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Section 4 Engine Service
ensure the piston is installed in the proper direc-
tion. Push the piston pin through the piston and
connecting rod and secure it with new retainers.
See Figure 19-8.
Checking Ring End Gap
The inside diameter of a piston ring is always
made smaller than the piston’s diameter. This
being the case, each ring must be expanded to get it
over the piston head and into the ring groove. The
amount of end gap is critical and should match the
manufacturer’s specifi cations. As a rule of thumb,
however, allow .004″ of end gap for every inch of
cylinder diameter. For example, the minimum end
gap for a 2.5″ cylinder is .010″.
Too much end gap will allow the gases to leak
between the ring ends. Too little gap is even more
serious. When the rings heat up in service, they
will expand and close up. If the rings continue to
heat and expand, they will break and score the cyl-
inder wall.
To measure ring end gap, place the ring in the
cylinder. Then, turn a piston upside down and
push the ring to the lower end of the cylinder.
When the ring reaches the proper depth, remove
the piston.
Select a feeler gauge blade that is thinner than
the gap to be measured and place it in the gap.
See Figure 19-9. Progressively use thicker leaves
until you can feel a slight contact or drag from the
gap’s edge surfaces. At this point, compare the leaf
Figure 19-7.
Some engines have a centrifugal governor gear or oil
slinger installed on the camshaft.
Oil slinger/governor
Figure 19-8.
Check the marks on the piston head and connecting
rod to ensure that the piston head is reinstalled in the
proper orientation. A—Install the piston pin. B—Install
the piston pin retainer.
A
B
Figure 19-9.
Ring end gap is measured by pushing the ring into
the cylinder with an inverted piston. Then, the piston
is removed and a thickness gauge is used to measure
the gap.