There
is a condition that contributes to many failures of rebuilt
or re-rung engines generally referred to as "fuel wash".
It is caused by engine flooding at initial startup or in early
operation of a newly rebuilt engine.
This
phenomenon can cause very serious damage to the cylinder bores,
pistons, and piston rings. When flooding occurs, either from
a fuel system malfunction, or overfueling when the engine
fails to start, the excess fuel washes the oil film from the
rings and cylinder walls. At this point metal to metal contact
occurs and scuffing takes place. This condition is similar
to and also sometimes referred to as dry start.
It is highly advisable for rebuilders
and installers to follow a program of fuel system maintenance
and ignition system installation checks to greatly reduce
the chance of fuel wash. A suggested program is outlined below.
A carburetor rebuild is recommended
at the time of engine rebuild. If not rebuilt, the carburetor
should be encased in a plastic bag during engine overhaul.
Before installing the carburetor, remove the fuel filter and
direct a soft stream of air into the fuel inlet to ensure
that no dirt or metal particles are in the needle and seat.
Reinstall new fuel filters throughout the system. Blow off
the fitting on the fuel line and carburetor, start the fitting
straight by hand as cross threading will remove metal particles
which can hold the needle and seat open and cause flooding.
Timing
chain, distributor, and ignition system installation should
be done in accordance with the engine manufacturer's manual.
The engine lubrication system should be prelubed with a pressure
tank.
An overhauled engine
that has been correctly assembled will start almost immediately.
If after a reasonable period of cranking the engine does not
start, something is wrong!! At this point the compression,
ignition, and fuel systems should be checked. If, for example,
there is no spark, the fuel being drawn into the cylinders
will reach a saturation point and wash the oil film, or severely
dilute and thus weaken the film, and scuffing will occur.
Although diesel fuel has increased
lubricity over gasoline, fuel wash still must be avoided or
serious damage will result. Engine manufacturers' manuals
should be consulted and closely followed with respect to correct
fuel timing, fuel/air ratios, servicing of injectors, pumps,
etc. Fuel filters and water removal systems should be fully
serviced at overhaul.
In general, the combination of accepted
shop practices cleanliness, good fuel system maintenance,
and good common sense can all but eliminate this potentially
serious problem.
