BRNO Aeron B98 Repair Advice

[dulcmr-man]

I own a BRNO Aeron B98 5 shot PCP pistol that leaks. Both cylinders hold pressure but when attached to the pistol lose pressure completely overnight. I'd like to send it to someone for repair if possible. Our host does not service this pistol so I'm looking for an alternate repair source. Failing that, I will (reluctantly) try to rebuild it myself. Any recommendations for a repair depot? Any idea what size O-rings are needed for this task?

Thanks in advance for your help.

Dennis

[Gwhite]

I couldn't find an exploded diagram on-line, but I believe the gas firing valve system is related to the design used in the BRNO Tau-7. The magazine advancement system shouldn't be involved in a leak. The one part I'm uncertain about is the PCP pressure regulator design. If that is leaking, it's unknown territory. I would find a diagram and compare it to a Tau-7.

I've repaired/replaced about a half dozen Tau-7 firing seals over the years. The first thing to try is just cleaning the valve area. This is accessed through a large screw at the back of the action under the grip. If you are lucky, a good cleaning & some grease on the seal will fix it. To avoid fibers that could create leaks, it's best to use foam swaps. I use air tool oil on a swab for cleaning, followed by silicone O-ring grease. One thing to watch out for is any dirt/debris that could mar the surface of the plastic firing seal. It that happens, you don't have much choice but to replace the seal. That is do-able, but isn't a simple job. It's not just an O-ring, and it's a press fit in the pistol, making it tricky to remove, and replace.

The thing that tends to do in the Tau-7 seals is age, sometimes accelerated by rust that comes from condensation caused by chilling when the CO2 is released. I don't think normal firing will do it, but if you have a leak or have to vent the pistol, it can get quite cold. I've had more than one where the valve seat was covered with flakes of rust from the CO2 chamber. It's hard to get a good seal that way...

[dulcmr-man]

I couldn't find an exploded diagram on-line, but I believe the gas firing valve system is related to the design used in the BRNO Tau-7. The magazine advancement system shouldn't be involved in a leak. The one part I'm uncertain about is the PCP pressure regulator design. If that is leaking, it's unknown territory. I would find a diagram and compare it to a Tau-7.

Thanks for the input, Mr White. My owner's manual has an exploded view, but it's in Arizona and I'm currently in California. I will try to find a Tau-7 diagram on line to compare. Any suggestions on where to find that?

[Gwhite]

Here's a reasonably good diagram: https://assets.catawiki.nl/assets/2016/ ... 24cd26.jpg

The firing valve is #27, and the valve seat is #28

[lalka686]

These pistols are very easy to work on and O-ring sizes are listed in the owner's manual.
All of the O-rings are 2mm thickness and the best ones are Viton for CO2 application (IMHO) available from McMaster Carr or Grainger.
Part# = Thickness x Outside Diameter
#62 = 2x9 breach
#63 = 2x8 relief
#64 = 2x12 valve
#65 = 2x18 piercer
There should be bag of spare parts with each pistol from factory which includes extra sights and 5 O-rings, 2ea. #65, 2ea. #62 and 1ea. #64.
This could be external leak from the bottom cap. Try to charge it with a CO2 cartridge and see if the piercing cap will keep it sealed instead of the bulk charging cap. Always have the pistol cocked before screwing on CO2 bottle or changing cartridge.

[Gwhite]

The query was about an Aeron B98, which is PCP. No CO2 cartridges, no fill adapter on the pistol. I suspect all the various static seals are O-rings, but the firing seal will be probably be a hard plastic of some sort.

[bgallenbeck]

I have a BRNO B98 5 shot repeater pistol that I am missing parts for. I need a 5 shot magazine and the filler fitting. Does anybody know where I could get them or a mechanical drawing from which I could build them. I have a machine shop at my house and can machine any parts I need with a good technical drawing.

[Bsquareng]

Last spring I was looking for 5-shot cartridges for a B96 (the CO2 version of the B98) and was able to buy 3 from Matt Jackson of Sureshot -airguns in the UK. He also has literature and some parts for Aeron BRNO airguns. Try www.sureshot-airguns.co.uk

[bgallenbeck]

Thanks, I appreciate the help.