Marine Engine-Cross head survey: Q & A

As a recently appointed Chief Engineer you are requested to survey the crosshead of a main engine folloing unscheduled repair due to bearing failure.

1. Outline the information you would request prior to the survey
2. Describe the survey procedure you would adopt stating, with reasons, the areas which should receive particularly close attention.
3.State, with reasons,what information you would you would request and the operations require to observe after reassembly of the crosshead.

Answer:1. Information requested prior to survey
* Previous survey report,engine running hours when survey was carried out,Details of recoded clearances,details of any possible marking on pin,bearing condition.
*Recent L.O analysis,any deteriration in the lubrication quality due to contamination by cylinder oil or fuel may give a guide to why the bearing failed.
*Sample of any detritus found in LO filters, plus any records of anything found in the days leading up to the failure.If white metal found it may indicate that the bearing material was failing over a period of time.

2.
Assuming that the crosshead pin and piston rod assembly is resting on the support brackets bolted to the guides and that the conrod is swung down to crankcase door level.
Inspect bearing half in the con rod(the loaded half)for evidence of scoring,squeezing,wiping,cracking of bearing metal.Scoring will indicate hard particles in LO OR DAMAGE to crosshead pin.Squeezing and cracking points toward overloading,whilst wiping will indicate poor lurication and overloading.Some manufacturers have an overlay of a lead/tin alloy on the tin aluminium bearing metal,and state that bearing should be replaced if the overlay has worn away.Other manufacturers have wedges machined in the bearing material and recommend replacement when wedges are reduced to half original width.
If it is cosidered necessary to inspect the top half of the bearing, then the con rod must be reconnected,the engine turned to BDC and the top bearing cover lifted.

3.On reassemly the crosshead pin and the guide shoe clearances should be taken and recorded.Excessive clearances will not allow a LO film to be built up when the rubbing speed is at a maximum.The engine should be turned through several revolutions and the turning motor ammeter observed for any change in load.This ensure that there is no binding between moving parts.The oil pumps should be switched on and the flow through the bearing and guide shoes observed. this will ensured that there is no binding between moving parts