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     A lot of hydraulic pumps and motors use pistons with rings, which sometimes need to be replaced. Even though this is a common overhaul procedure, there are still a lot of "mispractices" present as far as the piston rings replacement is concerned. This simple operation, when performed inadequately, can result in piston damage and even personal injury, along with taking unnecessary amounts of time.

   I would like to show here the simple technique of piston ring replacement I've been applying for years. The "secret" lies in using a small piston ring expander, which can easily be made out of an old pair of snap-ring pliers (see the pictures to the left). This may not be the best method, but it's fast, safe, and have worked so far. I've created a small video, in which I show how to use the tool. And also - a list of "ring-handling" tips:

- To make the tool use a pair of snap-ring pliers with as little play in the articulation as possible.
- To make the expander you see on the pics, I used an angle grinder with a thin cut-off disc, although any other similar tool will do. Be patient when shaping the small tips - don't overdo it!
- Don't worry if it doesn't come out pretty - your goal is to make if functional. 
- When handling piston-rings, avoid snapping them into the piston grooves - always try to "catch" them with the expander, like I do in the video. It's ok to do so with small ones, but the big rings can chip the piston when "snapped on".
- Avoid opening the piston rings more than necessary - they're strong, but "breakable".
- Protecting your eyes is a nice idea.
- In the video I use a pocket knife to open the gap in the piston ring - the knife is blunt! Don't use sharp stuff for the purpose (unless you're fond of bleeding fingers).
- Make the tool in two or three sizes, and use the small one with small rings, and the big one - with the big ones.
- Remove and mount the rings in the order I do in the video.

    So, next time you come across someone in a workshop, trying to work the piston rings out with a small screwdriver, injured fingers and a lot of swearing - please, direct them to this page.