marine auxiliary engine consist of 2 exhaust and 2 intake valves. Adjusting the tappet clearance or intake/ exhaust valve head clearance is a monthly routine job that been carried out on ship. Tappet clearance are taken so that to prevent problems such as unusual wear on the valve bridge guide and the valve guide. The intake and exhaust valves are poppet valves. The intake valves are generally made of heat resistant steel and exhaust valve are made of very heat-resistant and corrosion resistant Nimonic. The valve mechanism can operate 2 intake or exhaust valves at the same time through a T-shaped valve bridge. To operate 2 intake or exhaust valve at same time it is necessary to adjust valve head clearance or tappet clearance.
Tappet clearance or adjusting the valve head clearance can be done as follows:
- Turn the flywheel and move the relevant cylinder to the top dead center of the compression stroke.
- Loosen the locknut 1 and 3.
- Loosen the rocker arm adjusting screw 2.
- Loosen the valve bridge adjusting screw 4.
- Press down the center of the valve bridge. Hold the valve bridge and tighten the adjusting screw 4 and after that tight the lock nut 3 which prevent from moving the adjusting nut 4.
- Put the feeler gauge into the valve bridge clearance A, and gradually tighten the rocker arm adjusting screw 2. Make sure that there is enough space to easily remove the clearance gauge.
- Tighten the locknut 1 and check if the clearance gauge can be removed easily.
Clearance are specific to the type of engine and which will be mentioned in manual. Usually the clearance for intake valve is 0.3mm and for exhaust valve clearance is 0.6mm, both in cold condition.
