A -frame

In large crosshead engine these frames are used to support the cylinder block from the bed plate.These are fitted at each transverse girders.

Tie-bolts pass through these A-frames.In some design, a number of frames with the crankcase casing are fabricated together to form a box before attachment to the engine .A-frames or columns which are fabricated from flat Steel plates welded together.These attachment from the mounting for the crosshead guide, main crankcase covers,Piston cooling supply pump,by Piston cooling return drains.

A-frames are elected on the bed plate to the correct alignment. The assembly forms a rigid box like structure to maitain alignment of all the mountings.

The development of long stroke engine and super long stroke engine has resulted in increase lateral forces on the guide.

This is due to relatively short, connecting rods to reduce overall height of the engine which results in increased angle and a higher lateral force component
In order to maintain structural rigidity
Under the condition. Designs is not to use a plate type of a frame arrangement and prefers to use a strucural frame.

Advantage are :-

A)greater structural rigidity.

B) more accurate alignment of the croos head.

C)Force designation structure is more uniform thus lighter strucure.

D) improve oil tightness

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