Cummins/Onan — Exhaust Connections
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. Do not terminate the exhaust tailpipe underneath the vehicle or closer than specified to openings into the vehicle or route it such that it is likely to be damaged. Use approved materials and parts only.
- Excessive back pressure can cause loss of performance and 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 sections of tailpipe; slot the overlapping pipe as shown.
- Use automotive-type tailpipe hangers every 2 to 3 feet (610 to 914 mm); attach to steel framework, not combustible material.
- Do not terminate the tailpipe underneath the vehicle; extend it a minimum of 1 inch (25 mm) beyond the perimeter of the vehicle.
- Do not route the tailpipe such that it will interfere with opening the maintenance door, draining engine oil or coolant, or restrict the air inlet.
- Do not route the tailpipe 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 the tailpipe near fuel lines or fuel tanks.
- Do not terminate the tailpipe closer than 6 inches (153 mm) to any opening into the vehicle interior.
- In high-mount applications, route the tailpipe down and underneath the vehicle; it may be routed inside the hot exhaust duct but not through the interior of the vehicle.
- Route the tailpipe so it will not likely be struck when the vehicle is moving; keep it out of the approach and departure angles and above the axle clearance line.
- The exhaust back pressure under full load must not exceed 2 inches (51 mm) water column as measured within 6 inches (153 mm) of the muffler outlet flange.
Tools required
- gasket Amazon
- 5/16-18 bolts Amazon
- U-bolt muffler clamps Amazon
- automotive-type tailpipe hangers Amazon
Tool links are Amazon searches (affiliate links); manufacturer special tools may only be available from a dealer.
Specs & values
- Tailpipe material: 1-3/8 inch ID, 18-gauge aluminized steel tubing
- Tailpipe extension beyond vehicle: minimum 1 inch (25 mm)
- Clearance to combustible material: minimum 3 inches (76 mm) unless insulated
- Clearance to openings into vehicle: minimum 6 inches (153 mm)
- Maximum exhaust back pressure: 2 inches (51 mm) water column
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.