Yanmar 4JH4E - Piston

5. Inspection and servicing of basic engine parts
195
5.3.1 Piston
(1) Piston head and combustion surface
Remove the carbon that has accumulated on
the piston head and combustion surface,
taking care not to scratch the piston. Check
the combustion surface for any damage.
(2) Measurement of piston outside diameter/
inspection
1) Replace the piston if the outsides of the
piston or ring grooves are worn.
2) Measure the outside diameter in the position
of 22mm from the piston bottom in the
direction vertical to the piston pin.
If the piston outside diameter exceeds the limit,
replace the piston with new one.
Selective pairing of cylinder and piston
Piston must be paired with cylinder according to
the below table. The size mark of a piston is shown
on the top surface of the piston and the size mark
of a cylinder block is shown on the non-operating
side of the cylinder block. The service parts of
pistons are provided.
(3) Removing the piston pin
A floating type piston pin is used in this
engine. The piston pin can be pressed into the
piston pin hole at room temperature (Coat with
oil to make it slide easily).
Piston outside diameter
Model Standard Limit
Clearance between
piston and cylinder
3JH4E 87.950-87.960 87.900 0.045-0.075
4JH4E 87.935-87.945 87.885 0.060-0.090
4JH4-TE
4JH4-HTE
83.930-83.940 83.880 0.065-0.095
Piston outside diameter.
D2 = 87.955 mm
Tol er an ce
below + 0.005
0 min.
below 0
-0.005 min.
Size mark ML MS
Cylinder inside
diameter
D1 = 88.000 mm
+0.030 max.
+0.020 min.
L { X
below +0.020
+0.010 min.
M {{
below +0.010
0 min.
SX{
Model
Cylinder inside diameter
D1 (mm)
Piston outside diameter.
D2 (mm)
3JH4E
88
87.955
4JH4E 87.940
4JH4-TE
4JH4-HTE
84 83.935
22 mm
Piston
bottom
008232-00E