This New Holland skid steer loader arrived at the workshop with both the 4 Way bucket cylinder leaking oil badly.
At first we thought that it would be a case of the usual old collar seals on the top end of the cylinder.
After stripping the cylinders down though, another picture emerged.
Yes , the seals were leaking, but not necessarily because they were old and worn.
On close examination the shafts were badly worn in the middle and the chrome was damaged.
The straight edge solved the problem, the shaft were indeed bent!

But why?

Please examine the photos below and see whether you arrive at the same conclusion.

Notice the two chrome shafts, even with the eye one can see they are bent. Bend the shaft and the cylinder will leak.

But how did the shaft bend?
Spotted the clue in this photo?

Much more evident in this photo.

The cavity behind the cylinder fills up with soil and stones, and as the bucket opens and closes every time it compacts the soil into a solid wedge. The cylinder needs to travel inwards to open the bucket, but it cannot because of the compacted soil. The only way to keep moving is to bow the shaft in the cylinder, and after a few strokes the damage is done!

The new cylinder fitted, notice the freedom it has to move in compared with the previous photos. Yes the secret is to keep the cavity behind the cylinder clean, don't be shy to use the pressure washer!

How to deal with bent hydraulic cylinder rods

Checking rod straightness

Rod straightness should always be checked when a hydraulic cylinder is being re-sealed or repaired. This is done by placing the rod on rollers and measuring the run-out with a dial gauge (Figure 1). Position the rod so that the distance between the rollers (L) is as large as possible and measure the run-out at the mid-point between the rollers (L/2).

Checking Rod Straightness

Allowable run-out

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. To calculate maximum, permissible run-out (measured at L/2) use the formula:

Run-out max. (mm) = 0.5xL/1000
Where: L equals distance between rollers in millimeters.

For example, if the distance between the rollers was 1.2 meters, then the maximum, allowable run-out measured at L/2 would be given by 0.5 x 1200 / 1000 = 0.6mm.

Dealing with bent 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.
If a rod is bent, then it is wise to check actual rod loading against permissible rod loading based on the cylinder's mounting arrangement and the tensile strength of the rod material. The formulas and procedure for doing this are explained in detail on page 58 and 59 of Industrial Hydraulic Control. If actual road load exceeds permissible load then a new rod should be manufactured from higher tensile material and/or the rod diameter increased to prevent the rod from bending in service.

If you enjoyed this article, you'll love Brendan Casey'sInside Hydraulics newsletter. It gives you real-life, how-to-do-it, nuts-and-bolts, hydraulics know-how -- information you can use today.

Click on the logo below to read more on  bent hydraulic cylinders.

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