Service manual

G420F(FE) Service Manual Chapter 3. Engine Mechanical System
111
Class Piston outer diameter Size code
A
81.97~81.98mm
(3.2271~3.2275in.)
A
B
81.98~81.99mm
(3.2275~3.2279in.)
None
C
81.99~82.00mm
(3.2279~3.2283in.
C
8. Select the piston related to cylinder bore class.
Clearance
0.02 ~ 0.04 mm (0.00078 ~ 0.00157in.)
Boring cylinder
1. Oversize pistons should be selected according to
the largest bore cylinder.
Identification Mark Size
0.25 0.25 mm (0.010in.)
0.50 0.50 mm (0.020in.)
NOTE: The size of piston is stamped on top of the
piston.
2. Measure the outside diameter of the piston to be
used.
3. According to the measured O.D., calculate the
new bore size.
New bore size = Piston O.D + 0.02 to 0.04 mm
(0.0008 to 0.0016 in.) (clearance between piston
and cylinder) -0.01 mm (0.0004in.) (honing margin.)
4. Bore each of the cylinders to the calculated size.
CAUTION
To prevent distortion that may result from
temperature rise during honing, bore the
cylinder holes in the firing order.
5. Hone the cylinders, finishing them to the proper
dimension (piston outside diameter + gap with
cylinder).
6. Check the clearance between the piston and
cylinder.
Standard: 0.02-0.04 mm (0.0008-0.0016 in.)
NOTE: When Boring The cylinders, finish all of the
cylinders to the same oversize. Do not bore only one
cylinder to the oversize.
Piston and Rings
1. Clean piston
1) Using a gasket scraper, remove the carbon
from the piston top.
2) Using a groove cleaning tool or broken ring,
clean the piston ring grooves.
3) Using solvent and a brush, thoroughly clean the
piston.
NOTE: Do not use a wire brush.
2. The standard measurement of the piston outside
diameter is taken 47 mm (1.85in.) from the top
land of the piston.
Standard diameter
81.97 ~ 82.00 mm(3.2272 ~ 3.2283in.)