Fixing a hydraulic pump, lapping or no?

WeirdDeere · Dec 2, 2015

I'm working on a Deere two cylinder power steering pump, replacing seals and such.

Would it be a good idea to slightly lap the sealing surfaces of the pump? I have a feeling it's better to leave it alone, but thought I'd ask

The pump was only leaking out the shaft seals, the surfaces seem fine, I just wondered how much warpage there might be from years of being bolted together. One side of the pump has a pair of dowel pins that I'm going to have to leave in place...

I don't have any flat gauge block or anything fancy, I honestly was going to tape fine sandpaper to glass.

Brandon

Dan in Ohio · Dec 2, 2015

Brandon,

The PS pump I rebuilt this summer seemed to need lapping, so did just as you have said. The problem I ran into was what I used on them when I put it all back together. Next time I will not use anything like Indian head shellac. Think I will just use a thin coat of oil. Had to take mine apart and basically remove the shellac, just could not make it thin enough.

Dan in Ohio · Dec 2, 2015

Photo was to document the dinged up bushing, but was surprised by how rough the plates were. Have seen power trol pumps that looked a lot better.

WeirdDeere · Dec 2, 2015

Wow, mine's definitely not that bad haha

Did you just lap around the pins in place? What grit did you use?

Brandon

Dan in Ohio · Dec 2, 2015

Used a flat piece of bar stock as a sanding block with 400 grit paper and some light weight oil and did not remove pins. First time reassemble used the shellac, turned the shaft a few times then tightened everything up. Next day whole thing was seized up had to start over. Did not use much shellac first time either.

WeirdDeere · Dec 2, 2015

Thanks for the opinions on this, I'm glad someone else has done it, I just didn't want to screw up my decent pump by messing with it! I get too enthusiastic or picky sometimes!

Brandon

Dan in Ohio · Dec 2, 2015

Brandon,

I read ever post I could find on the subject when working on this and found some great guidance on the seal installation and the pump in general. Did as F-I-T suggested as far as lapping and reassembly. Others suggest using Honda bond which I could not even find but I had shellac and tried to do as instructed (use very sparringly). FIT said lap so that the plates stick together with a thin coat of oil applied. That would be my advise.

Steve@Advance · Dec 2, 2015

If the dowel pins won't come out, trying to lap it will be impossible, could even do more harm than good. It shouldn't be warped just from being bolted together. Warpage usually occurs when there is a thick gasket between the surfaces, it was over torqued, or assembled dirty. Since none of this has happened, and it wasn't leaking, I would just concentrate on getting it clean, go back with very thin application of sealer, should be OK.

DLMKA · Dec 2, 2015

flatness tolerances on hydraulic pumps are really low, down in the micron range. If you can't get those pins out you're going to do more harm than good trying to lap it. run a finger across and carefully buff off any burrs that would keep the sections from seating properly. The end clearance on a gear pump is the largest driver of pump efficiency as well as durability. There is a a fine line between too much clearance and too much fluid slip across the gear faces reducing efficiency and possibly even pressure capability of the pump. Too little clearance and you can run into scuffing issues that will stick a pump or completely destroy it. Debris sensitivity comes into play here too.

I've seen gear pumps with the faces of the gear teeth worn so bad they were concave instead of convex and the lash was terrible but the end clearance hadn't worn at all and the pump still worked fine. No indication from the operator anything was wrong, pump came back to me for 20,000 tear-down inspection.

Bob · Dec 2, 2015

Clean it up REAL nice and use a TINY amount of anaerobic sealing compound and you will have NO problems.

One thing I do is scraping the marks/debris off of the surfaces with a single-edged razor blade held at 90? to the surface.

I have done a number of those very pumps that way with NO leaks or issues.

<img src = "http://ecx.images-amazon.com/images/I/31FSNeYK24L._SY355_.jpg">

WeirdDeere · Dec 2, 2015

The pump did seem to make good pressure, I don't remember where it was, it wasn't up to new specs. I did find a little bit of wear, scoring and pitting on one face of the pump. I found the cause and have fixed it. The gear was supposed to float on a keyway, but the keyway was worn, allowing it to tip and bind the floating.

<a href="http://s108.photobucket.com/user/weirddeere/media/80PowerSteering/PumpGearWear_zpsd6rtfyvu.jpg.html" target="_blank">

PumpGearWear_zpsd6rtfyvu.jpg" border="0" alt=" photo PumpGearWear_zpsd6rtfyvu.jpg

</a>

I hope this isn't enough wear to affect it too much.

Thank you for the basic info on the pumps, I always thought the tooth clearance was the killer of pump pressure/flow!

Brandon

Fixing a hydraulic pump, lapping or no?

WeirdDeere

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Dan in Ohio

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Dan in Ohio

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WeirdDeere

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Dan in Ohio

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WeirdDeere

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Dan in Ohio

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Steve@Advance

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DLMKA

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Bob

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