Benjamin Hand Pump Maintenance, Modifications and Reliability

[bubba zanetti]

I thought I would start a thread regarding the Benjamin hand pump and chronicle my experiences with it and try and provide any technical insight into the care and feeding of this common PCP pump. Also, I wanted to document any upgrades or changes I made to the pump over time, how long it has lasted between maintenance needed and its overall performance.

First, the pump I have was bought used so I had no idea of its history as in how it was treated or if any maintenance was done, but upon its arrival it was clear the pump had seen use. Not in a bad way, just used.

I used the pump to do my initial sight in with the .25 Marauder and it felt like the pump was working a little harder than it needed to pump the gun up to 3000psi. I decided since I didn’t know the pumps history a couple rebuild kits from Sun Optics ($13.00 bucks shipped to my door) were in order. I didn’t want to keep using the pump until I had gone through it to verify its internal condition.
While waiting for the rebuild kits to arrive I read all the threads on the GTA and Marauder forum on the who’s, what’s and why’s of the Benjamin pump including upgrades (i.e. boosting) and general care and feeding. I also watched every YouTube video I could find on how to pull the pump down. This is great information and I didn’t post pictures of the tear down because they exist in so many places I thought it redundant. Besides, that isn’t quite what this thread is about.

A week later the rebuild kit arrived so I broke out the hand tools and began disassembly. One thing, Sun Optics proves a few extra O-rings, but not doubles of EVERYTHING. I have to say, the pump is very, very simple and comes apart with a minimal of hand tools. A few adjustable wrenches and I had it apart rather quickly. The only issue was unscrewing the valve from the final piston bottom was really hard as it was this pumps first time being disassembled. The videos are right, that was hard. But when you re-tighten the bottom valve to the internal piston you don’t torque the heck out it so you won’t have to face that again.

One thing was immediately clear; that little brass filter doesn’t filter &^^&! Well maybe it keeps out insects, rocks and small children walking buy while pumping but the pump was full of moisture and whatever grease used to lube the pump was black and nasty. As I tried to remove the black goo and moisture I started to go through rages quickly and the lube didn’t want to come all the way off. SO I grabbed my rubber gloves and took the parts to my garage and used a can of spray brake cleaner. That removed the nastiness perfectly! I went over each part after cleaning and inspected them closely. The machining in some spots is a little rough. I had removed the original O-rings BEFORE the brake cleaner was used and inspected them while I let the brake cleaner flash off the parts. Upon wiping off the black goo I was surprised to see the O-rings were still in very good shape! Even the common #007 O-ring that fails was PERFECT! I was tempted to re-use the O-rings but decided to start from new for my experiment.

Once all parts were cleaned and laid out with the proper O-rings. I began lightly applying the diver’s silicone grease lightly to the O-rings and installing them. When I mean lite I mean LITE!  That stuff is thick and gooey. You barely need any on your fingers to burnish the O-rings. I also applied on the main piston rod an even coating of 15 wt. 100 % percent silicone shock oil from the local hobby store. I also added a light coat of the silicone oil to some of the O-rings to assist in assembly. Before I knew it the pump was back together!

Now, the one mod I did do was add a desiccant filter. Lots of ways to do this, again pictures are all over the GTA and Marauder forum. I think this mod is needed in some form or fashion. You can get the filters from Harbor Freight, NAPA Auto, etc. I then went to ACE Hardware and spent 10 bucks in brass adapters and as you can see from the picture I know have a desiccant filter added to the Benjamin Pump. So for 20-30 bucks in filters and parts you can have a decent filtration system.

This past Sunday I used the pump in its rebuilt condition and all I can say is there is a major difference in its performance. It adds a little more air, runs cooler and smoother to boot!
So right now I am just going to use it and monitor its condition as I shoot this summer. I will start taking pictures of ANY changes I make or maintenance performed. Forgot to add, the first time I used the pump the gauge on the pump did not quite match the gauge on the M-Rod. After the rebuild now they do 

I think it’s safe to say it is NOT the best pump in the world, but it reminded me of the Marauder rifle itself. Rough around the edges in spots, but works overall if taken care of. Also, with some possible “custom” work made even more reliable and better. I may polish some internals but as not everyone has access to machining parts, let’s see how it does with regular upkeep.

So my first suggestion if you own one of these pumps is to put a filtration system on it…that appears to be a weak link.

To be continued…



BZ

[AmBraCol]

Thanks, Dan.  I'm not sure what pump I'm going to end up with, most likely the Benjamin since that's 90% of what they sell down here.  Air Venturi is the other option.  Anyway, thanks for your feedback on the rebuild.  A lot of folks complain about them, but I'm curious as to how many have taken the time to ensure they are properly assembled, cleaned and lubed.  The right attitude has a lot to do with our experiences as well.

[Sandspike]

Why wait?? Boost that pump and cut the pumping in half. Satisfy your lazy half and enjoy shooting twice as much.

[Frank in Fairfield]

I have had mine for two years.
I follow Tom Gaylord's instructions to the letter.
Use those knees.
Keep the shaft  lubed with silicone.
Yep I put the desiccant filter on (in the right direction) (The desiccant can be emptied, dried and re-used) too.
I have a compressor and a Guppy but I use the pump for the PRod and the 1701P.
Now that you have the .25 pressurized it will only take about 75 pumps to get it from 2000-3000psi.
Of course if you de-gas the gun to empty it will take more...
Stay safe and free.

[Sandspike]

Boost and do it in +-30.

[bubba zanetti]

1st update.

Shot 140 pellets Sunday during a very extended pest hunt on a dairy farm. This is the most I have shot the M-Rod in one sitting. It took roughly 60-65 pumps to get from 2000 psi to 3000 psi for 24 accurate shots.

If I did the math right that is 325 total strokes on the pump throughout the day.

Pump didn't miss a beat.

BZ

[bubba zanetti]

2nd update and 1st failure.

In defense of the pump, my last couple of shooting sessions I kind of torture tested the Benji pump. Lesson? Let it cool down. In Hot weather that means really let it sit for 10 or more minutes to cool IN THE SHADE! Also, when your desiccant filter beads turn pink, change the filter. I didn't and got a little moisture in the pump.

Pulling the pump down the only O-ring that failed was this one in the valve. seen here in the pics.




All other o-rings were still well lubed and in excellent condition. A new o-ring and 10 minutes later I was back up and running.

Why did it fail? Heat and it somehow grabbed and rolled the o-ring tearing it. I could not feel any issue it just would not fill past 700psi.

So let this pumps cool and take your time pumping. Pump lasted about 300-400 shots. That last 50 is when I beat on the pump and it didn't take much to roast that o-ring.

Now I am going to try for longevity and see what happens.

Till Next time

BZ

[45Bravo]

I will be watching this.
Sun optics sell a desiccant filter for $25 shipped for the pump,and is somewhat larger than the one you assembled.

[bubba zanetti]

Hey Bravo:

That was just it. The price of the Sunoptics kept me form buying it. The one on the pump came in a two pack for 20.00 at the NAPA auto store and Harbor Freight has them for 8.00 each which I might try one of those when the one on the pump is no longer good. Pretty sure the HF ones are a little bigger too.

If I change it I'll document it 

BZ

[bubba zanetti]

Boost and do it in +-30.

Kyle:

Not ignoring you but not interested in "boosting" the pump for a host of reasons. The main one being not everyone has the time, tools and talent to boost a pump. But they do have the time, tools and talent to maintain and repair a pump.

Its a great modification for those whom it will suit.

BZ

[BigTinBoat]

2nd update and 1st failure.

In defense of the pump, my last couple of shooting sessions I kind of torture tested the Benji pump. Lesson? Let it cool down. In Hot weather that means really let it sit for 10 or more minutes to cool IN THE SHADE! Also, when your desiccant filter beads turn pink, change the filter. I didn't and got a little moisture in the pump.

Pulling the pump down the only O-ring that failed was this one in the valve. seen here in the pics.




All other o-rings were still well lubed and in excellent condition. A new o-ring and 10 minutes later I was back up and running.

Why did it fail? Heat and it somehow grabbed and rolled the o-ring tearing it. I could not feel any issue it just would not fill past 700psi.

So let this pumps cool and take your time pumping. Pump lasted about 300-400 shots. That last 50 is when I beat on the pump and it didn't take much to roast that o-ring.

Now I am going to try for longevity and see what happens.

Till Next time

BZ

Are you saying the o-ring that seals the inner tube to the check valve body where it screws in failed? Not sure how that could "roll" during uses as that inner tube does not move, right?

[45Bravo]

I was just given a Benjamin pump, that I don't know the history of, and it does have issues as it is, and it doesn't have a fill hose.

(Hey the price is right, FREE)

It is going to sun optics Tuesday with a check, ($25 for a complete rebuild and refurb, $5 for a new fill hose with foster connection, and $25 for the filter)

So for $55 total, I get to start from a known point with a working pump.
And a filtration/dryer system.

[bubba zanetti]

Big Tin Boat:

I wish I could take better pictures because the tear in the o-ring was weird. In the short the heat from failure to let the pump cool deformed the o-ring and when I pulled the tube out of the housing that's when it probably caused more damage. Maybe I didn't use the correct language in describing the failure initially.

Its not the o-ring I thought that had failed that's for sure.

BZ

[bubba zanetti]

Nice deal Bravo! 55 bucks would work for me 

BZ

[BigTinBoat]

Big Tin Boat:

I wish I could take better pictures because the tear in the o-ring was weird. In the short the heat from failure to let the pump cool deformed the o-ring and when I pulled the tube out of the housing that's when it probably caused more damage. Maybe I didn't use the correct language in describing the failure initially.

Its not the o-ring I thought that had failed that's for sure.

BZ

Gotcha - it's usually the 007 on the end of the inner rod. Since that inner tube is threaded my guess would be that you probably "nicked" that ring on installation, which was then furthered by the heat.

What I found is that my pump moves easier and I seem to get lees heat since I went to 100% silicone "oil" for assembly instead of "grease". I used the stuff RC cars use in the differential.

and  45 - yeah $55 is a a deal, especially the $5 for hose with fitting. Heck the cheapest I found foster fittings was about $12 for a pair.

[bubba zanetti]

Big Tin Boat:

I wish I could take better pictures because the tear in the o-ring was weird. In the short the heat from failure to let the pump cool deformed the o-ring and when I pulled the tube out of the housing that's when it probably caused more damage. Maybe I didn't use the correct language in describing the failure initially.

Its not the o-ring I thought that had failed that's for sure.

BZ

Gotcha - it's usually the 007 on the end of the inner rod. Since that inner tube is threaded my guess would be that you probably "nicked" that ring on installation, which was then furthered by the heat.

What I found is that my pump moves easier and I seem to get lees heat since I went to 100% silicone "oil" for assembly instead of "grease". I used the stuff RC cars use in the differential.

and  45 - yeah $55 is a a deal, especially the $5 for hose with fitting. Heck the cheapest I found foster fittings was about $12 for a pair.

Yup, I have a Hobby Store in Seaford, Delaware were I got my 100% silicone shock oil for $4.50. You are correct, great stuff and it lubes very, very well. Don't need much 

I thought the 007 ring would be toast too, but looked great. The one Sun Optics now sells in the rebuild kit is a white one (the name of the material escapes me, Mac 1 uses these types of O-rings) and it was fine.

I will keep an eye out if I nicked that o-ring. I am usually pretty good about such things, but I love suggestions as its more to explore.

BZ

[BigTinBoat]

Yup, I have a Hobby Store in Seaford, Delaware were I got my 100% silicone shock oil for $4.50. You are correct, great stuff and it lubes very, very well. Don't need much 

I thought the 007 ring would be toast too, but looked great. The one Sun Optics now sells in the rebuild kit is a white one (the name of the material escapes me, Mac 1 uses these types of O-rings) and it was fine.

I will keep an eye out if I nicked that o-ring. I am usually pretty good about such things, but I love suggestions as its more to explore.

BZ

I was going to get the shock oil but it seemed too thin, that's why I went with the differential oil (I think the 5500w). Same oil just diff "thickness".
Also - I did not use the 2 o-rings on the rod, I made a "washer" from a nylon bushing to replace the white o-ring. Seems to be working better for me then using the white and black o-rings together from the "kit". That and a 90 duro viton ring seems to no long "roll".

[Frank in Fairfield]

BTW...
You do not have to change the filter (The ones from Harbor Freight).
Open them (Unscrew the caps), dump the dessicant onto an aluminum tray and heat in the oven aat 300 degrees til they turn blue.
An old toaster oven (garage sale item) works very well for this...

[45Bravo]

I thought since this a Benjamin product,
I called Crosman (since they own Benjamin) to see what their price was on servicing a pump either in or out of warranty.

Their response was that they don't do any servicing of the pump.
It would have to go,to the manufacturer, and they gave me sun optics number.

I called Duane Sorenson there and we talked about the pump, and what should I do to maintain it.
And I asked about lube.

He says when they assemble them, they use Mobil One pure synthetic oil.
And suggested that I use a drop or two of that on the outside tube for lube if any is needed.

I asked about silicone as a lube, he says that the Mobil One has a higher flash point than the pump, or PCP guns can produce.

I did find it interesting, that the manufacturer would suggest using something other than silicone that everyone else (end users) suggest..

But hey, they make it, and know a whole lot more about their product than I do..

Any thoughts on that?

[BigTinBoat]

I asked about silicone as a lube, he says that the Mobil One has a higher flash point than the pump, or PCP guns can produce.

I did find it interesting, that the manufacturer would suggest using something other than silicone that everyone else (end users) suggest..

But hey, they make it, and know a whole lot more about their product than I do..

Any thoughts on that?

The spec sheet I found for the Lucas Silicone oil I use says that it has a flash point of 572 deg F. Depending on the weight of the Mobil One I've found figures that vary in the 400-500 deg F range. I have no clue as to what temps the PCP or Pump can generate