37
Group 21 Short block
Piston ring inspection and
adjustment
1. Remove the piston rings with piston ring pliers.
2. Remove the gudgeon pin circlips and remove the
gudgeon pin carefully, with a suitable mandrel.
3. Check that the rings do not bind in the ring
grooves.
4. Check the piston ring gap. Push the ring down be-
low the lower turning point with a piston.
Change the piston ring if the gap exceeds 1.0 mm.
Check the piston ring gap with new rings. Please
refer to the “Technical Data, specifications” chap-
ter for measurements.
In general, piston rings should be changed if there
is any noticeable wear or out-of-roundness in the
cylinders, since the piston rings frequently do not
end up in the same positions as they had before
disassembly.
Oil consumption is also of decisive importance for
the point in time when a piston ring change should
be done.
5. Check the clearance in the piston ring grooves.
Roll the ring in its groove in the piston, and mea-
sure the clearance at several points with a feeler
gauge. Please refer to the “Technical Data, speci-
fications” chapter for measurements.
Inspection and measurement of
piston and cylinder bore
Check the pistons for cracks and worn piston ring
grooves. Change the piston if it has deep grooves in
the skirt surface. Likewise, if the piston has one or
more cracks in the gudgeon pin hole. If any such
damage is found, the injection equipment should also
be checked.
Measure the piston diameter with a micrometer at
right angles to the gudgeon pin hole and 10 mm from
the bottom edge of the piston. Then measure the cyl-
inder bore and calculate the clearance between the
cylinder and piston.
Replace the piston if the clearance exceeds the per-
mitted or if the piston diameter is less than permitted
value.
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