Steyr LP10 Suddenly Died...

[Gwhite]

We were running a practice Final for the college pistol team I help coach, and our top shooter's LP10 started dropping shots well below the target. The sound of the shots was much too quiet. My first guess was low pressure, but the cylinder gauge read around 110 Bar. I popped it off and put it on our fill tank, which has a large high quality gauge, and the pressure was pretty much spot on. I filled it to about 190 bar, and the pistol still wouldn't shoot right.

I checked to see if any of the seals had disintegrated, and they all look OK. Either the pressure isn't right coming out of the regulator, the firing valve isn't opening fully, or there is a serious leak someplace past the firing valve. I have a spare regulator I can install tomorrow to narrow things down.

I was wondering if anyone has encountered this before. Do the striker springs ever break? We have a half dozen LP10's, and a couple LP1's that were converted to PCP, and we've never had one go bad this abruptly. If swapping out the regulator doesn't work and I can't find a seal that has let go, I will probably send it off to Pilkington.

Thanks!

[hohungyi]

Before you swap out the regulator, do check if it’s just a case of turning the regulator adjustment screw.

Open up the two hole screw where the regulator normally contacts the cylinder pin, and inside you’ll see a small silver screw, turn that clockwise until you hit the end, then turn it counter clockwise 1/4 turn. Put everything back together and see if it helps!

I just had this happen to me a couple months back, was fiddling around with my LP10 and this worked for me.

Good luck!

[rmca]

This is how I would try to fix it:
1- Check if the o-ring on the bottom of the bolt is still there.
2- Check if the o-ring on the inside of the bolt face is still there.
Any other o-ring failing would cause an air leak, so I would rule those out.
Next, probably something came loose or broke.
3- Check the velocity adjustment screw to see if it's loose.
4- If it's thigh, remove it and check the spring for damage.
If nothing helped, then the problem is in the valve or the regulator.
5- Remove the regulator (without opening it), and check the valve and it's housing for damage or debris.
6- Last, the regulator. Either it's internal o-rings or the springs (washers) are bad.

Hope this helps

[Gwhite]

Thanks for the responses! Another forum member PM'd me and said his pistol had the same sort of failure. His regulator valve had gotten gunked up (bad/moist air?), and he had to clean it. After that, it was fine.

Both the green O-rings in the breech mechanism are there. The bigger one the bottom of the bolt seals against looked fine, and the one inside the bolt face was there, but I didn't have time to make sure it was intact.

I'll have more time to examine & experiment this evening. I found this diagram on-line for an LG-100 regulator, which I think is the same design as in the LP-10, only they change the Belleville spring arrangement to get a different pressure value:



It looks like the regulator valve seal is a small disk. I'm not sure where one can get replacements if that is damaged, but that is unlikely.

There are also YouTube videos on disassembly & cleaning:

https://www.youtube.com/watch?v=0jyaUiHClm0

and removing the firing valve:

https://www.youtube.com/watch?v=anZalW2f_aI

I'll report back on what I find.

If I end up rebuilding regulators more in the future, I may want to invest in a regulator test gauge. Steyr sells one, but there are also plans & videos on how to build one.

[hohungyi]

Euroshooting sells the regulator gauge :)

https://www.euroshooting.eu/en/index.ph ... 4002080523

[Gwhite]

Thanks! I was going nuts trying to find one for sale. Now that I have the part number, this place has them considerably cheaper:

https://www.benke-sport.de/steyr-druckm ... d-lp-36991

That price includes VAT. Without that, it works out to ~ $127 USD, which isn't too bad. It’s not clear if they ship to the USA & how much that might cost.

[brent375hh]

Very possible that switching out just the two o-rings on the regulator piston will fix your problem. The big one is a dash 904. The o-ring on the inlet valve either seals or doesn't, so that is not your issue. Make sure your washers get stacked as they were. One of mine came ()()()(), the other.was (())(()). I changed them both to the latter configuration, that seems more consistent. The inlet screw can also be adjusted wrong, but not likely if it hasn't been touched. I don't have a gauge but just used a cylinder with 60 bar and one with 200. Adjusted the inlet screw until I got the same velocity out of both. About 3/4 turn.

If you remove the set screw for the striker spring velocity screw, it can all slide out the rear.of the frame by lifting the cocking handle.

Still most likely the piston o rings...

[rmca]

I don't recall were I got this pdf with some more info on Styer regulators.

Regulator Info Steyr 2016.pdf

(39.66 KiB) Downloaded 334 times

Maybe here...
Anyway, should help.

[Gwhite]

Thanks! I went to save it, and found I already have a copy...

[hohungyi]

Thanks! I was going nuts trying to find one for sale. Now that I have the part number, this place has them considerably cheaper:

https://www.benke-sport.de/steyr-druckm ... d-lp-36991

That price includes VAT. Without that, it works out to ~ $127 USD, which isn't too bad. It’s not clear if they ship to the USA & how much that might cost.

Oh I initially tried to buy one off these guys, but after a couple days of email communications, it turns out they couldn’t send it to me in Singapore.

Would be good to drop them an email to check if they are able to ship into the USA!

[Gwhite]

Update: Last evening, I examined the pistol, and nothing was obviously wrong. I did notice that the cylinder valve only opened with very little gap between the cylinder and the frame. It may be that the cylinder valve wasn’t opened fully. I put a different cylinder on it, and it appeared to work OK. The two bolt O-rings looked a bit mashed, and I decided to replace them with some Viton ones we have. That appeared to work OK, except I had to adjust the barrel slightly tighter to get the cocking lever to stay down.

I gave it back to the student, and it was shooting about 3 inches higher. That seemed odd, but that could be from fixing leakage at the breech seals, although that seemed like a very big elevation difference. He re-zeroed, and shot a nice group. He took a break, and it was suddenly shooting very low. From there, it wandered up and down almost the full height of the target. It would shoot fine for a bit, and then suddenly change elevation. I had to attend a meeting, and only got most of this second hand after the fact.

I suspect that the regulator has lost its marbles, but I didn’t have time to go back and try swapping in our spare. It's either that, or somehow the barrel worked loose after I adjusted it. I will try again on Thursday...

[rmca]

I suspect that the regulator has lost its marbles, but I didn’t have time to go back and try swapping in our spare. It's either that, or somehow the barrel worked loose after I adjusted it. I will try again on Thursday...

That is how I would proceed.
Three inches is a lot for the problem being the breech o-rings.
My money is on the regulator's internal o-rings giving up.
It has two o-rings inside that are a strange size for metric, a 8.92x1.83 and a 2,9x1,8.
Perhaps they translate to imperial better.

[Gwhite]

Information I have is that they are:

3 X 1.5mm Durometer 90 for the small one on the high pressure side
Trade size (or "dash") 904 Durometer 70 for the one on the low pressure side. This is a US standard O-ring size.

I'm surprised at the discrepancy in the size called out for the small one. I had an LP-10 rebuilt several years ago by our host, and among the parts they replace is an O-ring listed as 3 X 1.5mm, part #4002090018. I'm guessing that is a Steyr part number, but I've never found a diagram or parts list that shows the internals of the regulator.

Further digging came up with this page:

https://www.euroshooting.eu/en/index.ph ... 4002090018

In addition to being used in the regulator, it looks like that O-ring is also the one that is cut and provides fraction/damping in the stabilizer.

[pbrejsa]

http://www.sskpraha6.cz/docs/Steyr_LP10_draw.pdf

[Gwhite]

Lovely! Thank you!

That's the first drawing I've ever seen that shows the regulator internals. There are actually more parts than I expected, like the # 29.6 "Guiding sleeve".

[pbrejsa]

Small particles of the o-ring 29.9 (4 x 1,5 mm) penetrate into the interior of the pressure reducing valve 29 and prevent its proper functioning. This is the most common cause of the mentioned problems. It is very important to visually check the condition of the o-ring 29.9 regularly and replace it at the slightest damage. The o-ring 29.9 must be at least 90 Shore hard. High hardness is very important. The original (polyurethane or FPM, who knows?) will last 2 to 4 years with proper care and maintenance. The NBR90 ring needs to be changed at least once a year. The ring is most easily damaged when loosening and sensing the air container at full pressure (200 to 100 bar). Even if it's completely unnecessary.
You must be careful when removing the 4 screws of the reduction valve and when installing a new or repaired one. The threaded holes in the gun body are often cracked due to stress corrosion cracking and the low transverse strength of the extruded material (probably a combination of exfoliation corrosion and stress corrosion cracking). Cracks can then be a source of air leakage and other problems. After many years of use, these cracks may be hidden under the outer layer of the surface finishing and only be discovered when the next pressure reducing valve is installed.

[Gwhite]

I worked on the LP10 that was acting up, starting by checking the velocity. I didn't see anything that would explain the +/- several inch elevation swings, but the velocity was quite low (around 147 m/sec, versus the recommended 155 to 160 m/sec. However, in 10 shots, I saw the velocity vary by about +/- 3 m/sec which is much more than I think it should be.

I replaced the regulator with our spare. In the process, I discovered that the firing valve seal was different from the spare we have:

I wasn't absolutely sure if they had changed anything else internal to work with it, so I left the old one in place. Is the new version a direct replacement for the one with the green O-ring?

I test fired it, and the report sounded very weak. I haven't worked on the velocity adjustment on a Steyr in several years, and should have double checked the video. They instruct you to only loosen the locking screw about 1/8th of a turn. I loosened it a lot more than that, and that artificially reduces the velocity. Once you think you have it about right, when you tighten the locking screw, the velocity goes up a LOT.

Once I figured that out, I got it adjusted to around 159 m/sec and the velocity variation was down to +/- 1 m/sec. I believe the factory tests with heavy pellets, although the test targets don't specify. We shoot 7 grain pellets, so the pistol will shoot a bit faster than "spec".

Right now, our focus is on getting the team ready for the Collegiate National Championships in less than a month. Once that is over, I will tear the old regulator apart and replace the O-rings. I'm also going to assemble a pressure test gauge so I can verify the front screw setting if I need to take that section apart.

Thanks for all the advice & feedback!

[argus]

If you wanted to go down a deep rabbit hole with Steyr regulators there is some great information at https://shooting-the-breeze.com/threads ... ter.41076/ where they have polished the seal on top of the piston to eliminate creep and improve recovery/consistency etc. These regs are from steyr rifles but they are essentially the same as ours. If you search the site there are a number of good threads on steyr regulators, home made testers etc. on there.

While the Steyr experts are gathered here, may I hijack your thread with a question please. I recently put a genuine Steyr service kit through a 15 year old LP10E, all went well with the exception of one o-ring. The o-ring that seals against the bottom of the bolt (#7 6x2mm) which now dislodges itself slightly on every shot. If I forget to push it back down into the seat when loading I can feel the bolt drag against it while closing. The new o-ring is the dark green type, it seems slightly harder than the old lighter green one I removed. What is the trick to keeping this o-ring in place when replacing it please?

[Gwhite]

Even if the O-ring is "new", the green ones are probably polyurethane. This is because that has the best wear resistance. That said, they have a shelf life of 5 years, and (depending on the exact material) can stiffen over time. Once it gets mashed down, it may not be as much of an issue. The normal recommendation is to lubricate all O-rings, but in this case, you might want to clean the lube off where it hits the sides of the hole. Top (especially) & bottom are OK. That may help it stick long enough to settle in.

Also, if you move the barrel to get a good cocking lever feel on the bolt seal, there will be less compression on the breech seal, which could affect how much drag there is across it, and how compressed it is getting.

[rmca]

I wasn't absolutely sure if they had changed anything else internal to work with it, so I left the old one in place. Is the new version a direct replacement for the one with the green O-ring?

No, it's the same part with a different seal.
I've replaced a couple of the old type with the new ones, and had no issues.