Tinker at your own peril. This post is not intended as the last word on HW100 setup/tuning. I do not claim that terms and info are 100% accurate but are here simply for you to relate to:-
HW100. Great rifle, lots of little niggles, easily fixed IME. I'm going to assume you have seen the various stripdown guides on the web and are fairly competent at dismantling your rifle, so let's dive straight in:-The main culprit:
The breech block ("valve cap" on HW diagram) is sealed with a large 12x1.2 O-ring. HW have opted for a crush installation
. The O-ring is pinched between breech block and action acting like a gasket seal. However, this prevents the two parts from mating properly and also allows some movement, perhaps only a couple of thou but it's enough to cause problems, i.e. loose barrels (made worse by excess oil) sticking magazines and slow leaks. The O-ring is effectively destroyed upon assembly. Herr Weihrauch IIRC made a comment regarding an O-ring that always needs replacing during a strip/service, he didn't say which, but I think it's this one. Simply replacing this O-ring with a 12x1 and degreasing front half of action including barrel and grubscrew (there's a lot of oil in this area) along with careful reassembly and you'll never suffer any of these issues again.
Here's a pic of the damaged factory O-ring
With the valve cap/breech block removed it's worthwhile making a quick inspection of the following:-
1. Check valve seat for damage. Any scratches can be removed by catching a wad of Scotchbrite (grey/fine) or 000-0000 steel wool in the chuck of a twist drill and applying with light pressure
to the valve seat. Valve can also be cleaned by catching the base in a drill and applying wad of abrasive by hand. Be very gentle and try not to change the angle of beveled edge/sealing face. Only perform this operation if the valve has scratches or debris embedded in its surface. Clean with paper towel, lint free cloth or use a blast of air from your tank.
2. Valve return spring has closed and ground ends which can be quite rough. If you like you can polish with 1200 grit wet/dry.
Make sure all above components are absolutely clean and dry before replacing.
3. Inside the breech block are two O-rings which seal the valve stem and pellet probe/bolt. These will only leak during firing cycle and are not responsible for any slow leaks or loss of pressure (sizes listed below). A good tip for fitting the probe O-ring is to push a cleaning pellet up to the groove and maneuver the O-ring into place from opposite side.
The new main seal 12x1 sits nicely in its groove and deforms under air pressure to seal, as an O-ring should. Sometimes the replacement 12x1 will fail to seal, if so choose a new o-ring. Try to eyeball one that looks a little thicker, there is some +/- tolerance on both c/s and I/D. The 1mm c/s is right on the lower limit it seems. This is probably why the factory use a 12x1.2. On the production line this o-ring needs to seal first time every time.
Ensure securing bolts are free of any excess oil and clean threads with a brass brush, the breech block can now be properly secured and the main seal O-ring can even be reused should you strip the rifle in future.
The barrel is held against the breech block and action in a wedge type arrangement, once clean and properly fitted it holds very well. There's no need for additional securing via extra screws but I wouldn't recommend against them, it's your choice. Clean all oil from barrel, barrel channel and grub screw. Make sure grubscrew is dry and threads are clean. The barrel can now be secured in position - use short end of Allen key to finger tighten - barrel will not loosen until you want it to. Do not use too much force when fitting silencer, it seems the loose barrel issue worsened with the introduction of the screwcut MKII and heavy handedness when fitting silencer is partly responsible. Pro-tip:- Keep silencer on gun, you are not James Bond.
(Note: there is a trade off here, having barrel and various securing bolts dry increases risk of corrosion. An occasional visual inspection is recommended)
If after securing valve cap you find the firing valve leaks (rapid air loss through barrel channel) and you're sure that there are no scratches/debris in valve/valve seat surfaces and that the valve spring is correctly positioned in its recess then this can often be fixed by lapping the valve onto the valve seat. Sometimes a firing valve is simply fussy and may need a few attempts to seat and seal, it's worth removing the valve cap and refitting a few times before resorting to the lapping method. This maybe due to some sort of asymmetry leading to the valve wearing on one side. If you persevere you may finally get the valve to seal, though I have given up on some rifles and ordered a new valve. The new valve always seals suggesting wear is to the valve only and not the valve seat.
To lap the valve/seat - Catch the valve (plastic tail of valve that fits inside valve spring) in a drill, be gentle when tightening drill chuck or protect the valve with tape. Seat the valve in the valve cap and spin for a few seconds whilst applying light pressure
. Put away the toothpaste as no lapping compound is needed IME. Inconsistent power:
The heavy grease HW use on the hammer doesn't help RE: varying power. Consider that most PCP's run with a dry hammer. This grease is dissipated through use, may be thinned if a lighter oil is introduced or changes in temperature can affect its viscosity. All affect the force with which the hammer strikes the firing valve. Degrease and lube the hammer and shuttle with a thin oil. As it's steel on alloy, do not let the hammer run dry. Wet periodically with a drip of oil through the trigger slot. I'd also recommend cleaning up both hammer/shuttle to remove rough edges. Chuck 'em up in hand drill and give it a quick spin applying light pressure
with 1200grit wet/dry. The hammer has a single circular bearing surface just in front of the rear spring guide/pip. You don't need to mirror polish either part.
Onto the main valve; removed from the action with a deep 10mm socket, this valve consists of five components. Two threaded brass parts that make up the valve body and inside, a 4mm ball bearing (regulating valve) a spring and an O-ring. This O-ring is used to seal the two halves of the valve body. This O-ring doesn't appear on any parts diagrams/lists, size is 2x2. IMO this is to large in cross section and is pinched between the two halves of reg valve body reducing ID further. This reduced ID can interfere with the consistent seating of BB reg valve (if you look closely there appears to be a profiled seat cut into the main valve body). I think that over time this O-ring takes a set and hardens after which it probably forms a fairly reliable valve seat but sometimes not. This gradual hardening may affect reg output pressure and along with hammer grease cause power to drift. Simply replace the factory O-ring with a 2.57x1.78 (#005) Ensure BB is free from debris and grease/moisture from fingers before reassembling the valve. The O-ring is probably best fitted dry. The valve only needs to be fitted finger tight and just nipped up when replacing in the action. Igor Jelenski -who first suggested this O-ring swap recommends trying a 3mm BB and a stronger spring. The idea is the 3mm BB clears the O-ring ID to form a much more reliable and consistent seal against the valve body. If you'd like to experiment with this I would also suggest sleeving the spring retaining portion of main valve with some 1/2mm PTFE sheet to keep BB centralized. Looking closer I can't guarantee that the factory 4mm BB does indeed clear the #005 O-ring ID to seal but it's a matter of minutes to swap out the main valve components and I therefore recommend everyone should also give the 3mm BB a try.
Over time the reg piston O-ring will take a compression set becoming somewhat square in cross section, as this is a dynamic seal this can result in leaks and erratic performance. Simple to replace, size is 7x1.5 same as main valve outlet.Fine tuning:
You can make your own reg output tester quite easily using 1/8 BSPP female - 6x1 male tapered adapter. My gauge is from MDE and is 1/8 BSPP back entry. If tapered the male thread on the adapter is self sealing (if this isn't the case use some PTFE tape on threads) Drop an O-ring 5.28 x 1.78 (#009) into adapter before fitting gauge, it should seal finger tight . Adapter is available from "thenippleshop"
Clean before using, you may also need to shorten the male threaded section.
To use pressure tester you'll need to remove BB from test port under grubscrew. If stuck it can be pushed through from inside with a small Allen key (remove reg valve and piston to access and be careful not to scratch action) Sometimes there is some kind of seal under the BB. It's hard to tell if this is an O-ring as it's usually completely destroyed. Bits of this seal could find their way into the regulator. I'd recommend removing altogether as it's not needed to seal the port, just tighten the BB down onto it's seat which is cut into the relatively soft alloy action, it should seal perfectly well.
Belleville washers that control reg output can be quite dirty and may benefit from a clean and very light lube, just wet between fingers with a light oil. Stack as follows (())(())(())(())
The factory setting for the regulator output is approx 90BAR +/- 5BAR
The reg settings vary from rifle to rifle. Longer barrels and larger calibres tend to use a lower reg setting(85-90BAR) and smaller calibres/shorter barrels a higher setting(90-95BAR) Actions I receive for service/setup show reg output pressure that vary from 60BAR all the way up to the reg permanently open exposing the firing valve to tank pressure(200BAR!)
A slightly higher regulated pressure coupled with less hammer spring tension can increase shot count (lot's of testing and patience required here) as valve duration is reduced as are the effects of hammer bounce. The increase is subtle, but off reg velocity spikes can be avoided. Otherwise use an 85BAR setting for .22 rifles, 90 BAR for .22 karbines and .177 rifles and finally 95BAR for .177 Karbines. If you don't have a pressure tester make a note of reg spring tension adjuster position before dismantling. Mark 12 o'clock position on the screw (Tippex or WHY) and count the turns to remove. Alternately, accurately measure depth of adjuster screw relative to action before removing.Finally:
It's worth noting if your gun loses pressure when stored and you're unsure of the source of the air loss, all slow leaks on the action can be fixed with 5 O-rings in just 3 sizes.
12x1 Breech block (once fitted it's unlikely this will leak again) x1
7x1.5 Reg piston and main valve outlet x2
2.57x1.78 (#005) main valve inlet and internal x2
The #005 O-ring on main valve inlet wears quickly and should be changed regularly as it can start to disintegrate whilst still sealing and bits of this seal may find their way into the action. A Polyurethane O-ring (PUR70) is recommended here but not essential, they are quite expensive and difficult to purchase in small quantities.
When speaking of slow leaks on the action I specifically mean leaks due to O-ring failure i.e not firing valve leaks. Also, the rifles seem to go through continuous incremental changes and I can't be certain that O-ring sizes and recommended alternatives are always suitable. If after changing the above O-rings you're still puzzled by leaks you can drip a thin oil onto the action and around various seal faces and possible leak paths to identify or you may be loosing air via the reg test port or the firing valve/valve seat interface, both of which are covered above.
Use pure Silicone grease on all O-rings except Main valve internal
Tip: When removing old O-rings push a pin into the O-ring itself or use a new razor blade and be careful, don't try and dig under the seal as you may scratch the sealing surfaces.
Here's the full list of factory O-rings and some recommended alternatives (bolded) All O-rings are NBR 70 unless otherwise stated.
O-ring HW 100, 37.1 x 1.6 Cylinder clamp 2682C
O-ring HW 100, 15.6 x 2.5 Barrel clamp 2682B
O-ring HW 100, 32 x 2.5 (or BS#124) Magazine 2603A*
O-ring HW 100, 13 x 2 Adaptor A 2704
O-ring HW 100, 2.57 x 1.78 Adaptor B 2703B
O-ring HW 100, 3 x 1.5 (PTFE) Valve stem 2655D
O-ring HW 100, 12 x 1.2 Breech block main (12 x 1) recommended
O-ring HW 100, 5.5 x 1 Breech/probe seal .22 2659A*
O-ring HW 100, 4.5 x 1 Breech/probe seal .177 2659A*
O-ring HW 100, 4 x 1.5 Probe buffer 2618A*
O-ring HW 100, 2.57 x 1.78 (PUR70) recommended
Main valve inlet 2665D
O-ring HW 100, 7 x 1.5 Main valve outlet 2666
O-ring HW 100, 2 x 2 Main valve internal (2.57 x 1.78) recommended
O-ring HW 100, 7 x 1.5 Regulator piston 2668
O-ring HW 100, 10 x 1.5 Tension adjuster (sometimes omitted) 2672
O-ring HW 100, 8 x 1.5 Barrel 2679
FX/V-Mach Probe, 5.28x1.78 PUR70
Don't waste money on others "seal kits" Source them yourself, you can buy a lifetimes supply for £10 - £15. Try your local hydraulics shop for the common imperial sizes #005 + #009 or look online.
Be aware, there is nothing to be gained from using harder O-rings than the std 70shore, in fact if O-rings are too hard they may not deform sufficiently to seal. Don't be tempted to order your O-rings in the exotic sounding VITON material. NBR O-rings have greater tensile strength, higher elasticity and better resistance to brittleness at low temperatures than VITON.
One final tip for assembly: Ensure hammer clears the top sear before you tighten bolts securing the trigger mechanism. You'll crack/chip the middle sear if not done correctly.