cutoff link (14)and secure to shaft assemb ly (16) with screw (13). Torqueto 4 to 6 lb. in. and lockwire using MS20995C20 wire (0.019-0.02 1 inch diameter).3.2 Install new packing (15) on shaft (16) only if old seal isdamaged.3.3 Install spring (11) and ball (10) in end of cutoff valve (12).3.4 Install new packings (2,3) to cover assembly (29) and installcover assemb ly to fuel control. Caution must be taken notto dislocate ba ll (10) or to ratate shaft (16).

NOTEApp ly a light coat of Petrolatum, Federal S pecificationVV-P-236 to all three packings to assist reassembly.

3. 5 Secure cover assembly to the control with three screws(30,31,32, Figure 3) and washers (33). Torque screwsto 26 to 32 lb. in.3.6 Install spring (19, Figure 3) and cotter pin (18). Bendcotter pin.


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Install cutoff lever (9, Figure 4) and secure with nuts (4,6)and one washer (7). Torque nut 4 to 18 to 22 lb. in. andnut 6 to 8 to 12 lb. in.Lockwire three screws using wire MS20995EY20.To compensate the setting of the shutoff valve for the chamferadded to the fuel outlet port, turn nut (37, Figure 3) closestto the throttle shaft 2//3 of one turn (4 flats only) towards thethrottle shaft. Then turn the outboard nut (38) the same amountin the same direction to lock the shutoff valve linkage.After the nuts have been repositioned, lightly stake the threadson the link (22, Figure 3) adjacen t to the nuts to prevent move-ment of each nut.

CAUTIONLINK (22) MUST BE SUPPORTED DURING STAKING O FTHE THREADS.

4. Identification4. 1 Mark controls reworked to these instructions, with an Sstamped in the upper right-hand corner of the namep late.4.2 Record the Seria l Number of the repaired fuel control in the

White Pages, Part HI of the Engine Log Book:.5. Installation

5. 1 Reinstall the repaired fuel control (refer to tlhe 250-C20Operation and Maintenance Manual).5.2 After the control has been repaired, perform the fuel cutoffvalve operational check to insure that fuel shutoff occurs.

d. 0. Davidson, ManagerAerospace ServiceMJK/mjp

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Csl 1009