Benjamin Marauder Pistol Leaking from Pressure Guage

[Dave_R]

I've had this Marauder pistol for around 7 years. It started leaking about a year ago. Just ignored it. It would lose most pressure overnight.

Finally diagnosed it with soapy water--leaking from where the pressure gauge screws into the reservoir tube. I have tried 4 ways to seal it--no luck:

-Re-install with yellow gas tape on the gauge threads.
-Re-install with blue loctite on the threads.
-Re-install with both yellow plumbers (gas) tape and blue loctite on the threads.
-Put an o-ring at the base of the pressure gauge.

The leak remains in the same place--right side of the threaded port that the guage screws into, when shouldered and looking down the barrel.

Any suggestions on a way to seal this leak? Should I try a caulk product, or a marine sealant like 5200 or 4000?

 

[SteveV]

It could possibly be the gage port o rings causing the leak and not the gage itself? And spell check won't let me spell gage with a "u"

 

[Dave_R]

Thanks for the reply, Steve. The gage port did not have an o ring installed from the factory. I tried one, but it didn't help.

OTOH, I torqued the gage on hard enough to really deform the o ring--it was poking out way more on 2 sides that in the center. Still leaked the same. And when I pulled the gage again, the o ring looked pretty ragged. Maybe I should try a new o ring with less torque?

The sopa bubbles indicate the leak is coming from the port the gagfe screws into--not the gage itself.

 

[Ranchibi]

With gauges, a little silicone grease on o'ring and snug tightening should suffice. If you tighten too much the o'ring deforms too much like you noted....

 

[Frank in Fairfield]

Behind the gauge there is a weeper hole.
When the gauge goes bad (they all do and you should keep spares) that is where it will fail!

 

[Bngen3]

There is no delrin washer between gauge and port ?

 

[Airgun-Revisions]

Your mistaking the leak. It’s actually coming from the gauge block o-rings. The thread would not leak after this many years. Only the rings would.
Now that you used soapy water you definitely need to take the gun apart or send it to a reputable shop. I say this because the longer the soapy water sits inside the block up around the inside of the tube it will definitely start rusting and pitting the steel. Then your guns shot.
-113 o-rings. Don’t use horrible freight O-rings.

 

[Dave_R]

There was no delrin washer between gage and port. Am I missing a part? I do not see any o rings in the gage block. Actually, I don't see a gage "block." Just a threaded hole in for the gage in the pressure tank.

AKAIK, no soapy water has entered the pressure tank, or even the gage threads. I only used the soapy water when the gage was in place, and the pressure tank pressurized. The pressure will keep any water from entering the block or tank.

Frank, I will defnitely get a spare gage! What's the best source?

 

[JimD]

I've never purchased a gage for my Prod but the few parts I have purchased from Crosman were very reasonably priced and delivered quickly. As I remember it, you pretty much have to call them. They may want you to give them a part number from their diagram but I think you can get it on their website.

 

[Airgun-Revisions]

There was no delrin washer between gage and port. Am I missing a part? I do not see any o rings in the gage block. Actually, I don't see a gage "block." Just a threaded hole in for the gage in the pressure tank.

AKAIK, no soapy water has entered the pressure tank, or even the gage threads. I only used the soapy water when the gage was in place, and the pressure tank pressurized. The pressure will keep any water from entering the block or tank.

Frank, I will defnitely get a spare gage! What's the best source?

Yes there is. This is the part your gauge screws to and is inside of your tube. And like I said – 113 O-rings. You do not have any washer on the bottom of this block because your gun is too old for the changeover that was 2 1/2 years ago. And yes it will rust out if you use soapy water because between the two O-rings there is a dead space of air there is pressure on both sides or it would leak out like it’s doing to you.

 

[Dave_R]

Airgun-Revisions--Wow! 113 o-rings!

I think we're looking at different parts of the P-Rod. The leak is where the pressure gage (item 44 on the diagram, part no. 1763-033) screws into the reservoir tube (item 42). The parts diagram does not show any o-ring there. Maybe there should be 114 o rings...

I tried (again just now) putting an o ring on the base of the pressure gage, but because it is mating to a curved surface on the reservoir tube, there's no way to get unform contact with the tube. There's always a gap at 3 o'clock and 9 o'clock, when you have firm contact at 12:00 and 6:00.

Does that make sense?

 

[jarmstrong]

Dave_R
Airgun-revisions has given you spot on advice, the piece in his drawing is inside the tube
the 3 and 9 o-clock positions are on the curve of the piece and just look funky, I believe that they are tapered threads for the gauge, tapered threads seal in the threads, use teflon tape.
Air-gun Revisions sells these guns for a living,,, his 20 cal Marauder has me tempted

Shop Categories - Airgun Revisions

www.airgunrevisions.com

 

[Dave_R]

Now I get it. So part 38A on the drawing is INSIDE the reservoir tube, and the port right by the arrow at 38a is actually what the pressure gauge screws into, right?

I'm still missing something, mentally. If part 38a is inside the tube, and the pressure gauge screws into it, then it must allow pressure to enter the gauge. Its not sealing pressure away from the gauge. And if the leak is in the threads of the gauge, then how do the o rings (38b) prevent leak from the threads of the pressure gauge? They're not keeping pressure away from that...

But I WILL try the teflon tape on the threads.

 

[jarmstrong]

it is the 38B o-rings that need replaced, the threaded hole in the port 38A is a close fit to the tube and air leaking by the o-rings will come out and appear as if it was coming from the threads,,, it all needs to come apart,,, and the gauge will need new tape also. now
the drawing does not show the threads in 38A, but they are there
7 years old,,, it is the best bet,,, it is the o-rings and the question is ,,, are you inclined to do the repair yourself?

 

[Dave_R]

jarmstrong, yes, I'm inclined to do that repair myself. I DIY as much as I can.

OTOH, the most important part of DIY is knowing when to let the pro's do it. Is this the kind of repair that a reasonably good DIY guy can do?

 

[Frank in Fairfield]

I sold all of my PCP rifles/pistols.
Just PRod left.
Every time I would order parts from Crosman, I ALWAYS added another gauge.
If you have them, you will not need them…

 

[JimBentley]

I have had over 10 gages fail. I keep a spare or two. The Burdon tube is constantly in motion when you shoot/fill the gun. the flexing eventually makes them leak.