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Marine Diesel Engines (2 - Stroke)

MARINE DIESEL ENGINE STRUCTURE THE BEDPLATE : The Bedplate is the foundation on which the 2 stroke engine is built. It must be rigid enough to support the weight of the rest of the engine, and maintain the crankshaft, which sits in the bearing housings in the transverse girders, in alignment. At the same time it must be flexible enough to hog and sag with the foundation plate to which it is attached and which forms part of the ships structure. If the bedplate was too rigid, then as the hull flexed, the holding down bolts, which secure the engine into the ship would be likely to break, and there would be a danger of the bedplate cracking. Basically the bedplate consists of two longitudinal girders which run the length of the engine. Connecting these longitudinal girders are the transverse girders which are positioned  between each crankshaft throw, and either side of the thrust collar. Built into the transverse girders are the main bearing pockets for the crankshaft to ru
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4 - Stroke Marine Diesel Engine Construction

THE ENGINE FRAME: The engine frame of a modern 4 stroke medium speed diesel can be produced as a single casting or fabricated from cast steel sections and steel plates welded together. With this design, there is no separate bedplate, frame and entablature as with a 2 stroke slow speed engine. The photograph above shows the frame of an engine with the liners and crankshaft in place. An alternative method of construction consists of a separate bedplate, which is bolted to an entablature which holds the underslung crankshaft. When the Crankshaft is underslung, the load on the bearing caps is transferred back to the frame by the use of tie bolts. Note the use of the side tie bolts - which locate the bearing cap, and prevent sideways movement. THE CONNECTING ROD : The connecting rod in a medium speed 4 stroke engine is subject to an inertia whip loading due to the mass of the con rod swinging about the piston pin. (Because of the lower speed of a 2 stroke engine
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Chain Drives in Marine Diesel Engines

Rotation of camshafts in an engine may be by gears or by chain turned by the main crank. The disadvantage of using gears is difficulty in alignment, lubrication and disadvantage to wear from foreign materials as well as their increased cost.The disadvantage of chains is the requirement for tensioning and their finite life. Although for large installations this can be very long. Wear on the chain pins, bushes as well as the chain sprockets can all lead to a slackening off of the chain. This can lead to 'slap' and changing of cam timing.This alters the leads of the fuel p[umps and exhaust valves.. The degree of angular displacement by checked using a manufacturer supplied poker gauge. Chain damage occurs if the chain is too tight or too slack and the result is fatigue cracking of the links. If the tension is too tight, then this adds to the working stress of the chain. Insufficient tension leads to 'slap' with resultant damage to chain and rubbing strips. Vertical
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