Thursday, February 27, 2014

Benjamin Marauder Tear Down

I've been watching the Marauder's on-board gauge drop slowly over the course of the last two months.   It was filled to 3k and now it's down to just under 1800 psi.  I was finally suitably annoyed with the gun and found a free evening.















Pulled off the shroud and removed the action from the stock.  Click here if you need shroud/baffle removal tips.



















This is a "degassing tool".  It is your friend.






















It screws in and presses against the valve stem exhausting the high pressure air.




















Don't just trust that the air tube is empty because a gauge reads zero.  I dry fired the gun until it was empty, then used the degassing tool to double check.  Opening a pressure vessel containing a few hundred psi would be a nasty surprise.  Opening a pressure vessel with 3k in it could be life altering.





















Unscrewed the fill plug.  Little bit of corrosion on the threads.




















Unscrewed the air gauge.
























Removed the bolt.























Don't lose the spacer.
























Reinstalled to keep track of the parts.




































This spring loaded detent bears against and acts as a hold open for the bolt.





















Three bolts hold the breech to the air tube.  Two up front.





















And one in the back.


























































Off with the end cap.

















Remove the allen bolt from the top of the hammer (striker).






















Striker (hammer) removed.  Again, the bolt was threaded back in so I don't lose it.





















Pulled the transfer port seal.  Looks like the same seal as the 22XX CO2 guns use.




















Removed the three allen bolts securing the valve body in the air tube.



















Pushed out the valve and air gauge bodies with a wooden dowel rod.



















O-ring on the front of the valve body is damaged.
















Valve disassembled.






 















A spot of discoloration from the base of the spring.  No big deal.  Polished it out.






















Valve face is pristine.  Not a trace of corrosion.




















Rebuilt the valve with a thin smear of silicone grease.  Got this from a local dive shop.  Not to be confused with a local dive. 



















Here's that damaged o-ring from above.  The o-ring from the valve body looks rolled over in one spot.   This is probably responsible for the air leak.





















Replaced the o-rings.  I believe they're #118's.























Removed the gauge from the stand off and PTFE taped the threads.





















Reinstalled.  Looks aligned with the air tube.




















Air valve installed.






































Threads cleaned up.



















And tightened.  At this point, the air tube is now sealed at each end and can be pressurized.  Filled it to 1000 psi and set it aside for a couple days.




















Since it was still holding pressure later in the week, I finished putting it all back together.  

Update:  After completing the reassembly, I filled the gun to 2600 psi where it has remained for the  last two weeks.  I feel pretty confident that it's fixed.

Thanks for checking in.

4 comments:

Unknown said...

Thanks very much for taking the time to photograph your disassembly. Very helpful.

Anonymous said...

My pump will not fill my marauder. Seems like no air is going into gun no matter how long I pump.

Keith Jurena said...

Ah, dreaded condensate issues. I ended this problem by feeding the pump dried air from a small air tank that has a pound of desiccant in it. The air pressure is reduced to 20 psi before it enters the Benji pump. This also supercharges the pump meaning fewer strokes with only slight increase in effort.

Keith Jurena said...

The desiccant of my choice is 4a molecular sieves in 2 mm spherical size. These dry air to a dewpoint of -40 which is identical to SCUBA air and is what SCUBA air filter packs use. By filling my dryer tank with air from a shop compressor at 120 PSI, I have already removed 90% of the water so recharging the desiccant is a once a year task.

Before I used this system, I had to overhaul the pump every month and that was only 500 shots or so. That was four years ago. I have since moved to a location where air rifles are more friendly and shoot a bit more.