South Bend news-times. (South Bend, Ind.) 1913-1938, 1919-11-09

years ago were particularly at fault
on this point-do not provide ade-
quate facilities for checking the
valve settings on their engines This
= particularly true OF tractor en-
CINE manufacturers; but even all
the cars OF the present day are not
free from criticism on this score.
True. adjustable tappets are stands.
ard and always have been with the
exception OF one well known make
OF car. but to follow the advice
often given and screw up the tap
pets until they clear the valve
stems by an arbitrary amount-gen-
orally the thickness OF "a visiting
card-does not necessarily result III
the correct timing OF the valves. /
Depends on Cam.
The amount Of clearance to be T
allowed depends on the contour OF
the cam. and the cam which allows
considerable tappet clearance is /
often more Efficient than one which T.
requires the tappet 90 be set close I
TO the valve; this viii be apparent 7
from the diagrams I and 2. Figure
shows the tappet roller very close /
TO the cam circle and i'm the posi- f.
lion where the tappet just touches
the valve stem, the cam sides are
tangent 10 the cam circle. This cam. I.
as can be seen. is narrow across the (
peak. and so gives a very short pc
riod Of full valve opening. Figure
o. however. which shows a cam /
opening and closing the valve at the /
same respective intervals as the /
other, a greater tappet clearance, |
while the difference in the fully I
open period OF the valve or tho .
dwell OF the cam will at once be /
noticed. Should the cam be under I.
cut-that Is. concave faces-this
argument does not hold good; un-
dercut cams. however. are not usual
in passenger car engines. since they
impose additional stresses on the
tappet gear and are somewhat noisy
in action. In any case. however
there Is nothing 20 indicate TO the
mOtorist on what lines his cams are
designed and since cam designs can
vary. with the aims al ideas of the
individual engineer il certainly can
not be correct TO adjust the tappet
clearance on III engines TO the same
clearance.
t.i.. ton Engines.
That this is so is made evident 10y
a consideration of the correct tap
pet adjustment on two of the most
popular aviation engines. both of
which played an important part i'm
the training Of our aviators for the
front-the Curtiss OK and the His
PIANO Suiza 100 horsepower model /
ON the former the correct valve tap
pet clearance 20 obtain exactly the
desired valve setting is .05O" on both
the inlet and the exhaust valves:
On the latter due to the radically
different contours of the cams. the
correct valve timing is obtained
only when the tappet clearance is
nearly nine times as grcat-0S7" on
both inlet and exhaust valves I'll
- well. therefore. Co check up and
see 10 il that the valve action is ex-
4ctly as 10 should Doe. and where no
provision is made Uy the manufac-
lurer 10 facilitate such checking il
viii be well for the owner 10 make
such provision himself for future
use The hiebt way TO proceed is to
obtain from the engine builders
he correct valve setting for their
particular engine and 90 adjust the
.appets until this setting is obtain
"a. The method is fairly easy and
onsists I'm fixing pointer adjacent
he hy-wheel and then marking on
he primary Of the wheel the posi-
ions at which the valves should
,pen and shut This pointer should
be- made Of sheet steel or iron
about 16-EauEc. and can be fixed as
shown in figure 90 the two hold
Town bolts on the rear cylinder
iange or 20 any other convenient
fastening The point is 10 bring il
directly over the fiy-wheel and hold
fast 20 prevent movement and in
accuracies as result OF such move
ment
Find Top Dead Center
II is now necessary 90 find the TOP
lead center positions and taking
he case Of the ordinary four-cylin-
der engine. we VIII remove the
valve cap from cylinder ! and ease
he compression ON the other three
,ylinders by removing the spark
plugs or opening the relief cocks .
Turn the engine over until the eX-
aaust valve on cylinder I is just
shutting when the piston is near the
-op OF its stroke. then locate its
-op dead center by inserting "a piece
T stiff wire. a sCrewdrier or other
ell-tale into the cylinder and rock /
ng the engine hack and forth
When this point has been located
scribe line across the rim OF The
wheel opposite the pointer and cur
he line in with a three-corncre6 f
iie so that it is quite distinct
punching adjacent IL r. G. I. 4. ttop
,enter cylinders / and 40 II let
.er punches are not available this
marking can be quite easily accom-
3lished with a prick punch Now
AXE a strip OF fairly thin white
paper and wrap il around the cir
conference of the wheel cutting IL
% length so that IL ends just meet
IN the marked line and mark the