Mares Minimini Sten Air Leak Help

[NateKirby]

I was just given a Mares Mininini Sten that is leaking air. I took it all apart, cleaned it, lubed, and reassembled. It is still slow leaking around the nose cone/muzzle. I plan to change the O ring on the plastic piston. Anyone know if I'm supposed to put anything on the threads of the nose cone before tightening to help make a seal? Any other advice? The air is seen leaking out of the vent holes in the cone.
Thanks so much for any input!

 

[popgun pete]

You need to change the "O" ring that sits on the inner barrel that presses against the rear of the nose cone. Put some grease on the end threads when you slide the "O" ring over them to prevent any scratching of the "O" ring by the thread peaks. You should also change the piston seals. You can buy a kit that has the necessary rings and seals. Do the job right and you only have to do it once so I suggest you replace all of the seals.

Mares pneumatic speargun Sten / Jet Service O-RING kit | eBay

Pneumatic spear guns need to be serviced regularly to ensure that they are in correct working order. The Mares o-ring kit is for use when servicing Sten and Jet Pneumatic Spear gun. We also have a high-standard team, qualified by authorized organizations to ensure products are of the highest...

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[NateKirby]

You need to change the "O" ring that sits on the inner barrel that presses against the rear of the nose cone. Put some grease on the end threads when you slide the "O" ring over them to prevent any scratching of the "O" ring by the thread peaks. You should also change the piston seals. You can buy a kit that has the necessary rings and seals. Do the job right and you only have to do it once so I suggest you replace all of the seals.

Mares pneumatic speargun Sten / Jet Service O-RING kit | eBay

Pneumatic spear guns need to be serviced regularly to ensure that they are in correct working order. The Mares o-ring kit is for use when servicing Sten and Jet Pneumatic Spear gun. We also have a high-standard team, qualified by authorized organizations to ensure products are of the highest...

www.ebay.com

Wow, thanks so much for the insight! I really appreciate you taking the time to help me out. I changed the O ring on the piston and that seemed to help a bit. I'll do as you said and change the one on the barrel for now until I can order the full kit.
If I can ask 2 more questions, what type of oil should I put in the gun, and how much on this little Sten? It is the 16 inch minimini gun.
Thanks so much!

 

[popgun pete]

Fork oil for motorcycle suspensions is ideal, the SAE 10 grade. Autospares shops have it, you can buy it anywhere in small plastic squeeze bottles.

Note the 58 cm gun is the Ministen, this table was in a Mares Service document and the Miniministen is only the 42 cm gun, not the 58 cm. Someone goofed typing the table.

 

[NateKirby]

Fork oil for motorcycle suspensions is ideal, the SAE 10 grade. Autospares shops have it, you can buy it anywhere in small plastic squeeze bottles.
View attachment 57486

Note the 58 cm gun is the Ministen, this table was in a Mares Service document and the Miniministen is only the 42 cm gun, not the 58 cm. Someone goofed typing the table.

Thanks so much for this info! I found a manual with the air pressure, but it didn't have the oil quantity. I truly appreciate your help! Have a great day!