A-FramesA-frames carry the guides and support the entablature (cylinder block). On older engines, A-frames were individually erected on the bedplate directly above the transverse girders. When boxed in with plating, they formed the crankcase. The trend nowadays is to build the frame box as a separate fabricated construction and then after stress relieving and machining the mating surfaces, mount it on the bedplate. This has the advantage of saving weight.

A small amount of jointing compound is used between A-frame and bedplate to ensure oil tight joint. When the frames are aligned on the bed plate, they are secured together by drilling and reaming and using fitted bolts.

Cracks in A-frame can occur, leading to misalignment and excessive wear of running gear. Cracks can start from the welds, sharp changes in section and where strengthening stringers are terminated sharply. Repairs can involve cutting the crack out, grinding and welding. The danger is after repair there may still be a misalignment.

Lowering the A-frame onto the bedplate. A small amount of jointing compound is used ensure an oil tight jointing.

Frames are aligned and fitted to bedplate by drilling, reaming and using fitted bolts.

Cracking in A frames can take place due to misalignment and excess wear of running gear. Cracks can start from welds and sharp changes in section.