Doosan DX140LCR, Shop Manual

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SP001671
Page 17
QSB4.5 Engine
General Cleaning Instructions
Definition of Clean
Parts must be free of debris that can contaminate any engine
system. This does not necessarily mean they have to appear as
new.
Sanding gasket surfaces until the factory machining marks are
disturbed adds no value and is often harmful to forming a seal. It
is important to maintain surface finish and flatness tolerances to
form a quality sealing surface. Gaskets are designed to fill small
voids in the specified surface finish.
Sanding gasket surfaces where edge-molded gaskets are used
is most often unnecessary. Edge-molded gaskets are those
metal carriers with sealing material bonded to the edges of the
gasket to seal while the metal portion forms a metal to metal
joint for stability. Any of the small amounts of sealing material
that can stick to the parts are better removed with a blunt-edged
scraper on the spots rather than spending time polishing the
whole surface with an air sander or disk.
For those gaskets that do not have the edge molding, nearly all
have a material that contains release agents to prevent sticking.
Certainly this is not to say that some gaskets are not difficult to
remove because the gasket has been in place a long time, has
been overheated or the purpose of the release agent has been
defeated by the application of some sealant. The object however
is just to remove the gasket without damaging the surfaces of
the mating parts without contaminating the engine (don't let the
little bits fall where they cannot be removed).
Bead blasting piston crowns until the dark stain is removed is
unnecessary. All that is required is to remove the carbon
build-up above the top ring and in the ring grooves. There is
more information on bead blasting and piston cleaning later in
this document.
Cummins Inc. does not recommend sanding or grinding the
carbon ring at the top of cylinder liners until clean metal is visible.
The liner will be ruined and any signs of a problem at the top ring
reversal point (like a dust-out) will be destroyed. It is necessary to
remove the carbon ring to provide for easier removal of the piston
assembly. A medium bristle, high quality, steel wire wheel that is
rated above the rpm of the power tool being used will be just as
quick and there will be less damage. Yes, one must look carefully
for broken wires after the piston is removed but the wires are more
visible and can be attracted by a magnet.
Oil on parts that have been removed from the engine will attract
dirt in the air. The dirt will adhere to the oil. If possible, leave the
old oil on the part until it is ready to be cleaned, inspected and
installed, and then clean it off along with any attracted dirt. If the
part is cleaned then left exposed it can have to be cleaned again
before installation. Make sure parts are lubricated with clean oil
before installation.
They do not need to be oiled all over but do need oil between
moving parts (or a good lube system priming process conducted
before cranking the engine).
Bead blasting parts to remove exterior paint is also usually
unnecessary. The part will most likely be painted again so all
that needs happen is remove any loose paint.