### 652Oliver Street

Williamsport, PA 17701 USA. 717/323-6181 

# MANDATORY I 1

DATE: November 26, 1976 Service Bulletin No. 393C (Supersedes Service Bulletin NO. 393B)

Engineering Aspects are FAA(DEER) Approved SUBJECT: MODELSAFFECTED: Exhaust Slip Joint Modification TIGO-541-E series engines with serial numbers 101-62 thru 698-62. Remanufactured engines shipped before September 15, 1976. NOTE Engines that were inspected and modified in accordance with any previous edition of this bulletin NO. 393 require only the cable change as described in step 6. TIME OFCOMPLIANCE: At 

### next 100 hour engine inspection except engines modified in accordance with Service Bulletin No. 378 in which case change is required in next 25hours. Three previous methods have bee" used to prevent separation of the exhaust pipe slip joints at the rear of the left and right exhaust manifolds. Briefly, Service Bulletin No. 368 describes aspring tensioned rod and clamp device while in Service Bulletin No. 378 a U-bolt clamp assembly and slitted adapter pipe was used. Earlier editions of this bulletin provided for asingle then a double cable assembly to replace the spring tensioned rods and U-bolts. Since then, severa1 instances of stretched cables have occurred indicating that the previous l/16 inch single and double cable assemblies used were insufficient to secure the manifold; consequently, this edition provides a larger single cable (l/8 inch) at each location. Proceed with the following instructions insofar as they are applicable to the engine being modified. 3. Reassemble exhaust adapter pipes to transition assembly using new 78083 kets. Check coupling part "umber. MVT69183- ?=,- 83- 200 Avco Lycoming P/N LW-12093-5 is the number of the correct coupling to be used. Inspect the 3 v-band sections of each coupling with adepth micrometer as show" in figure 2. Any dimension obtained under .230 inch renders the coupling unfit for further service.

1. Remove spring tensioned rod and clamps or u-bolt clamps as may be the case. These parts are not reused. 2. Inspect exhaust adapter pipes for cracks around flange fillet and slits. (Pipes with or without slits may be reused.) Pay particular attention to condition of slip joint, noting any damage which may prevent free movement of the joint. I" addition, check the end of the adapter pipe inside the flange mouth; it must be .090 inch below the surface of the flange face. Use ahand grinder if necessary to obtain this clearance. (See figure 1.)
LW-13027orLW-IO798 REAREXHAUSTADAPTER 

### Figure 1. Exhaust Adapter Pipe Showing Areas Requiring Inspection

Pagelof 3Service Bulletin No. 393C

4. Before installing the couplings around the adapter pipes, make sure the entire exhaust assembly is in alignment; that is, mating flanges must match eachother. Support the exhaust system in this position and proceed to install couplings around flange and engage latch. Tighten coupling nut to 50 inch pounds initial torque. Tap outer periphery of coupling with mallet to distribute band tension.
5. Check torque and continue tightening to a final torque of 70/80 inch pounds, tapping coupling until torque reading stabilizes.

NOTE
Donot exceed tightening torque specified forcouplings, or open them far enough to damage thecoupling wrapper. Over torqueing spreads thev- band section of the coupling and impairs its retaining qualities. 

### INSIDEDEPTH OF CLAMPING AREA MUSTNOTBELESS THAN.230IN.
Figure 2. ExhaustManifold Coupling Inspection Requirement

NOTE The exhaust adapter pipes attached to nos. 5 and 6 cylinders, alongwith the segments attached to the transition assembly, are especially subject to cracks in the area ofweldments and attaching flanges. Replace any that indicate suchdefects. 6. Assemble clamps LW-14504 on adapter pipes approximately 2 inches from slip joint and LW-14525 clamps on left and right exhaust pipes. Connect cable assemblies LW15437 to clamps with attaching parts STD2177 bolt, STD-2178 washer and STD-2044 nuts. Note that 4 of these new LW-15437 cable assemblies, which are now 1/8 inch diameter, replace 8 of thepreviously used LW-14572 cable assemblies that were 1/16 inchdiameter. The indicated quantities are for 2engines. Attach these cables, leaving enough slack toprovide 1/4 inch deflection of the cables after assembly. (See figure 3.) Tighten nuts to 60+ 10 inch/lbs.

NOTE The following kit to perform thismodification is supplied throughAvco Lycoming Distributors. Parts must be ordered before February 1, 1977. Allowance for labor and fullpart credit, F. O. B.Williamsport, Pa. will be provided in accordance with the following schedule. Furnish engine serial numbers toyour Avco Lycoming Distributor forordering parts and submission of aWarranty Application. 1. Engines in compliance with Service BulletinNo. 378

. . . .3hours labor 2. Engines in compliance with Service BulletinNo. 368

. . .. 1hour labor
No allowance for labor isprovided forengines that are in compliance with Service Bulletin No. 393 or 393A; however, 4 cable assemblies, LW-15437 will be furnished at no charge directly fromAvco Lycoming Service Department. Include engine serialnumbers with your request forthe cables.

Page 2 of 3Service Bulletin No. 393C


### NOTE:CABLESAREATTACHED OUTSIDE OFTHECLAMP. STD 2177 

### NOTE RIG CABLES (LW-14572) TOPROVIDE 1/4INCHDEFLECTION WHEN MEASURED MIDWAY BETWEEN CLAMPS-BOTH SIDES. CABLES AREASSEMBLED ON THEOUTSIDE SURFACE OFTHECLAMPS AS SHOWN INTHEINSERT.

STD-2044



### LW-14525

Figure 3.Area of Transition Assembly Showing Cable Assembly

PARTS DATA: KitNo. LW-14608 Exhaust Manifold Retainer (for2 engines) consists of: Qty. Part No. Description

4 LW-14504 Clamp, exhaust pipe, 2.10 in.I.D.* 4 LW-14525 Clamp, exhaust pipe, 2.00 in.I.D.* 4 LW-15437 Cable Assy. 8 STD-2177 Bolt, 1/4-20x 15/16 8 STD-2178 Washer 8 STD-2044 Nut, self-locking 4 78083 Gasket, v-band coupling
*

- Insidediameter of clamp ismeasured with .20gap at opening.
NOTE:Revision "C" changes cable assembly and quantity required. 19025, 19025-A, 19434, 19591

- These numbers forAvco Lycoming reference only.

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