Evening star. [volume] (Washington, D.C.) 1854-1972, 1923-01-14
THE OWNER-D RIVER'S
COLUMN
BY l.. G. HErAfPEL

By l.. G. HErMPEL,
Macdonald College, r. O Canada.
What an Overhaul should Do to m
Engine.
Apart from the general cleaning to
which the engine should be treated
during an overhaul, there are two
things which should be uppermost In
the mind OF the man performing the
| Job. They are, first. to give the en-
gine maximum compression-and sec
ondiy. to take UP all play present
in moving parts.
! The man who would do his own
| overhauling should. before pulling
his engine out Of the car, acquaint
| himself with it's condition regarding
the above points. No one knows bet
| ter than the driver OF the car whether
or not the engine is delivering its
full power, whether or not there are
| are any cylinders pumping oil. He
also knows what there Is to be looked
| for In the way of slapping pistoils,
| loose bearings or any other loose
nesses which cause knocks and rat
ties. II he has a mechanical bent
, he will have made up his mind as to
| the approximate location Of all noises
| which may exist In his engine, and
| his plan of action when he gets to
work will be guided largely by this
knowledge OF the machines condition
Compression Life Of Engine.
Poor compression means loss Of
power and is directly or indirectly
responsible for most engine troubles
| Poor compression means that the
pistons. piston rings and valves do
not make a gas tight Joint. By turn
Ing the engine over slowly with the
hand crank the weak cylinders. II
any. can be detected.
| After the cylinder head has been
! removed, the valves should be re-
moved. marked and examined. The
| condition OF the valve seat will be q
guide as to the source Of compression
losses. II the valves OF any weak
| cylinder show a poor contact line at
| the seat. it is likely that grinding
| them VIII improve the compression
considerably.
II. however. a certain weak cylinder
was affiicted with oil pumping. then
the piston and rings must be re.
sarded with suspicion. The engine
! should be turned bottom up on the
working platform. or low bench. the
crank case is now removed and the
piston and cylinder wall can now
be measured up. To do this q thick.
ness gauge Is used. The correct
! clearance between the outside of
piston and the cylinder wall should
sandth OF an iach for each inch OF
piston diameter. Thus, for three
men cylinder the poston should have
a clearance OF .003 inch, or three
one thousandths Of an inch thick
onethousandths of an inch thick
should fit neatly between the piston
and cylinder wall. These measure
ments are always taken at the bot
Y n al
because the upper end OF the piston
Is always smaller than the open end
! or skirt This Is necessary to pro-
vide for expansion Of the head when
| running.
! II when these measurements are
taken the play present is found to be
.OO6 inch, or six-one thousandths of
/ inch or more, IL Is likely that some
| or the loss OF compression Is due to
too small a piston. though We have
clearance than this and still have
/ good compression. These measure
ments viii decide for the repairman
whether or not oversize pistons need
be Installed. II needed. these should
be listed on the order for new parts.
/ The socket wrenches are now put
! into use on the connecting rod bear
| ing bolts and the pistons removed
| from the engine. Care must be taken
to mark the connecting rod bearing
! caps carefully to prevent mixing or
/, reversing OF these parts. The sh'ms.
/ or levers. should be kept separate for
! each side of each bearing. This will
save much future trouble.
Removing Piston Rings.
The condition OF the piston ring IS
i, cannot be ascertained before the pis-
I ton has been removed from the cylin.
| der. They should be examined for
| cylinder 1T. Dark spots on the out
| side OF them indicate a poor fit
They should be compared with a new
| ring. because they may be worn thin,
| in which case new rings need to be
| fitted. II the rings lack spring, they
! should be discarded and new ones
| fitted.
To remove piston rings, several
pieces Of eheet iron one-half by three
1 inches are Of great assistance. The
| ring Is raised out of the groove and
| a piece of sheet metal inserted under
Il. This piece Is slid around the
| piston and others inserted. one on
] each side of the gap. SO as to raise
| the ring clear OF the groove. when IL
may be slid off. Care must be taken
not to spring rings too far or they
! will break.
The cylinder walls and piston sur