Page 60 - Introduction to Marine Engineering

Diesel engines 47

be supplied from the lubricating oil system, possibly at a higher pressure
produced by booster pumps, e.g. the Sulzer RTA engine. An appropriate
type of lubricating oil must be used for oil-lubricated pistons in order to
avoid carbon deposits on the hotter parts of the system.

MAN B&W
The L70MC is a single-acting, low-speed two-stroke reversible marine
diesel engine manufactured by MAN B&W. It is one of the MC series
introduced in 1982, and has a longer stroke and increased maximum
pressure when compared with the earlier L-GF and L-GB designs.
The bedplate is made of welded longitudinal girders and welded cross
girders with cast-steel bearing supports (Figure 2.29). The frame box is
mounted on the bedplate and may be of cast or welded design. On the
exhaust side of the engine a relief valve and manhole are provided for
each cylinder. On the camshaft side a larger hinged door is provided.
The cylinder frame units which comprise one or more cylinders are of
cast iron and bolted together to form the requisite number of engine
cylinders. Together with the cylinder liners they form the scavenge air
space and the cooling water space. The double bottom in the scavenge
space is water cooled. The stuffing box fitted around the piston rod has
sealing rings to stop the leakage of scavenge air and scraper rings to
prevent oil entering the scavenge space.
On the camshaft side, access covers are provided for inspection and
cleaning of the scavenge space. The cylinder cover is a single piece of
forged steel, and has bored holes for cooling water circulation. It has a
central opening for the exhaust valves and appropriate pockets for the
fuel valves, a relief valve, a starting air valve and the indicator cock. The
exhaust valve housing is fitted into the centre of the cylinder head. It is
opened hydraulkally and closed by air pressure. During operation the
exhaust valve rotates. The bedplate, frame box and cylinder frames are
connected together with staybolts to form the individual units. Each
staybolt is braced to prevent transverse oscillations.
The crankshaft may be solid or semi-built on a cylinder by cylinder
basis. A shaft piece with a thrust collar is incorporated into the
crankshaft and at the after end has a flange for the turning wheel. At the
forward end a flange is fitted for the mounting of a tuning device or
counterweights.
The running gear consists of a piston, a piston rod and crosshead
assembly and a forged steel connecting rod. The crosshead moves in
guide shoes which are fitted on the frame box ends. The camshaft has
several sections, each of which consists of a shaft piece with exhaust
cams, fuel cams and couplings. It is driven by a chain drive from the
crankshaft.