Hanson Hydraulics Ltd. Blog

Oilgear PVWH34 Pump Repair – Skidder Pumps

Posted by Doug Hanson - 16/08/10 at 07:08 pm

How To Build A Bullet-Proof Oilgear PVWH34. Written for Hanson Hydraulics Ltd. Blog: This is a reposting of the original aricle I had written for the first Hanson Hydraulics Blog. I get a lot of requests for it, so here it is reposted. I will add some pictures to it in the future, but in the meantime, here is the text: 

This repair applies to other models of the PVW* ** family of course, but this case pertains specifically to the Oilgear pumps used in John Deere and Timberjack skidders.  This is kind of a special case because there are a couple of “bizarre” steps that wouldn’t normally be done.

Step 1 – Rip it apart. Nothing needs to be marked.

Step 2 – Inspection. Go through a regular inspection looking for potential problems as discussed previously. Also pay special attention to: The easy start up valve in the port end cover. This consists of a fixed needle and a spring biased open seat. The moveable seat is aluminum and commonly washes out. These are not serviceable, just replace it.  To the best of my knowledge this will have to come from a John Deere dealer.

Contamination has a tendency to impregnate into the barrel bushing located in the housing of the pump.  If you see shiny things, replace the bushing. It is possible to reline these bushings, but way easier to replace it. This can come from a John Deere dealer or Oilgear distributor.

Inspect the fit of the control pin in the swash plate, this bushing often wears out.

Take the compensator apart, clean it out good with solvent and then brake cleaner, get all traces of oil and solvent out so that you can see into the compensator spool bore. Look at the area near the drill porting in the bore. If there is any wear, the compensator will need to be re-fit.  Check the small compensator spool for flat spots due to wear.  If present, get compensator refit.

Step 3 – Fix it up time.  One of the biggest problems these pumps experience at high pressure is the gasket giving out between the pump housing and compensator.  The pumps housing is machined and the mounting face of the compensator is Blanchard ground.  It usually is not very flat.  The even slightly uneven surface leaves part of the gasket unsecured as it is only “squished” in certain areas.  This is one of the repair techniques that would make most shops shake their heads, but I swear it works.  Lap the mounting face of the pump housing. You will have to stand there and hold the housing while moving it around and rotating it on the table. Stay there and hold it or it will start flying and banging around like crazy.  Do the same for the mounting surface of the compensator (scrape any paint away first). The compensator you can usually place in a steel ring and it should be fine on the table.  Lap them until you don’t see any low spots. Some shops will seal this mating surface with an anaerobic sealant, however once the mounting surfaces are dead flat, the gasket will hold.

An alternative method: The compensators pilot port interface at the housing/compensator joint is sealed with an oring sitting on top of the gasket. You could tap out the gasket around the edge of the oring groove; have a Teflon backup made to fit in the oring groove and then an oring to fit inside of the backup.  The backup will keep the oring from extruding into the gap created by the thickness of the gasket.

I have also seen other repair shops as well as some unit from the factory with roll pins installed as dowels to locate the compensator to the housing, this prevents the compensator body from shifting and tearing the gasket.

Lap the barrel face up.  Parkerize the barrel face only. Let the barrel face sink into the Parkerizing solution only ¼:” or the micro crystals will cause the piston bores to become smaller. It is salvageable, but it is a pain. Try not to do it. 

Lap the retraction plate, deburr the socket seat and then parkerize.

Lap the port end cover and then parkerise. (Should strip paint off before lapping and Parkerizing)

Lap the swash plate. This may take quite a bit of time. Once clean, parkerize.  The control pin bore will become tight after Parkerizing, so work until free.

Lap and polish piston shoes.

Grind chrome grind the shaft seal area. After you have successfully removed the shaft end bearing snap ring and have had time to calm down and regain your composure, grind opposing angles on the snap ring ends so that next time it comes off way easier with transmission snap ring pliers.

Always change the shaft end bearings.

Reinstall the old or new barrel bushing, but pay attention to which housing relief the roll pin will sit in If it is not in the right spot, when the barrel bushing rotates until it stops, the swash plate will arc up and bust off the roll pin, the bushing will then start spinning and they will be a nice little piece of roll pin to potentially cause harm.

If the unit has been in a fire, the barrel spring must be changed! It will not have enough tension and the barrel will lift off of the port end cover.

Be sure to install the long transfer pin into the compensator first and then the short stop pin. Remove the shims for testing, as it should be tested to 3500 psi and then reset to 3000.

When reinstalling the compensator on the pump, do so with the spool spring cover loose (pitch the original oval headed socket head cap screws and replace with hex head cap screws ¼” longer and lock washers). Once you get the control pin engaged to the control piston and the four mounting cap screws started, torque the six cap screws first on the spring cover, and then torque the four mounting cap screws.

Replace the saddle bearings with steel backed Teflon bushings.  There may be a plastic bearing with the corners knocked off, this can be replaced with the standard sharp cornered steel backed Teflon on the 34 size.

The swash plate saddle bearing areas should be deburred at the edges so they can’t gouge into the bushings.

When testing it is important to break these bushings in gently, back the compensator right off, increase load to compensate, back it off again and repeat a couple of times.  Increase the compensator setting, and repeat every couple hundred psi until you get up to 3500.

After testing, reinstall pressure limiting shims (optional) and reset to 3000 psi.

Written for Hanson Hydraulics Ltd.

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