When a gland requires packing, it is proper to take out all the old packing that has become hard and set.
A leak in piston rod packing may sometimes be remedied by taking out three or four rings of the packing and reversing it.
If the packing is tightened up while the engine is running, it should be done very gently and evenly, as a very little screwing up may stop the leak, while excessive screwing produces undue friction.
Piston rods are in some of the most advanced practice packed with metallic packing, or packing composed of soft metal. In some forms of metallic packing the construction is such that the gland and packing do not attempt to restrain the line of motion of the piston rod, this duty being left to the guide blocks and guide bars, where it properly belongs.
THE CROSS HEAD.
In engines having Corliss frames, the cross head is provided with shoes and adjusting screws, to take up the wear.
When guide bars are shaped thus
the cross head is provided with gibs (usually of brass composition) to take up the wear.
In either case care must be taken to make the adjustment correct, and thus keep the piston rod in line. The shoes or gibs should not bear hard upon the guides, but be an easy sliding fit without lost motion.