Marauder dumped air

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Marauder dumped air

Postby Rodent Slayer » Sun Feb 04, 2018 9:09 am

New member here.
I have been a long time fan of Benjamin products. I have a 392 steroid, my .177 I got when I was 9yo, and my father's MSN pistol circa 1945.
When I saw a factory refurbished Marauder at the gun show, the price was so attractive I had to "pull the trigger". It is well used by me and I am fascinated by the ability to tune the internal ballistics and the surprising accuracy even out to 100 yds.

Yesterday, a couple of new vermin rodents decided to have a go at the bird feeders and bird seed cabinet.

First shot on a fresh fill I saw the twig that deflected the pellet. Second shot I was carefully threading the needle through the twigs...when I released the shot, all of the air dumped through the muzzle. Loud, scary, etc. My first though was that I would have to pump from zero...which I had only done once.

With my tune, I shoot 20 heavys at around 900 and then switch to the premiers and get 10 more. 30 shots into same POA with the 30th at about 890 and then I refill from about 1900 to 2900.

Looks like I am going to have to go inside. It would be very nice to get some input as to what parts to have on hand before I open her up as I do not wish to try to remember how it goes back together over the time it takes for parts to arrive. I figure I should replace all of the O-rings, what else? Should I go with stock parts or do an upgrade while I am in there? Is there any way to save my tune settings? Grease or oil?
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Re: Marauder dumped air

Postby Panic Button » Sun Feb 04, 2018 2:10 pm

Rodent Slayer wrote:New member here.
I have been a long time fan of Benjamin products. I have a 392 steroid, my .177 I got when I was 9yo, and my father's MSN pistol circa 1945.
When I saw a factory refurbished Marauder at the gun show, the price was so attractive I had to "pull the trigger". It is well used by me and I am fascinated by the ability to tune the internal ballistics and the surprising accuracy even out to 100 yds.

Yesterday, a couple of new vermin rodents decided to have a go at the bird feeders and bird seed cabinet.

First shot on a fresh fill I saw the twig that deflected the pellet. Second shot I was carefully threading the needle through the twigs...when I released the shot, all of the air dumped through the muzzle. Loud, scary, etc. My first though was that I would have to pump from zero...which I had only done once.

With my tune, I shoot 20 heavys at around 900 and then switch to the premiers and get 10 more. 30 shots into same POA with the 30th at about 890 and then I refill from about 1900 to 2900.

Looks like I am going to have to go inside. It would be very nice to get some input as to what parts to have on hand before I open her up as I do not wish to try to remember how it goes back together over the time it takes for parts to arrive. I figure I should replace all of the O-rings, what else? Should I go with stock parts or do an upgrade while I am in there? Is there any way to save my tune settings? Grease or oil?

I haven't had this happen personally, but I've read about it here. Look at this link
viewtopic.php?f=30&t=12005&p=79158&hilit=dump+air#p79154
that should help get you started in your search for the solution.

Cheers, PB
Benjamin Marauder, Gen-2, Synrod, .22cal
ATN X Sight 2 HD 3x14 scope
80 cu ft scuba tank w/gauged fill hose
Yong Heng 4,500psi compressor
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Re: Marauder dumped air

Postby 22synrodn » Sun Feb 04, 2018 6:31 pm

Sounds like the poppet inside the valve cracked on you which is not uncommon after some aging. Really, to keep it simple, all you really need is 5 #118 o-rings and another poppet along with some silicon grease to lube the o-rings. It is a very simple fix, and you are already degassed. I would recommend a few extra o-rings being your first rebuild as you could easily cut one getting it past the gauge port hole if not careful.

I would also recommend ordering some breech o-rings (end of barrel o-ring) and a new set of transfer port o-rings. You can place one order from Crosman for all and be done.

You should be able to keep your same tune as long as you don't turn any adjustments while rebuilding.

There are YT videos of breaking down the gun to acquaint you with this simple process or we can help you more too.
Romans 8:1-11

22 Synrod Unregulated. Tuned using JSB 18.13gr:
30 Shots @ 31.02 FPE Avg., ES 1.36% (12 FPS), 1.58 FPE/CI


25 Synrod Regulated. Tuned using JSB MKIIs 33.95gr:
24 Shots @ 55.92 FPE Avg., ES 2.08% (18 FPS), 1.45 FPE/CI
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Re: Marauder dumped air

Postby Rodent Slayer » Mon Feb 05, 2018 8:28 am

Thanks for the replies.

I should have clarified that the rifle does not pump. Hammer cocked, dry firing several times, and the air from each stroke of the pump leaves without resistance or delay. It does not act like I would presume debris in the valve would act. I think 22synrodn is correct about the busted valve.

I presume that I will be running into the rust dust in the reservoir tube. Can I put a light coat of sil grease inside the tube to prevent that? I figure to grease it and then wipe it all off. The grease that is left should be a barrier between condensation and steel.

Does anybody sell a complete rebuild kit?

I am a pretty fair firearm armorer but do not have experience inside air guns.
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Re: Marauder dumped air

Postby int3man » Sun Feb 11, 2018 8:45 pm

Just as the man said 5 (Buy 12 as Spares are good) O-Rings and a Poppet from Crosman and you should be good to go. Watch a couple of You tube video's and find the one you like. It is pretty straight forward, and the good new is the air is out of the air tube. By a 3/4 dowel at Ace or Hardware store to assist in disassembly and reassembly. I use a Long 1/2 extension. Just watch the O-Rings past the Gauge port as it goes back together. I use my naile file on my swiss army knife to keep them from getting cut.

If you have a fellow memeber near buy they cna help you. Also you may want to Berry hone the Hammer area while it is apart. Hone and deburr all internal edges.

Michael :- )
.25 Marauder Full W.A.R.
PRod Modified Valve, LW Barrel W.A.R. NBH
Broadening my Horizons
.22 Brocock S6 XL
.25 BSA Scorpion Huma REG
.25 Air Arms Extra FAC
.22 Marauder Regulated LW Barrel Rapid 70 Bull Stolen
W.A.R. .30 FLEX DA BOMB!! Stolen
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Re: Marauder dumped air

Postby 22synrodn » Tue Feb 13, 2018 10:01 am

There are a few places you can get the needed O-rings to rebuild your gun other than Crosman.

eBay kit (expensive):

https://www.ebay.com/itm/Crosman-Benjam ... SwCmNZypO2

McMaster-Carr:

(McMaster Carr) O-ring - Gauge Adapter to Gauge Port (X1)
(McMaster Carr) O-ring - Gauge Port (X2), Valve (X1) and Fill Adapter (X1)

The O-Ring store:

(The O-Ring Store) O-ring - Gauge Adapter to Gauge Port (X1)
(The O-Ring Store) O-ring - Gauge Port (X2), Valve (X1) and Fill Adapter (X1)

Breech or barrel O-ring:

For the .22 cal barrel O-ring you can pick up the Danco #47 (11/32" O.D. x 7/32" I.D. x1/16") at HD or other hardware stores. It's the same one that you would get from Crosman, but much cheaper. The Crosman P/N is 1761A023 for .22 caliber. The size is 009.

Some rebuild video links:

Marauder Rebuild Instructions 01
Marauder Rebuild Instructions 02

O-ring replacement video:

How and why to Lubricate an O-Ring

As far as lubing the inside of the air tube, I do this. I have a 3/4" wood dowel and put a wrag (Cut piece of old T-shirt) over the end and spin it through dry or with silicon oil. Then I use a new wrag and put some silicon grease on it and spin it through the air tube. I never see any rust in my air tubes and it makes the O-rings slide well, but they are lubed too. the 3/4" wood dowel is great for pushing the parts in/out too.
Romans 8:1-11

22 Synrod Unregulated. Tuned using JSB 18.13gr:
30 Shots @ 31.02 FPE Avg., ES 1.36% (12 FPS), 1.58 FPE/CI


25 Synrod Regulated. Tuned using JSB MKIIs 33.95gr:
24 Shots @ 55.92 FPE Avg., ES 2.08% (18 FPS), 1.45 FPE/CI
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