HW40 problem - help please...

[JonRA]

My HW40 has dramtically lost power

Although their is some resistance as I close the gun (probably around a third of what there used to be), now there isn't enough power to move the pellet - there is just a faint sound of escaping air. It went from firing normally to marked decrease in resistance when closing/decrease in power to not even moving a pellet within the space of 4 shots.

Any thoughts on what might be the cause gratefully received

ATB

Jon

[eyebull]

I assume you have been putting the odd drop of oil on the piston to lubricate the o-ring?
If you have and it is still losing pressure then it may be this: The Beeman P17 has a common fault which some HW40s may share - the O-ring on the piston catches on a burr around the inlet hole, and eventually it gets worn enough to lose pressure.

It's an easy fix - loosen the grub screw at the end of the piston where it is attached to the frame, tap the hinge pin out and remove the piston. If you need to replace the O-ring then apparently that size is available from B+Q. Of course chambers also stock it.
Get a bit of very fine wet'n'dry and deburr the inlet hole inside the cylinder, then replace o-ring and piston. You should have no more problems after this.

[peteswright]

Good advice from eyebull. If you can hear air escaping from breach seal end, its probably the valve seals. The piston leak tends to be a gradual one, and tends not to be heard. The repairs are easy to do and I replaced all my seals (3 in all) and can be bought from B&Q. You need "Plumb sure" mixed o'rings 1/16" pack for valve, and Plumb sure 3/32" pack for piston. This will help. my.tbaytel.net/~coopers@tbaytel.net/HW40Review/ My repairs were done on Beeman P17s but its the same gun essentialy.

[JonRA]

Many thanks eyebull and peteswright - that is really helpful - if you or anyone else knows of some pictures or a video showing the strip and reassembly that would be the icing on the cake! (I am not very knowledgeable about the parts..and not too practical once I do know what's what - but without a spring inside to fire bits around the living room, I might just have a go!)

ATB

Jon

[eyebull]

Hi Jon, can't find a link at the moment but I'll take a sequence of pics for you when I get home. Nothing to be scared of with this one, it's pretty straight forward.

[JonRA]

Hi Jon, can't find a link at the moment but I'll take a sequence of pics for you when I get home. Nothing to be scared of with this one, it's pretty straight forward.

That would be brilliant - many thanks eyebull

[peteswright]

http://anotherairgunblog.blogspot.co...ul-finale.html Try this. And this. http://anotherairgunblog.blogspot.co...ul-part-1.html

[eyebull]

/\ Couldn't do any better than that!
LMK if you need any specific pics in greater detail.

[JonRA]

Many thanks Both - this is plenty to go on (though quite daunting - it's even more intricate than I thought!). Don't worry a out any more pics eyebull.

I will see how I get on - or whether I chicken out and talk to an RFD. In order to give myself a chance of doing it myself, I will not rush into anything and try and set aside time and tools to have a go

ATVB

Jon

[eyebull]

Try the piston o-ring first, if that sorts it then you won't necessarily have to strip the whole thing.

[Yammer]

Al you needed to do was scroll down a little. I posted this a few days ago

http://www.airgunbbs.com/showthread....emble-the-HW40

[peteswright]

Many thanks Both - this is plenty to go on (though quite daunting - it's even more intricate than I thought!). Don't worry a out any more pics eyebull.

I will see how I get on - or whether I chicken out and talk to an RFD. In order to give myself a chance of doing it myself, I will not rush into anything and try and set aside time and tools to have a go

ATVB

Jon

AS eyebull says, try piston first (Alan key and punch). Inspect the o'ring. If you can see a notch in it where it sweeps across the inlet hole you can even try moving the notch away from the hole position, this sometimes works. The trickiest part of strip down is taking the trigger and springs out but if you can remember how it goes back everything else is easy. Its worth having a go, you'll learn from it, and have confidence for future repairs.