If one is going to overhaul a hammer, be sure to use new parts. Do NOT re-chrome the piston and repair the bore, other than maybe just cleaning up a minor stratch or two.
Outfit I worked for, the corporate equipment manager got a "hot" deal on a used hammer for the job I was on. Yep! You guessed it, the piston had been re-chromed and the piston bore had been welded up and rehoned. Both repairs quickly fell apart under use and the metalic debris went all through the excavator hydraulic system, creating a 60 thousand bill for cleaning, flushing, and replacement of seals and other parts damaged. That's when the order went out that the hammers we were using were to be used for hammering only, nothing else.
The 9 grand the CEM paid for that hammer in the first place became a lot more when all the cost were tallied. Not to mention the fact that I had to scramble and find another big hammer, and an excavator to put it on. Not too many available then in that area.
The original hammer was junk, it was not a common brand and parts were very expensive, with long lead times to procure. No doubt why the original owner repaired it the way he did and then got rid of it.