ISSUED REVISED PAGE NO. REVISION MO DAY YEAR MO DAY YEAR 04 15 77 01 06 10 1 of 3 B

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DATE: January 6, 2010 Servi ce Instruction No. 1238B (Supersedes Service Instruction No. 1238A) Engineering Aspects are FAA (DER) Approved
SUBJECT: Assembly and Torque Procedures for V-Band Couplings
MODELS AFFECTED: Lycoming turbocharged engines.

TIME OF COMPLIANCE: When assembli ng V-band couplings to the engine.

V-band couplings are employed by Lycoming on certain ai rframe applications such as the Piper Malibu and Saratoga or by other airframe ma nufacturers at various locations in tu rbocharger exhaust systems. They are used primarily to seal joints in the exhaust syst em without the necessity for heavy bolted flanges. The typical V-band coupling joint c onsists of the coupling, two flanges and a metal gasket.

For V-band couplings employed by Lyco ming, a typical example of their in stallation can be found at the transition assembly and rear exhaust adapter pipe as shown in Figure 1. The proper assembly procedure for the V-band coupling is as follows:

CAUTION Proper installation is critical. T ubes and components to be joined must be aligned with each other before installation of the V-band couplin g. Flanges must also be aligned correctly with zero gap between flange faces prior to V-band coupli ng installation to ensure good joint performance.

1. Slip V-band coupling (1) over th e exhaust adapte r pipe (2).
2. Place the special metal gasket (3) in position with lip of gasket facing exhaust adapter pipe (2).

NOTE 1 Anytime a V-band coupling is disassembled, a new gasket must be inst alled at reassembly. This will ensure maximum sealing efficiency of the joint.

3. Join the machined flange of the transition assembly (4) and the coupling flange of the exhaust adapter pipe (2).
4. With both flanges joined, assemble the V-band c oupling (1) over both flanges and the gasket (3). 

# SERVICE INSTRUCTIONISSUED REVISED PAGE NO. REVISION MO DAY YEAR MO DAY YEAR 04 15 77 01 06 10 2 of 3 B S.I. 1238 5. Press the V-band coupling (1) over the flanges and engage the latch on the coupling. Using a torque indicator wrench, tighten coupling latch nut to a pproximately 70% of torque value. Tap the outer surfaces of the coupling with a rubber mallet to distribute the band tension.

6. Check the torque with wrench, and continue tightening until the specifi ed torque is reached. Repeat as in step 5. until torque reading stabilizes. Do not overtorque.

NOTE 2 Two types of coupling latch nuts may be f ound on 2.00 inch V-band couplings. A split type lock nut, as described with a sp ecified torque of 80 in.-lbs., or a drilled hex. nut secured with safety wire, having a torque value of 75 in.- lbs. See Table 1 for additional information.

TABLE 1 – V-BAND COUP LING TORQUE DATA

Coupling Size Tube OD Lycoming Part No. Vendor Part No. V-Band Coupling

Type T-Bolt Split Type Locknut Torque In.-Lbs. 1/4 Inch Drilled Hex. Nut with

Safety Wire Torque In.-Lbs. 1.00 in. LW-12093-1 MVT69183-100 Spot-Welded 45 -- 1.25 in. LW-12093-2 MVT69183-125 Spot-Welded 45 -- 1.50 in. LW-12093-3 MVT69183-150 Spot-Welded 65 75 1.75 in. LW-12093-4 MVT69183-175 Spot-Welded 65 75 2.00 in. LW-12093-5 MVT69183-200 Spot-Welded 85 75 2.25 in. LW-12093-6 MVT69183-225 Spot-Welded 85 75 2.50 in. LW-12093-7 MVT69183-250 Spot-Welded 85 75 2.75 in. LW-12093-8 * MVT69183-275 Spot-Welded 85 75 1.75 in. LW-12125-1 NH1008723-20 Spot-Welded 65 -- 2.00 in. LW-12125-2 NH1008723-30 Spot-Welded 85 -- 2.25 in. LW-12125-3 NH1008723-10 Spot-Welded 85 -- 2.50 in. LW-12125-4 NH1008723-40 Spot-Welded 85 -- 3.00 in. LW-12125-5 NH1008723-50 Spot-Welded 85 -- 3.69 in. LW-13464 U4204-55-369M Spot-Welded 70 -- 3.69 in. LW-15768 NH1004420-10 Spot-Welded 70 -- 3.30 in. 40D23255-340M NH1009399-10 Riveted 50-60 -- 3.69 in. 40D22382 NM115002-0225 Spot-Welded 80-90 -- 3.15 in. 40D22383 NH1008896-10 Spot-Welded 80-90 -- 3.61 in. 40D23026 NH1009507-10 Spot-Welded 80-90 --

* - TIO-540-AE2A installations: The latest revision of Service Bulletin No. 492 states that P/N LW-12093-8 must be removed at the next periodic inspection. Replace with P/N 40D23255-340M.ISSUED REVISED PAGE NO. REVISION MO DAY YEAR MO DAY YEAR 04 15 77 01 06 10 3 of 3 B S.I. 1238 Figure 1. Illustrative Example of Exhaust Mani fold Gasket and V-Band Coupling Assembly