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78/83/90 Series Horizontal Shaft Engines
66
Lubrication system
MTD uses a splash lube system for its horizontal shaft
engines. The connecting rod has a dipper on it that
“splashes” oil around the inside of the engine.
See Figure 5.5.
NOTE: The cam and the balance shaft were
removed for a better view of the lubrication
system.
The splashing action will create an oil mist that
reaches the cylinder head. There are two oil passages that
run along the engine cylinder. The one on the top side of
the engine is the oil supply passage. The oil mist will flow
through this passage to the cylinder head.
See Figure 5.6.
The second oil passage runs along the bottom side of
the cylinder. This is the oil return passage. As the name
implies, it allows the oil collecting in the cylinder head to
return to the sump. The return passage is the tiny hole that
is in between the two tappet passages.
NOTE: Because these engines use splash lubrica-
tion, the type of oil and the oil level is critical
for proper operation of the engine. If the oil
level is too low, the dipper on the connecting
rod cannot splash the oil into the engine. If
the oil level is too high, the oil will not change
into a mist to reach the upper side of the engine.
Figure 5.5
Dipper
Figure 5.6
Oil supply passage
Oil return
Tappet
passages
For Parts Call 606-678-9623 or 606-561-4983
www.mymowerparts.com