Toro 51643 Service Manual page 55

Engine Inspection (cont'd)
4.
Cylinder Bore
Use a bore gauge to measure the cylinder bore. By
itself, this measurement does not indicate much,
however
it
is important in determining the piston to
cylinder clearance. The cylinder can be used until
the chrome plating on the bore
Is worn away
("Exfoliates").
5. Piston Diameter
Use a micrometer to measure the diameter of the
piston in several places, recording the largest. As
with the cylinder bore measurement, this
measurement is important only in determining the
piston to cylinder clearance.
6.
Piston to Cylinder Bore Clearance
maximum allowable clearance
0.100 mm
(.004')
The difference between the recorded piston outer
diameter and the cylinder bore measurement is the
clearance. If the difference is greater than the
maximum allowable clearance, replacement of the
piston, piston pin and needle bearing as a set is
recommended.
Engine Reassembly
All parts, even if new, should be thoroughly cleaned.
Make certain all parts have been inspected and are within
specification.
Do not use worn and damaged parts. Use of worn and
damaged parts may cause personal injury and engine
failure.
1.
Use finger pressure to install the two piston rings
on the piston.
IMPORTANT The hemispherically notched
ends of the rings match the locating pins in
the
ring grooves. Also note that the top
side
(toward piston crown)
of
the ring is stamped
with a
'T.
See Figure
106.
2.
3 .
4.
5.
6.
7.
8.
9.
Figure 106
Install one of the piston pin retaining rings in the
piston.
n
Insert the upper connecting rod bearing into the
connecting rod.
Install the piston on the connecting rod by lightly
lubricating the piston pin with clean engine oil,
positioning the piston onto the connecting rod and
pushing in the piston pin. If necessary, the piston
pin can be driven into place by lightly tapping the
pin with a hammer and a non-marring punch or dr
pin.
Install the remaining piston pin retainer.
i f the main bearings have been removed, install the
new main bearings into the crankcase.
Lightly grease the lips of the crankcase oil seals to
prevent seal damage when the crankshaft
is
installed.
Carefully install the crankshaft with attached
connecting rod and piston into the crankcase
halves.
Use sealant Three Bond 1104 Foro part number
505-80) on the gasket between the crankcase
halves. Position the gasket between the crankcase
halves and assemble the crankcase halves with
connecting rod and attached piston.