FX FX Crown MKI loss of power

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aldea6

aldea6

Member
Jan 8, 2018
608
141
Br, Belgium
Hello , I put a 600 mm .30 barrel on my Crown MKI but , despite a power kit installed , I can't get more than 720 Ft/s with JSB 44grs and the reg at 150 bars . I change the settings : reg pressure , hammer weight , factory spring ....nothings works . I swap the barrel to .22 cal ,500mm , same problem max speed with JSB 18grs was no more than 760 Ft/s , whatever the settings . So I suspect something wrong into the block , but I have no idea what to check . The gun doesn't seem to leak , I checked the transfert port wheel and seems ok . If somebody has an idea , he's welcome . Thanks.
 
Just a shot in the dark here as I’m not familiar with the original impacts. I do believe they were designed stock to run a higher reg pressure?? If that is true you very well may not need the power kit at all. Especially to shoot 44.75. Just a thought as everyone wants to dive head first into changing internals for max power. That can be completely counterproductive if you are not utilizing it correctly. Too hard of a strike on the valve can actually cause lower velocity. When you adjust the power wheel down to very low settings do you get a drastic reduction in velocity?
 
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Something to look at ... The valve pin that the hammer is striking may have become flattened and is not going far enough in to open the valve beyond a certain point. I bought a used Crown MkII that had a .30 cal 380mm barrel with the slug power kit. When going to change to a .22 I made the mistake of dry firing it to bleed the plenum. The heavy hammer slamming into the valve with 150bar of pressure behind it so damaged the valve pin and guide that I had to send it back to FX and have the block redrilled to accept a new valve.

To get a good look at things you need to almost completely disassemble the rifle. Sub12Airgunners has a great YouTube on tearing down and rebuilding a Crown.

Cheers,
Greg
 
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NAProf said:
Something to look at ... The valve pin that the hammer is striking may have become flattened and is not going far enough in to open the valve beyond a certain point. I bought a used Crown MkII that had a .30 cal 380mm barrel with the slug power kit. When going to change to a .22 I made the mistake of dry firing it to bleed the plenum. The heavy hammer slamming into the valve with 150bar of pressure behind it so damaged the valve pin and guide that I had to send it back to FX and have the block redrilled to accept a new valve.

To get a good look at things you need to almost completely disassemble the rifle. Sub12Airgunners has a great YouTube on tearing down and rebuilding a Crown.

Cheers,
Greg
Click to expand...
OK , I first will check the valve stem , because I did what you did : dry firing with heavy hammer and power spring . Thanks Greg.
 
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Trucker3573 said:
Just a shot in the dark here as I’m not familiar with the original impacts. I do believe they were designed stock to run a higher reg pressure?? If that is true you very well may not need the power kit at all. Especially to shoot 44.75. Just a thought as everyone wants to dive head first into changing internals for max power. That can be completely counterproductive if you are not utilizing it correctly. Too hard of a strike on the valve can actually cause lower velocity. When you adjust the power wheel down to very low settings do you get a drastic reduction in velocity?
Click to expand...
Yes , speed drops when power wheel is low . You are right about the power kit ; when I bought the gun it was able to shoot 44grs at 850Ft/s from factory settings , so....
 
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