Marine diesel engine troubleshooting guide - Piston failure and engine knocking

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Despite the best of maintenance and care, faults and piston failure can occur in the engine room and in marine diesel engines. One of the main requirements of the job profile of a marine engineer at any rank is to act quickly and thoughtfully to handle any kind of situation. It is important for a marine engineer to know what to do when he hears diesel engine knocking. This diesel engine troubleshooting guide will show you what to do when a piston gets overheated.

Causes of Overheating

A piston is constantly in contact with the high temperature and high pressure region of the combustion chamber while it is performing its functions of pressure sealing and motion transmission to the crankshaft. It can get overheated due to any or several of the following reasons

  • The obvious reason could be the failure of the piston cooling system to perform its function which leads to temperature rise
  • If the piston rings have insufficient clearance or are broken down and get seized, this also will lead to heating of the piston
  • If the cylinder jacket liner lubrication system fails, this would result in increase of heat due to friction
  • Leakage of combustion gases past the piston due to ring fault or failure
  • Bad combustion which could be due to valve timing problems and so forth

External Symptoms

Hence we see that there can be a number of reasons for piston overheating, but remember when this situation occurs you cannot peep inside to find out immediately. First you need to know the external indicators of an overheated piston and they are as follows.

  • Engine RPM falls without any reasonable cause
  • Knocking is heard from the cylinders
  • Abnormal rise in piston cooling temperature
  • Abnormal rise in exhaust temperature
  • Abnormal smoke in exhaust form the funnel

Handling the Situation

So what should be your first reaction if you see or sense an overheated piston? Well the first instinct would be to run and shut down the engine but just take care to avoid this reflex action and this could lead to other problems.

  • Slow down the engine to a very low speed but NOT complete shutdown. This results in considerable reduction of heat in the relevant piston.
  • Since not all pistons would likely develop this fault simultaneously (unless you are totally out of luck that day) so first identify the particular cylinder in which the problem has occurred using parameters such as temperatures, sound etc.
  • The fuel supply to the affected cylinder should be cut-down from the fuel pump
  • Lubrication to that cylinder should be increased from the appropriate arrangement depending on the specific engine under consideration
  • Only stop the engine when it is sufficiently cooled to avoid any thermal stresses. Even after stopping the turning gear should be used to keep it moving for some time while cooling and lubrication is continued.
  • Finally the piston needs to be dismantled and checked and this is a detailed procedure which we might take up in future.

In the next article we will learn about replacing the piston in case such a need arises on board the ship.