Gear Train
A completely enclosed
DESCRIPTION.
the rear end of the engine as shown in
A gear bolted to the
crankshaft flange drives the camshaft
and balance shaft gears, as well as the
blower drive gear through an idler gear
mounted between the crankshaft and
camshaft gears.
The camshaft gear and balance shaft
gear mesh with each other and run at the
same s p e e d a s t h e c r a n k s h a f t g e a r .
Since these two gears must be in time
with each other, and the two as a unit in
time with the crankshaft gear, the letter
"O" is placed on one tooth of one of the
gears with a corresponding mark at the
root of the mating teeth of the other
gear.
F i g u r e 11B-144. Gear Train and
The camshaft and balance shaft gears are
keyed to their respective shafts and held
T i m i n g Marks
securely a g a i n s t t h e s h o u l d e r o n t h e
shaft by a nut. Viewing the engine from
check whether the "R" timing mark on
the gear train end, the right hand gear,
the crankshaft is aligned with the "R" on
has
left
hand
helical
teeth
(see
the idler gear and record this informa-
This
tion for
reassembly
purposes.
engine is set at standard timing.
The idler gear rotates on a double row,
Balance weights, one fastened to the in-
tapered roller bearing mounted on a sta-
This hub is accu-
ner face of each gear (camshaft and bal-
tionary hollow hub.
rately located on the cylinder block end
ance shaft) are important in maintaining
These are in
plate at the left hand side of the engine
perfect engine balance.
as viewed from the gear train end.
addition to the weights cast integral with
the gears.
A blower drive gear is located on the
Gear train noise is usually an indication
blower side to transmit power to the
of excessive gear lash, scoring, pitting
blower, governor, fuel pump and water
Therefore,
or excessive bearing wear.
pump.
when noise develops in a gear train, the
flywheel housing should be removed and
Since the camshaft must be in time with
train
and
its
the crankshaft, identification marks are
the
gear
inspected. A rattling noise usually indi-
located on two teeth of the idler gear
cates e x c e s s i v e g e a r l a s h w h e r e a s a
with corresponding matchmarks stamped
whining noise is a result of too little gear
on the crankshaft gear and the camshaft
lash.
gear as shown in Figure 11B-144.
Excessive wear and scoring may result
However, timing is advanced on certain
from abrasive substances or foreign ma-
e n g i n e s by
aligning
the
"A"
on
the
terial in the oil, introduced in the engine
crankshaft gear with the "R" on the idler
by such means as removal of the valve
gear.
rocker cover without first cleaning away
the dirt.
Before removing or replacing any of the
g e a r s , i t is advisable to line up and make
The backlash between the various mating
a sketch indicating the position of the
gears in the helix steel gear train is from
To -do this, rotate the
timing marks.
0.003" t o 0 . 0 0 8 " w i t h n e w p a r t s a n d
crankshaft until the timing marks are
0.010" with used parts.
Then
aligned o n t h e c a m s h a f t g e a r .
E n g i n e (Less Major Assemblies)