Evening capital news. (Boise, Idaho) 1901-1927, 1919-04-06
SPRING OvERHAuL|NC
Of THE ENGINE IS A
NECESSARY OPERATION
Valuable Pointers for Garage
Men and for Owners Who
Can Do Some of Their Own
Work.
Continued from Page One.)

Continued from Page One)
down in the cylinder with the same
motion as that described for valve
grinding. Keep this operation up fol
few minutes and withdraw the pis
ton. Wash the cylinder thoroughly
with gasoline and wipe it dry with
soft cloth. Examine it now to see
how nearly it presents a fine, smooth
surface. When sufficient tapping has
been done to restore the perfect con-
dition of the cylinder it is ready to
be measured for diameter. This meas
urement is noted, and when making or
ordering a new piston the new piston
is made about 0.004 inch smaller than
the new bore. About 0,004 inch is the
proper clearance between the piston
and cylinder wall of 4-inch bore.
REBoRlNG CYLINDERS.
There are cases when the scoring of
cylinder is so bad tapping would be
useless, and the cylinder must be re-
bored. In this case the most salts
factory results are obtained by turning
the reboring part of the Job over to
q machine shop specially equipped for
this class of work.
Next in order are the pistons and
rings. Very much the same can be
said of the pistons as has been said
of the cylinders. Their wearing sur
faces should be perfectly smooth, the
same as the cylinder wall, but if their
surface is badly scored or scratched
there is no repair for them. When q
piston is perfect except for small
amount of even wear, for instance,
0.002 or 0.003 inch too small, the
trouble can be remedied by heating
and expanding the old piston. The
heating is done in charcoal and should
be done very slowly and carefully.
After the piston reaches O red heat
permit the charcoal fire to die out
slowly SO the piston is cooled in its
charcoal bed. Pistons can be ex-
banded to as much as O.004 inch in
this manner If the work is done prop
erly.
Piston rings loose their tension aft
err long use and cease to have enough
strength to press against the cylinder
wall all around. AS result oil is per-
mitted to pass by them and enter the
combustion chamber. Besides, COM
preston sometimes is lost because the
gas is permitted to escape past the
rings. Excessive oil coming UP into
the combustion chamber is one OF the
first indications of poorly fitting rings
II plain rings are to be fitted, care
must be taken to fit them properly. |
The gap between the ends should not
be more than 1-64 inch or less than
0.020 inch. In the case of fitting pat
ented rings, the manufacturer has a |
specially machined ring for each type
of engine, and it would be we'll to spe-
city the make and model engine when
ordering. If the engine has been re-
bored the amount of oversize should |
be stated
When the wristpin is inserted di-
dectly into the piston it is generally |
very tight fit, and considerable |
trouble sometimes is experienced in re-
moving it. A piston pin remover is
needed for this job.
When the piston pin is secured by
the connecting rod and moves in
bushings in the piston bosses it is nes-
essary to remove these bushings when
they become worn. 1t is just as i'm
portant that the piston pin fit snugly
in its bearing as 1t is for the connect
ing rod bearing to fit the crankshaft
pin. When any amount of play is evil
dent in the piston the bushings must be
renewed or, in some cases where the
piston pin works in the boss of the
piston with no bushing arrangement.
the piston bosses must be reamed to
admit the insertion of an oversize pis-
ton pin.
CRANkSHAFT.