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©2010 by Lycoming “All Rights Reserved” 

Lycoming Engines, a division of AVCO Corporation, a wholly owned subsidiary of Textron Inc. 

652 Oliver Street 

Williamsport, PA. 17701 U.S.A

Tel. 570-323-6181 

Fax. 570-327-7101 

www.lycoming.com 

DATE: January 6, 2010 Service 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 assembling V-band couplings to the engine. 

V-band couplings are employed by Lycoming on certain airframe applications such as the Piper Malibu 

and Saratoga or by other airframe manufacturers at various locations in turbocharger exhaust systems. They 

are used primarily to seal joints in the exhaust system without the necessity for heavy bolted flanges. The 

typical V-band coupling joint consists of the coupling, two flanges and a metal gasket. 

For V-band couplings employed by Lycoming, a typical example of their installation 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. Tubes and components to be joined must be aligned with each 

other before installation of the V-band coupling. Flanges must also be aligned correctly 

with zero gap between flange faces prior to V-band coupling installation to ensure good 

joint performance. 

1. Slip V-band coupling (1) over the exhaust adapter 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 installed 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 coupling (1) over both flanges and the gasket (3). 

SERVICE 

INSTRUCTION
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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 approximately 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 specified 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 found on 2.00 inch V-band couplings. A split type 

lock nut, as described with a specified 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 COUPLING 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. 
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Figure 1. Illustrative Example of Exhaust Manifold Gasket and V-Band Coupling Assembly