Piston And Piston Pins - Yanmar 4LHA-HTP Operation Manual

Chapter 2 Basic Engine

5. Piston and Piston Pins

5, Piston and Piston Pins
The piston is made of an aluminum alloy with low thermal ex-
pansion.
There is a clearance between the outside diameter of the pis-
ton and the inside diameter of the cylinder. The clearance is
an important factor that has influence on the lubricity be-
tween the piston and cylinder, lubricating oil consumption
and the noise level of the cylinder.
In Yanmar engines, both piston and cylinder have ident-
fication marks to ensure proper clearance between the
piston and cylinder on their respective top surfaces.
In the Yanmar factory, the piston is assembled into a cylinder
block with the same identfication mark.
The following shows the possible combinations of identifica-
tion marks for the piston and cylinder block.
L
O
L
Cylinder Cylinder Cylinder
M
X
block block block
S X
Note 1 : O....available
X....not available
99.925 or less
99.915 or more
99.910 or more
99.905 or more
99.895 or more
Piston pin
^0
Circlip
i r r l i n ^
Piston application
4 L H A - H T E / H T Z E
- H T P / H T Z P
46.5 (1.83)
Intake
Valve Valve
recess recess
Exhaust 40.5 (1.59)
dia. dia.
Identification of piston
s
MS
ML
O X
X
o o X
o
0
X
DT/ST series Mark
HT series
99.932 or less
99.922 or more
99.915 less 99.922 less
ML
99.917 or more
99.917 less
99.910 less
MS
99.912 or more
99.912 less
99.905 less
99.902 or more
mm(in.)
4LHA-DTE/DTZE
-DTP/DTZP
4 L H A - S T E / S T Z E
- S T P / S T Z P
49.0 (1.93)
42.5 (1.67)
4LHA-HTE/HTZE
-HTP/HTZP
4LHA-DTE/DTZE
-DTP/DTZP
5-1 Piston
5-1.1 Piston head 8nd combustion surface
Remove the carbon that has accumulated on the piston head
and combustion surface, taking care not to scratch the piston.
Check the combusion surface for any damage.
5-1.2 Measurement of piston outside diameter/inspection
(1) Replace the piston if the outside of the piston or ring
grooves are worn.
(2) Measure the piston O.D. at the shown below from the
bottom at right angles to the piston pin.
L
S
HT series
Piston dia. Piston dia.
DT/ST series
2-21
,4LHA Seri,
4LHA-STE/STZE
-STP/STZP
mm
W e a r limit
S p e c i f i e d
99.895—99.925
99.79 99.79
9 9 . 9 0 2 - 9 9 . 9 3 2