Perkins 4.108 Workshop Manual page 46

PISTONS AND CONNECTING RODS-F.S
Where pretopped pistons are used, then the piston
height can be slightly lower than the limits given.
It is important to note that where vehicle engines have
to conform to the smoke density regulation B.S.AU
141 a: 1971, then the piston height production limits
must be maintained.
It will of course be appreciated that grade F pistons
are suitable for topping to give other grades where
these are not to hand.
After fitting pre-topped pistons, the distance between
the cylinder block face and p:ston crowns should be
checked to ensure the limit is as already quoted (See
Fig. F.12).
4.108 Vehicle Engines
Production Grade
A
to
F
G to L
M to P
4.99 Engines
Production Grade
B, D,
&
F
H, J, & L
N & P
Equivalent Service Grade
F
L
P
Equivalent Service Grade
F
L
P
F12