MAIN ENGINE EXHAUST VALVE OVERHAUL

1. Common Problems in Main Engine Exhaust Valves

1.1. Common Issues with Exhaust Valves

• High-temperature corrosion of valve and seat
• Reduced valve lift
• Spring failure
• Valve and valve seat erosion
• Bent valve spindle
• Localized burning on valve and seat
• Broken valve rotator vanes
• Carbon or molten salt deposits in exhaust passage
• Poor cooling of valve cage
• Reseating failure causing exhaust leakage
• Valve banging on closure

1.2. Exhaust Valve Knocking Causes

A. Oil System Deficiencies

• Air in the oil or air drawn into the pump suction side
• Low oil supply pressure
• High oil temperature reducing viscosity

B. Air System Deficiencies

• Incorrect spring air pressure
• Faulty air chamber drain valve
• Malfunctioning air chamber safety valve

C. High-Pressure Oil System Leaks

• Incorrect or faulty throttle screw adjustments
• Leaking oil cylinder piston rings
• Leaking cam-side oil cylinder safety valve
• Damaged high-pressure pipe
• Vent valve leakage at the top

2. Step-by-Step Procedure for Main Engine Exhaust Valve Overhaul

1. Place the exhaust valve on a wooden platform.
2. Loosen nuts to remove the safety strap and oil cylinder.
3. Discard O-rings from the air cylinder.
4. Remove flange screws from the top of the air piston.
5. Release air from the air cylinder.
6. Loosen the air piston from the conical locking ring.
7. Lift the valve housing from the spindle and clean the components.
8. Inspect wear and measure critical clearances using micrometers.
9. Check for valve face and seat damage, including burnout and scoring marks.
10. Measure spindle clearances at multiple points, ensuring wear is within acceptable limits.
11. Check the condition of thrust pads, actuators, and sealing surfaces.
12. Test the valve’s closing mechanism using compressed air and ensure no leaks.
13. Reassemble and verify operational integrity before reinstallation.

3. Exhaust Valve Grinding for Marine Engines

1. For large 2-stroke engines, valve grinding should be performed carefully.
2. Inspect valve seats for pitting or corrosion, as severe damage requires replacement.
3. Ensure valve stems are straight.
4. Use manufacturer-recommended grinding tools.
5. Apply grinding paste to valve faces and seats until a continuous belt forms.
6. Ensure the belt is at least 1.5 mm wide and free from scratches.
7. After grinding, clean thoroughly and apply motor oil on the valve stems before reassembly.
8. Avoid repeated grinding without control to prevent thinning of the valve lid, which can compromise the valve’s strength and lead to failure.