How to Inspect Piston Rings, Treatment and Causes of Piston Ring Failure In Marine Engines
Proper working of the piston rings is of extreme importance for the efficient operation of a marine engine. Marine engines are designed for high power outputs and bad piston rings can seriously affect the performance of the marine engine.
Reasons for piston ring failure
1) Piston ring and groove clearance is insufficient because of which the ring can jam in the groove leading to blow past and breakage of ring.
2) Cylinder liner has been excessively worn down.
3) Cylinder liner lubrication is not sufficient.
4) Piston ring has worn down excessively.
5) The cylinder liner and piston diametrical clearance has increased.
The exhaust and scavenge ports of the liners are not properly radiused because of which the ring receives a shock when it slides past the port edges.
Treatment of piston rings
1) Copper plating.
2) Ferox coating and phosphating.
3) Piston rings are coated with chromium plating.
4) Plasma coating.
Inspecting piston rings
1) See that the piston ring surfaces have a bright finish.
2) They should not be worn down.
3) The rings should be well oiled.
4) The rings should have sharp edges and not have burns.
5) Check for appearance of vertical strips or sharp burrs.
6) Check if there are a large deposits of thick carbon because of which the rings cannot move freely in the grooves.
7) See for dry black areas on rings and liners.
8) Elastic tension in the rings should be checked.
When should be piston rings replaced?
1) The piston ring should be replaced if it is found stuck in the ring groove.
2) If the wear down on one side is more.
3) The ring axial height is reduced.
4) The rig wear rate is so high that it will be unsafe to continue with it till the next maintenance.
5) The rings should be replaced if the radial thickness of the ring has varied.
6) The chrome plating is worn down.
What is a wear ring?
A wear ring is made of bronze alloy. A wear rings protects the piston skirt from rubbing on to the liner surface. Wear rings are fitted in the grooves of the piston skirt. They are made into two pieces with clearance at the butts. Wear ring maintains the working clearance.
Piston ring material is harder than the material of the cylinder liner as replacement of cylinder liner is more expensive. Top piston ring should be chromium plated which improves anti-friction conditions.