Honda C72 Shop Manual page 49

The cam sooft is driven by chain through the timing gear reductioned 1/ 2 . As the
cylinder head is mode of light alloy, not only it is light but cooling efficiency is ex-
cellent as heat conductivity is good, and shope of combustion chamber is idea l semi-
spherical one to get efficient combustion of mixture and also to attain larger com-
pression ratio.
As the cylinder is machined with high rate of precision cooling efficiency and lubrication are
favorabl e, accordingly wearing effect is ver y small. Single row W type Needle Bearing
is used at the big end of the connecting rod to get ample loading capacity at the
bearing.
On the other hand single raw Boll Bearings are used on the crankshaft, where W type
middle parts at 2 stations single raw the needle bearing are used to get larger loading
capacity.
As crankshaft has on important function to convert reciprocating motion to rotation,
inertia force due to reciprocating motion of piston and connecting rod should be reduced
. h t t th 01 t'on The crankshaft can rotate smooth
by putting balance w elg t a ge smoo rev u
I .
running as it is balanced by dynamic balance on the balancing machine after complete
maching.
To reduce vibration a t high speed revolution and to get stability at high speed running
the right and left cronk arm angle of Model CB72 , CB77-1 crankshaft is set 180 degree.
IFor M odel C72, C77 type angle is 360 degreel
CD
®
®
®
96
Fig. 2 ·2. Type ·1 crankshaft
CD
Piston
®
Ro lte r bearing
®
Connecting rod
o
R·crankshaft
®
6205 Z speciat ball bearing
®
Com chaim sprock et
CD
l. crank shaft
®
Oil
pump
drive gear
Fig. 2-3. Type·lt crankshaft
,
B. LUbricating system
Construction and Ope ration
For Hondo 250, 300 oil is supplied under pressure by gear pump and wet-sump
system is applied. The oil pump is attached under crankcase by 6 bolts. The oil
pump is shown in Fig. 2-5 and II I is driving gear and 121 driven gear . Power is trans-
mitted by driving gear 131 meshing with crankshaft gear. As for operation of gear
pump, the· driving gear 1 I I rotates to the arrOw direction and the driven gear 121
rotates counterwise, then degree of vacuum inc reases on the right side sucking oi l
from this side to feed the left side .
Therefore each port of the pump should be carefully inspected to avoid engine
burning or other troubles due to mol lubrication. Such troubles after OCCur due to
oil leakage through inadequate gop between gear teeth and pump main body, or
between gear face and pump body Or pump side cover causing drop of degree of
vacuum .
Lubricating oil sumped in the crankcase is sucked by oil pump to pass through the
Fi g. 2 - 4. Lubricating C irculation
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