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Damaged Final Drives: Radial Piston Motors

by Dr McCaslin | Mar 15, 2021 | |

This post continues to look at damaged final drives by focusing on radial piston motors. Learn what kind of damage they can experience and how to extend their lives.


Damaged Final Drives_ Radial Piston Motors

Here are a few other Shop Talk Blog posts you might be interested in:

Rotator Assembly

The best place to start with this foray into damaged radial piston final drive motors is to look at a rotator assembly. In this picture taken in the shop you can see the rotator assembly (complete with its cam ring, pistons, and rollers). The cam ring is extremely scarred and not all pistons have rollers on them any more -- in fact, you can see where some of the rollers are trapped inside the cylinder block. Needless to say, that is never a good thing.


This image is a good overview of what serious damage to a radial piston hydraulic motor can look like.

Cylinder Blocks

This is a failed cylinder block with a piston trapped inside and no real sign of the roller. This will lead even more damage within the cylinder block. This particular cylinder block is beyond repair and would need to be replaced.


And here we see, in the same cylinder block, there is a roller that has turned sideways and has experienced a significant amount of edge damage. This is definitely not a good sign!


Here is another severely damaged cylinder block which is obviously beyond repair. Our team determined that all of this damage started as the result of hydraulic contamination. And there is no doubt that after this kind of damage it produced significant amounts of generated contamination. You can see how almost all the edges look chewed up.


It's important to keep in mind that modern hydraulic motors and final drives are far more sensitive to hydraulic contamination than older ones.

And here is a closeup so you can get a better look at the damage wreaked on this drive motor by contamination issues. This is a serious reminder of the importance of minimizing the contamination that makes its way into your drive motors.


Cam Rings

Below is a cam ring with some severe  surface damage in the form of pitting. This compromises the performance and efficiency of your drive motor.


On the same cam ring can be seen an hour glass shape on the raised portion of the ring, again indicating excessive wear. The original factory finish on these cam rings has a wavy appearance but not an hourglass shape. The two images below are a bit more clear.



Pistons and Rollers

Here are a set of three pistons: the one of the left might still be repairable, the one in the middle is what a typical one should look like, and the one on the far right is too far gone for reasonable repair. 


And here we have a trapped piston and a roller that has been turned sideways, both from the same drive motor. This is obviously a sign of major damage.




The number one cause of damage in radial piston hydraulic motors is contamination. There are ways to prevent contamination and mitigate the damage it causes that include ...

  • Regularly changing hydraulic filters
  • Using clean hydraulic fluid (and filtering it beforehand, if feasible)
  • Avoid opening up the final drive motor when it is dirty
  • Keep the work area clean when performing maintenance and repairs on hydraulic components
  • Never ignore leaks or worn out seals

Visit the Final Drive Shop for all of your hydraulic final drive motor needs!

Want some help figuring out what's wrong with your final drive?  We've got you back with an eBook

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