Hi all,
After buying a decidedly underpowered Hw90, I decided to strip it down, replace the seals and valve, and re-assemble. Everything went well, pumped it up (to 10 bar), only to find that I couldn't cock it. Thinking that I had overfilled it, I tried to let some air out, only for ALL the air to escape. Filled to 5 bar, rifle would cock, but when fired, all the air would escape. Filled again to 10 bar, same issue. Am I missing something here? Feels like I've done something wrong, although I do find it odd that when trying to let some air out, the valve stays open and it all leaves....
Pity you decided to re-seal it. If you had just topped up the ram pressure it would have probably been fine. They do tend to leak over years, I have topped up a few in the last few months. Firing should not release any air from the sealed unit, the seals or valve must leaking again somehow.
Baz
BE AN INDEPENDENT THINKER, DON'T FOLLOW THE CROWD
they say a sharp tap in the theoben and hw90 pump instructions not sure why it wont cock though. there is lots of answers about how much pressure it should be .
i have never had mine stripped . what pump are you using to pump it up? could the pump be inaccurate ?
i topped mu evolution up and chronoed it .i have the slim jim pump with no gauge on it .
It is hard to read the pressure on the gauge as it is so low. When I have topped rifles up it seems to read about 350 p.s.i. On a .22 I normally have to tap the valve lightly to release a little pressure to get 11.4 ft.lb. A tiny release or air pressure can make a huge difference in power on the HW 90.
bAZ
BE AN INDEPENDENT THINKER, DON'T FOLLOW THE CROWD
Hi,
One of my old Theoben Beeman/HW 90s was cocking intermittently. The problem turned out to be serious wear through the pin at the front pivot point and also wear in the hole through which the pin fits. I had to replace the whole cocking lever and pin. Essentially I could not move the cylinder far enough rearwards to engage and cock the rifle. Now all is well.
Jim
via Ballarat
Australia
some people are using suspension shock pumps from mountain bikes
https://www.tredz.co.uk/.RockShox-Hi...0aAlDWEALw_wcB
so unless its a top end branded one the gauge may read wrong.
if using a pcp tank to fill i dare say it would be hard to stop it blowing a seal if you let too much air rush in . having never used a pcp tank to pump one up i may be wrong. using a hills type pcp pump would be safer for me anyway.
according to a post on here in 2006 the hw90 needs to be pumped up to 17bar . which is around 260 psi
http://www.airgunbbs.com/showthread....-gas-ram/page2
but i have heard loads of different pressures being mentioned .
Last edited by bighit; 30-09-2017 at 09:52 PM.
Thanks for all your input guys, it's much appreciated.
The pump I've been using is a Bay special, which has worked fine with my HPA XS79, although with that I've always gone by the gauge on the bottle and not on the pump. Maybe you're right about the gauge being messed up. I'll give it another go tomorrow I think.
Make sure the cocking arm is in the correct spot in the piston and then you have to Re set the safety catch before you replace the trigger guard
Ive just done mine
Last edited by 10/10; 01-10-2017 at 04:30 AM.
The initial pressure you pump to is not critical as long as it is not too high to cock the rifle or damage the seals. It is very unlikely you are going to get exactly the power level you want without tapping the valve to release a bit of air. If you put too much in at your first try the 90 will be almost impossible to cock. I use a Hills pump.
Baz
BE AN INDEPENDENT THINKER, DON'T FOLLOW THE CROWD
Given it another go, and still no joy. I think that this one is beyond my abilities, and I don't want to mess it up anymore. Just have to decide if I want to sell it as spares or repair, or break it up for parts. I've got too many others that need work on, work which I'm capable of and have done before, so I think I might just cut my losses on this one. If anyone's interested, let me know.
Never taken mine apart - Question - is any of the dynamic sealing O-ring based? If so - O ring sizing can be critical. Similarly, it is easy to damage an O ring when being fitted. End of the day, the leak is seal related so a very close inspection ought to reveal the problem, assuming they were correctly sized.
**WANTED**: WEBLEY PATRIOT MUZZLE END; Any Diana/Original mod.50 parts, especially OPEN SIGHTS
Yes Karl, the main ram seal is an o- ring, and yes, sizing is critical. Nb it also has a delrin backer.
Always looking for any cheap, interesting, knackered "project" guns. Thanks, JB.