Cummins/Onan — Connecting and Routing the Tailpipe
Installation · Exhaust system
From a Cummins/Onan service manual — check it applies to your exact model before use.
Applies to: Cummins/Onan HDKA, Cummins/Onan HDKAJ, Cummins/Onan HDKAK
Before you start
- EXHAUST GAS IS DEADLY! Keep exhaust gases from entering the vehicle.
- Interconnecting engine exhaust systems will allow exhaust condensates and soot to migrate into the idle engine, causing engine damage.
Procedure
- Do not connect the genset to the vehicle engine exhaust system.
- Use 1-3/8 inch ID, 18-gauge aluminized steel tubing or equivalent for the tailpipe. Do not use flexible pipe.
- Secure the tailpipe or adapter flange to the muffler flange with a gasket and two 5/16-18 bolts.
- Use U-bolt muffler clamps to connect tailpipe sections. Slot overlapping pipe as shown.
- Use automotive-type tailpipe hangers every 2 to 3 feet (610 to 914 mm). Attach to steel framework.
- Do not terminate tailpipe underneath the vehicle. Extend minimum 1 inch (25 mm) beyond vehicle perimeter.
- Support tailpipe end so it cannot be pushed inward and up under the vehicle skirt.
- Do not route tailpipe to interfere with maintenance door, oil/coolant drain, or air inlet.
- Do not route closer than 3 inches (76 mm) to combustible material unless insulated or shielded. Temperature rise on adjacent combustible material must not exceed 117°F (65°C).
- Do not route tail pipe near fuel lines or fuel tanks.
- Do not terminate tailpipe closer than 6 inches (153 mm) to any opening into the vehicle interior.
- For high-mount HDKAT, route tailpipe down and underneath vehicle, terminating at least 1 inch (25.4 mm) beyond perimeter.
- Route tailpipe to avoid being struck. Keep out of approach and departure angles and above axle clearance line.
- Exhaust back pressure under full load must not exceed 2 inches (51 mm) water column within 6 inches (153 mm) of muffler outlet flange.
Specs & values
- Exhaust back pressure under full load: max 2 inches (51 mm) water column
- Combustible material temperature rise: max 117°F (65°C)
Full service-parts list: Cummins/Onan HDKA →, Cummins/Onan HDKAJ →, Cummins/Onan HDKAK →
Source: Cummins/Onan service manual. Steps and values are as documented; always cross-check against the official manual and any later revisions for your exact serial number before servicing.