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[RayK]

I'm waiting to get my hand pump to rebuild.

I have been reading and it sounds like silicone grease does not work well as a lube. It primarily keeps orings plyable.

It seems like krytech or moly might work well for lubricating hand pumps. Has anyone tried any of these?

Any guesses if it would be good or bad?

One guy who worked for sun optics recommends non detergent motor oil, but I would think these would be better. And I'd rather avoid dieseling explosions.

Ray

[ShawnHu]

Full synthetic motor oil is not a problem and has been recommended.

Whatever you use, make sure it's synthetic. It'll keep the o rings in good shape and won't diesel. If you don't have one already, give Dwaine a call and ask him to sen you a rebuild kit. It'll have the new upgraded P90 o ring.

[RayK]

Is Duane the guy at SunOptics? I imagine P90 means it is 90 Durometer which is a firmer o-ring than the typical 70 Durometer.

Is it usually that 007 o-ring on the bottom end of the thin rod that goes? Are there others that go too?

I heard one guy say it is difficult to get Benjamin pumps resealed after a rebuild, but I wonder if that is because he used old o-rings or maybe under-spec o-rings. I also found one guy who said moly gummed up his hand pump, but maybe he over lubed it. It is easy to do....

While searching, I found these instructions for Hill pumps which makes it sound like silicone grease is all they use.

Maintenance of pump

• After prolonged use the pump may become harder to operate. This can be caused by a blocked filter; lack of lubrication; or a build up of previously applied lubricant causing friction of seals and rod.
• The pump has a specially designed micron filter to prevent excess moisture, oil, grease or contaminants from entering the cylinder when charging.
• This filter is easily replaceable and should be changed when it becomes clogged or after extensive use. Spare seal and filter replacement kits are readily available.
• It is recommended that the pump is occasionally cleaned and lubricated for long life and ease of use. Lubrication should be applied onto the pump rod and then pumped for a few strokes.
• The pump is factory lubricated using silicon grease.
• Do not use Petroleum based Lubricants.

[RayK]

I also found this:

"Do not remove any lubricant from the pump shaft. This lubricant is dark and will stain clothing, but it is NOT moly grease as many people have supposed. If you remove it, your pump will soon fail."

So it sounds like the Benji pump is factory lubricated with a dark lube that will stain clothing that is NOT moly. Sounds like moly to me

And this sounds like great advice for pumpers:

Take a shot at rebuilding your current pump. 9 out of 10 times, it's is that final outlet/check valve o-ring that is either clogged or fried. Often get clogged, whatever lube they use can get whipped up/melted/ (emulsified?)..I just call it air-pump-snot.
-----------
Didn't ask for this, but am going to put it here anyway in hopes it helps someone reading the post. to keep your pump alive, you can't be in a rush..if you are in a hurry to shoot, buy a tank.

Pumps die by heat, it cooks that final o-ring and promotes "air gun snot" issues. So this is my drill, which has kept the pumps alive.

1. Hook up, and pump 50-60 stokes.
2. VENT. Can leave hose attached, just vent all the pressure in the line and pump.
3. Cool down rest period..will take 5-10 min and go get a Coke or some coffee.
4. Pump another 50-60 stokes.
5. Vent.
(repeat as needed to get up to your fill).
...
Whatever the Hill was lubed with became a gray gunk that clogged the check valve and final filter. Probably could have gotten away with just taking it apart and cleaning out the slimy gray gunk, but I figured as long as I had it all apart, may as well replace the o-rings. Reassembled with dry lube on the metal parts, silicon grease on the o-rings, and have been working fine for a couple of years now.

(Has the dry pac...mark me down as a non-believer, don't believe the dry pack removes enough moisture to really matter.)

Yes, believe bleeding the line every 50-60 pumps expels moisture. Have been inside all the PCP's, all of them hand pumped, and the only rust found was in a brand new rifle (so the rust was in there before I opened the box).

Ray

[ShawnHu]

Ray, Duane is the inventor of the Benji pump, if you will. He recommends silicone oil, not grease and synthetic motor oil is ok as well.

Yes, the 90 durometer is the new whitish o ring being used instead of the black 70 ones. Stiffer and more resistant to wear. The 007 is the only I ring you need to replace for a LONG time. Sealing the Benji pump after rebuild only needs H&N tighten with tools, much looser than factory.

[ShawnHu]

Ray, the oil on the piston is silicone oil, but after use, turns black from the o rings wearing out. It's no big deal to wipe this, as the main o ring that fails is internal, and has nothing to do with this layer of lube. You will however, end up replacing the outer o ring sooner if the piston has little to no lube.

[RayK]

Thanks Shawn. I will get some (non petrolium) silicon oil.

Ray

[ShawnHu]

No sweat Ray, dive shops or direct from Crosman.