Tuning Maximus loosing power with ample pressure

[Kenmc777]

On two occasions my Maximus would barely get to the target (25 meters) after about 10 shots but still has about 1800 psi. I used my degassing tool thinking that I could deplete and pump it back up. It won’t de-gas. But! I removed the tool and was going to just shoot it to remove the air. Lo and behold, it started shooting at full power! Didn’t have another problem for two weeks of shooting almost every day. This weekend it did it again. I used the tool again and again it had full power. Can someone please tell me what is going on, how to fix and why it won’t degass ? 
Thanks! 

 

[KatoKevin454]

you have either something broken in the hammer chamber or an obstruction, I suggest taking the hammer chamber apart and check it for problems, just remove the back plug and all should slide out.

 

[biohazardman]

I would agree an obstruction in the T-port area maybe an o-ring? Or the hammer is sticking on the sear or something.

You need to remove the breech to get things to slide out of the tube. So pull the breech and you can see if it's the T-port if not pull the hammer and spring. Check for proper trigger and sear operation while you have it apart.

You can do this with the gun still charged with air but be careful you don't hit the valve stem by accident or it will give you a charge of air out the T-port.

 

[Kenmc777]

Thanks guys! I need to find a schematic to understand how to remove the breach and understand the parts. I have worked on a lot of firearms but not air arms. I usually follow “if it’s not broke…”. I don’t think there is anything broke since when I put pressure on the hammer (?) with the de-gassing tool it starts shooting with normal pressure/velocity. It seems it is not getting the full amount of air per shot when it messes up but I don’t really understand how that all works. Hopefully it just needs cleaning. Should I also use silicone oil when putting it back together?

 

[John "spysir" Blount]

https://support.crosman.com/hc/en-us/articles/115000846066-BPM77B12FP-Maximus-177-Cal-Owner-s-Manual-EVP



John

 

[Kenmc777]

Thanks! It says the degassing tool is only for the Discovery so no wonder it doesn’t work on the Maximus. The literature that came with the tool when I bought it listed both models.