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Page J3
Pistons and Connecting Rods-continued
Fitting New Pistons.
It is important, when fitting ncw pistons, to
check the distance from the crown of the piston to
the face of the cylinder block.
l
When the crank is at top dead centre the crown
of the piston must be .007 to .012 in. (.178 to .305
mm.) above the face of the cylinder block. If the
piston stands higher than this then the crown must
be reduced by taking the necessary amount otT in
a lathe. If the piston height is below the minimum
figure quoted above, that piston must be rejected
if a first class performance is required.
(J~
To take this measurement the piston assembly
and connecting rad must be fitted to tbe cylinder
block and crankshaft as previously described.
When assem bied turn crankshaft to bring piston
to T .D.C. and place a straight edge across the top
of the piston and with a set of feeier gauges,
measure tbe distance between the straight edge
and tbe top face of the cylinder block.
(SeC'
Fig. J.4).
Connecting Rod Weigbts.
The finished weight of connecting rods in engine
sets should balance within two ounces.
In order to effect this, rods are batched as
follow~ :
Code
Minimum
Maximum
No.
I~'eight
Il'eight
12 4 Ib. 10 oz. (2.10
kg.)
4 Ib. 12 oz. (2.15 kg.)
13
4 Ib. ]2 oz. (2.15 kg.) 4 Ib. 14 oz. (2.21 kg.)
14
4 lb. ]4 oz. (2.21 kg.)
5 lb.
(2.27 kg.)
When fitting pistons and connecting rods to
cylinder block and crankshaft, ensure that the si de
of the connecting rod which is stamped with the
number goes to the camshaft side of the engine'
Insert the pistons and connecting rods into the
cylinder bores from the top, ensuring that piston
and Tod stamped No. I are fitted into No. I
cylinder bore and No. 2 into No. 2 cylinder bore
and so on counting from the front of the engine.
When fitting assem blies, deal with them in the
order land 4 then 2 and 3. Turn the crankshaft
until the appropriate crankpins are at B.D.C.
To minimise the possibility of breaking piston
rings, it is advisable to use a piston ring guide.
Take care not to damage the rings.
Should
the piston accidentally
drop
partly
into
the
bore and is held suspended by a piston ring, it
must be taken out again and the ring examined to
sec if it is cracked or broken.
Pull the connecting Tod to the crankpin and
insert the half bearing.
Fit cap and cap half hearing.
NOTE.
When replacing connecting Tod set-
screws, new locking
washers must always be
used.
The top and bottom half-shelis are not inter-
changeable with each other, due to the locating
lips of
the two
half-bearings being offset in
relation to one another.
Tlghten connecting Tod setscrews, using a torque
wrench set to the tension given in Section B.
It is necessary, therefore, when ordering spare~
for an individual engine that the appropriate code
nurnber of the connecting rod set be quoted.
This code number can be found etched either on
Nos. I or 4 connecting rod on the machined
shoulder which is adjacent to the fuel pump side
of the engine.
Cn spare rods, however,
tbe code
nurnber is
present on each rod.
Fig. 14. Checking di stance between straight edge and
cylinder block facc.
]
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