This information was taken from
http://www.insidersecretstohydraulics.com/...-cylinders.htmlHas been editedHydraulic cylinders - checking rod straightness
Many hydraulic equipment owners or their maintenance personnel repair hydraulic cylinders in-house. An important step in the repair process that is often skipped by do-it-yourself repairers, is the checking of rod straightness.
How do bent rods affect hydraulic cylinders?
Bent rods load the rod seals causing distortion, and ultimately premature failure of the hydraulic cylinders seals.
Allowable run-out
Rod straightness should always be checked when hydraulic cylinders are being re-sealed or repaired. This is done by placing the rod on rollers and measuring the run-out with a dial gauge. The rod should be as straight as possible, but a run-out of 0.5 millimeters per linear meter of rod is generally considered acceptable.
Straightening hydraulic cylinder rods
In most cases, bent rods can be straightened in a press. It is sometimes possible to straighten hydraulic cylinder rods without damaging the hard-chrome plating, however if the chrome is damaged, the rod must be either re-chromed or replaced.
Editors note:
We used to just mount them in a vise, use a pipe and big hammer to straighten them. It could be done, and wasn't all that bad. 
