Operational Information

The Medium Speed 4 Stroke Trunk Piston Engine

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 shows the frame of an engine with the liners and crankshaft in place.


An alternative method of construction is shown opposite. A separate bedplate is bolted to an entablature which holds the underslung crankshaft.


Shown here is a partial cross section from a one piece medium speed engine frame. The Crankshaft is underslung, and it can be seen in this example that 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.

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