Exhaust valve

.exh valve

Material for exhaust valve:

The valve housing is of cast iron and arranged for water cooling. The housing is provided with a bottom piece of steel. The spindle or valve stem is made of heat resistant steel with stellite welded on to the seat.

Stellite is a range of cobalt-chromium alloys designed for wear resistance. The alloys may also contain tungsten or molybdenum and a small, but important, amount of carbon.

Cause of Exhaust Valve Burning : Exh vv burning

.exhaust valve burning

.exh v/v burning .exh vv burning  .exhv

CAUSES:

1. Continuous overloading of Engine or particular unit. 
2. Poor combustion (or after burning) of fuel due to dirty fuel injectors, incorrect fuel injection pressure, incorrect fuel temperature, late fuel injection timing, Air starvation, water, or impurities in fuel. 
3. Cold Corrosion (Cooling water temp low) & Hot Corrosion (due to bad quality of fuel),  
4. Incorrect fuel valve spray angle 
5. Insufficient cooling water supply may cause valve to overheat. 
6. Valve not close properly due to Incorrect Tappet Clearance. 
7. Ineffective seal between valve & valve seat. (v/v leakage)
8. Carbon buildup in the valve seat. 
9. Unsuitable materials used. 
10. Valve spindle not rotating. 
11. Running a dry fuel such as L.P.G resulting in inadequate lubrication of the valve seat. 

Indication of Exhaust valve Leaking: 

1. Low Pcom and Low Pmax 
2. High Exhaust temperature 
3. Scavenge Air or Supercharging air pressure will decrease
4.  Noise. 
5. Smoky Operation. 
6. Abnormal light spring diagram showing pressure dropping down. 

Exhaust valve maintenance and clearance checking

1. Use template and filler gauge to measure the wear down the valve seat
2. Use template and filler gauge to measure the bottom piece wear. If wear is beyond the highest limit then replace the bottom piece
3. Replace all the o ring for bottom piece
4. Grind the outer seat of the bottom piece with carborundum and special grinding tool
5. Use vernier calliper to measure the thickness of the spindle and calculate the wear down.
6. Inspect and measure the wear down of the guide bushing at top and bottom by using dial gauge. If wear is beyond the highest limit, then replace the guide bushing
7. Replace all the o ring in the guide bushing
8. Pressure test the air cylinder relief valve
9. Air cylinder piston o ring and Teflon ring replace if necessary
10. Measure the wear down of the oil cylinder piston ring.
11. Measure the wear down of the oil cylinder liner
12. Replace the o ring inside oil cylinder