Crosshead & Connecting Rod [Video Lesson]

In a marine two-stroke diesel engine, due to the angularity of connecting rod, the side thrust by the piston is high. The side thrust increases with the increase in cylinder liner wear. Crossheads are used in large two-stroke marine diesel engines to ease this side thrust and reduce liner wear.

 

The crosshead allows concentric piston movement in a cylinder liner. The side thrust is transmitted from crosshead to crosshead guides. Crosshead guides are attached to the frame of the engine. They are subjected to fluctuating load from the transverse components of the connecting rod. The ends of the crosshead are fitted with guide shoes.

 

crosshead connecting rod

 

The centre of the crosshead is designed as a bearing journal, which is accommodated in the crosshead bearing. The bearing surfaces are white metal-lined bearing shells. The piston rod footrests on the crosshead. To match different engine layouts, shims are inserted between the piston rod and the crosshead.

 

The piston rod is fastened to the crosshead by hydraulic studs and nuts. The nuts are tightened by hydraulic tools. A telescopic pipe mounted on top of one of the guide shoes supplies lubricating and cooling oil to the crosshead, crankpin, and piston.

The guide shoe is fitted with a counterweight to balance the weight of the telescopic pipe. The outlet pipe for piston cooling oil is mounted on top of the other guide shoe. The outlet pipe slides within a slotted pipe inside the engine frame.

 

Oil is led through a control device for each cylinder. The control device checks the temperature and flows before the oil is passed onto the lube oil sump tank. The crosshead has bores for distributing the oil supplied through the telescopic pipe. The connecting rod connects the crosshead to the crankshaft. The crankpin bearings are white metal-lined shell bearings.

 

Watch this Video Lesson

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