Yanmar 4LHA-HTP User Manual

Chapter 2 Basic Engine
5. Piston and Piston Pins
,4LHA Seri,
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.
Identification of piston
L
ML
MS
s
Cylinder
block
L
O O
X
X
Cylinder
block
M
X
o o
X
Cylinder
block
S
X
X
0 o
Note 1 : O....available
X....not available
HT series
DT/ST series
Mark
99.925 or less
99.915 or more
99.932 or less
99.922 or more
L
99.915 less
99.910 or more
99.922 less
99.917 or more
ML
99.910 less
99.905 or more
99.917 less
99.912 or more
MS
99.905 less
99.895 or more
99.912 less
99.902 or more
S
Piston pin
^0
irrlin^
Circlip
Piston application
mm(in.)
4LHA-HTE/HTZE
-HTP/HTZP
4LHA-DTE/DTZE
-DTP/DTZP
4LHA-STE/STZE
-STP/STZP
Valve
recess
dia.
Intake
46.5 (1.83)
49.0 (1.93)
Valve
recess
dia.
Exhaust
40.5 (1.59)
42.5 (1.67)
4LHA-HTE/HTZE
-HTP/HTZP
4LHA-DTE/DTZE
-DTP/DTZP
4LHA-STE/STZE
-STP/STZP
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.
mm
Specified
Wear limit
Piston dia.
HT series
99.895—99.925
99.79
Piston dia.
DT/ST series
99.902-99.932
99.79
2-21

Yanmar 4LHA-HTP Specifications

General

Brand	Yanmar
Model	4LHA-HTP
Category	Engine
Language	English