2B•18 Engine removal and general overhaul procedures
12.7 Cleaning a cylinder head bolt hole in
the cylinder block using a tap
12.12c Piston classification on the piston
crown
be sure to clean all oil holes and galleries very
thoroughly, and to dry all components well. On
completion, protect the cylinder bores as
described above, to prevent rusting.
7 All threaded holes must be clean, to ensure
accurate torque readings during reassembly.
To clean the threads, run the correct-size tap
into each of the holes to remove rust,
corrosion, thread sealant or sludge, and to
restore damaged threads (see illustration). If
possible, use compressed air to clear the
holes of debris produced by this operation.
12.12a Piston and cylinder bore
classification code locations
Warning: Wear eye protection
when cleaning out these holes in
this way!
8 Apply suitable sealant to the new oil gallery
plugs, and insert them into the holes in the
block. Tighten them securely. Refit and tighten
the oil jets to the bottom of the crankcase on
B2O4/B234 engines.
9 If the engine is not going to be reassembled
right away, cover it with a large plastic bag to
keep it clean; protect all mating surfaces and
the cylinder bores as described above, to
prevent rusting.
Inspection
10 Visually check the cylinder block for
cracks and corrosion. Look for stripped
threads in the threaded holes. If there has
been any history of internal water leakage, it
may be worthwhile having an engine overhaul
specialist check the cylinder block/crankcase
with special equipment. If defects are found,
have them repaired if possible; otherwise, a
new block will be needed.
11 Check each cylinder bore for scuffing and
scoring. Check for signs of a wear ridge at the
top of the cylinder, indicating that the bore is
excessively worn.
12 The cylinder bores and pistons are
matched and classified according to five
codes - AB, B, C, 1 (0.5 mm oversize), and 2
(1.0 mm oversize). The code is stamped on the
piston crowns, and on the front of the cylinder
block (see illustrations). Note that all
12.12b Cylinder bore classification on the
front of the block
classifications may occur in the same cylinder
block.
13 Wear of the cylinder bores and pistons can
be measured by inserting the relevant piston
(without piston rings) in its bore and using a
feeler blade. Make the check with the piston
near the top of its bore. If the clearance is
more than the nominal (new) amount given in
the Specifications, a rebore should be
considered, and the opinion of an engine
reconditioner sought.
1 Before the inspection process can begin,
the piston/connecting rod assemblies must be
cleaned, and the original piston rings removed
from the pistons (see illustration).
2 Carefully expand the old rings over the top
of the pistons. The use of two or three old
feeler blades will be helpful in preventing the
rings dropping into empty grooves (see
illustrations). Be careful not to scratch the
piston with the ends of the ring. The rings are
brittle, and will snap if they are spread too far.
They're also very sharp - protect your hands
and fingers. Note that the third ring
incorporates an expander. Always remove the
rings from the top of the piston. Keep each set
of rings with its piston, if the old rings are to be
re-used.
3 Scrape away all traces of carbon from the
top of the piston. A hand-held wire brush (or a
13.1 Piston/connecting rod assembly
components
13.2a Removing a piston compression ring
with the aid of a feeler blade
13.2b Removing the oil control ring
A good alternative to
compressed air is to inject
aerosol-applied water-
dispersant lubricant into each
hole, using the long tube usually
supplied.