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More Airmax MK2 tinkering

May 26 2017 at 4:29 PM
Alex in Upstate NY  (Login awilde)
YF12

So after fiddling with the regulator and getting everything too loose the whole gun had seized up on me and wouldn't fire and couldn't crank the regulator back up or anything else so took advantage of the moment to tear the whole thing apart and start doing a little reworking. Some of the interiors were pretty fouled up, several had grits of aluminum dust and most of the orings were drier than a popcorn fart. Also I think whoever assembled my pistol was dyslexic as several things were bass ackwards to what they should have been which was probably why the chrony was jumping up and down 100+ psi every couple shots (with those shots usually being wildly off from where the others were grouping). So here's a rundown with some pretty pictures.

The interior cast metal handle piece: Basically they made the longer screw slots too short by about 1-2mm, as a result the piece was not able to be flush and was really only being held on by the two front screws with the back screws digging into the holding pin for the hammer (also when those two front screws started loosening the hold handle had some jiggle). So just ground off around 1/16" of material of the two screws and now it's able to be held flush even and no more shaky/loose handle.

[linked image]

The annoying spinning barrel issue. Now the breach bushing with the green oring already had two flats milled on it ready to go but had nothing to make use of them, so just drilled and tapped a through-hole on the receiver and put in a pair of set screws on each side that hit the flats. Now that sucker is locked solid in the rear, also allowed a nice tight clamp from the front. Seems to make distance shots more consistent so far (was able to get around 50 shots between the raindrops today).

[linked image]
[linked image] [linked image]

Next up was the external regulator access port, the corners for the lower third to half of the hex nut were actually below the hole diameter so I was starting to get a fair amount of ground aluminum off the receiver trying to force the hex wrench into that. So with the whole thing disassembled mounted it up at the 15 degree angle with the hole centered and opened that up to 1/4" from the 0.206-0.207" hole that was there before, considerably easier fitting the wrench inside and making contact with the hex nut.

[linked image] [linked image]

While on the regulator I got it torn apart, cleaned out, lubed up all the orings, and then came to find out that they put in the acetal/delrin disc backwards so the conical portions were not engaging one another and that the belleville spring washers (10 of them) were arranged in a configuration that allowed virtually no compression, ie ((((())))), so got those two in order. The washer configuration I used for it ended up being ))(())(()) which seemed to provide a good tension and range of compression.

[linked image] [linked image]

The last thing I found while tearing apart and cleaning the firing pin assembly was that the tension spring was in backwards so put that in so that correctly so the large end was in the metal section and the small end was properly in the acetal/delrin post. Also as I found out make sure that the threaded nut is screwed in far enough that half the threads are visible, much less than that and you have the possibility of a spontaneous leak that drains your cylinder in fairly short order.

[linked image] [linked image]

So that's been about all the fun there, I need to re-zero in my red dot after having torn everything all apart. Not having any gun-related fliers for shots now, and the chrony readings are stabilizing and not having 100+ fps random swings. Last 9 shots after adjustments averaged around 662fps at half tank.

 
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AuthorReply

db
(Login Diamondback)
YC

Nice post! Looks like owners could drop a small washer or 2 in those grip

May 26 2017, 4:49 PM 

screw holes to act as spacers & tighten that grip piece up?

 
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Alex in Upstate NY
(Login awilde)
YF12

If you can find some that fit sure

May 26 2017, 5:44 PM 

Didn't have any luck on my end, everything we had around the shop was too big and jutted out without grinding/filing edges. Took less time and effort to just grind the screws a little shorter in my case.

 
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Rick
(Login pluric)
YF12

Great information

May 26 2017, 4:52 PM 

Thank you for taking the time to post all of that and the photos REALLY help.

 
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gubb33ps
(Login gubb33ps)
YF

KInd of an "atta boy" review

May 26 2017, 6:58 PM 

Don't think the MK1 is much different than the MK II in internal respects. Could put a set of MK1I grips on it and adapt a MK 11 shoud to the same barrel if it makes you think it mattered.

By set screwing the bushing, as you've done, would be able to make tightening eaiser and still allow for rotating the barrel is needed. Also lets the concept of barrel tensioning (which is what the original desight of not locking the barrel in place allowed) by the shroud to work.

I really haven't had any barrel bushing spin issues with the MK I...so long as I kept my thumb clamped down the back end of the bushing, it would tighten up past the point of spinning as I tighted the barrel nut.

I did try rotating the barrel while critically squiting down the barrel trying to find the spot where the bor was really centered to the end cap exit hole. Not too surprizing, there were placed were were places were it was a little off center...enough to clip? doubt it, but figured getting it dead ceter really avoided that possiblity best.

photo c3974d81-2cf3-4296-a852-5f2fe0a74a52.jpg

(its a longer distance from the end of the barrel and the end of the shorud-cap in a MK1 Samel length shrouds, but the MK 1 barrel ends aboutr 1" shorter inside that shroud...A MK II would have a shorter "jump" to end cap, so maybe less critical in centering. At least in my .22, the shroud cap's hole only runs about .238-9"..which ain't that much slcak for a .221-.222" pellet.)

The regulator was fussy on mine. Started off barely being able to tell it was regulated. But the more I shot it, the more it started actiing as you'd expect a regulator to act. Rather than take it apart, I just kept shooting...and it kept getting better and better.

Something you should look at in most of the published strings (not cut off sections for-show) show the very first one or two shots are "off" even on well broken in regs. Not just my strings, but most of the ones posted.

I gave up trying to fix that, and just "dump in the dirt" two shots before going on to antyhing serious.

OK..an example, which shows I still have some ways to go. In my case, am trading speed/energy for shot count rather have +40 11 foot pound shots).

The "DIRT SHOTS" are just expected to be odd. In my case, they are usually low. In other published strings, they seem to be higher than normal.

MAY be (in my case) somthing to do with the multiple hammer-puse effect of pump-filling...pehaps 30-35 little taps with an air hammer" than one "push" of a tank fill?

photo 9fcf167c-09e2-4f78-9b32-391ec604177c.jpg

Without doing a ding-dang-thing other than shooting the "carp" out of it nearly every day for a month, no changins in spring tension/transfer port restriction, regulator, or anything else (just shooting it in for a WHOLE LOT LONGER than I ever expected to have to)...comes out like this:

photo 4bef7840-5a08-40c6-b20b-d95ad2545e39.jpg


So eventually, this one stopped doing the "off shots" after filling that I use to just dump in the dirt, the shot strihg got both longer and tighter (more shots in 2%R than I got in 3%), and the energy increased very-very slightly.


Evendenly, it if you aren't wiling to dissasemble and smooth out the regulator manually, it will self-smooth with enough use (at least in one example).

Go though this whole post because I do find these pistols to be a particually good value...a really regulated, really accurate, small, light weight, PCP pistol for less than $300?

Too good to be true?

Nope...may be too much for the snobbish to believe a cheap Chinese regulated pistol can manage it....but thats about preconceptions rather than facts.


EDIT: about red dots.

Tried bigger...tried smaller. Decided I just was not willing to give up "click" adjustments for screw (which anything small has). So that simple small red dot gets the go-ahead.


    
This message has been edited by gubb33ps on May 26, 2017 7:08 PM


 
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Bob
(Login bpratl)
YF12

Great Post

May 27 2017, 6:12 AM 

Alex, thanks, there is a lot of great information in your write-up. I have already found one of the long 3mm screws that hold the grip casting to the frame stripped because it bottomed out on the hammer pin and I had to mill out the slot re-tap it to 4mm. Now I have to totally disassemble it to check for other assembly errors. It is oblivious that someone new assembled your MK II and it's a good think that you QC'd it. I'll update my findings after a complete inspection. Bob


    
This message has been edited by bpratl on May 28, 2017 7:00 AM


 
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Terry E
(Login TleVta)
YF12

Question on the shim stack:

May 27 2017, 7:24 AM 

I like what you did for more compression, but how do you determine which direction all of them go?

I ask because I just replaced the O-rings in my Marauder reg, and they were stacked like this:

()()()()

Would that same sequence be too much?

Just trying to learn something here.

 
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Bob
(Login bpratl)
YF12

I was just wondering the same thing.

May 27 2017, 7:43 AM 

Are there 8 or 10 washers?

 
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Alex in Upstate NY
(Login awilde)
YF12

RE: Bob and Terry

May 27 2017, 9:16 AM 

When I got the regulator disassembled there were a total of 10 belleville spring washers and they were in a configuration of ((((())))) which basically meant they had all of a fraction of a turn (and a bloody hard turn at that). I did some looking around at many of the standard formations and eventually settled on doubling's formation ))(())(()) since it more or less lined up with the end of the piston shaft with maybe 1-2 washers worth of extra room uncompressed (these washers were extremely thin, 1/32" or less). The first time I tried with a ()()()()() they were actually ended up over the end of the piston shaft slightly and took some maneuvering to get the hex nut screwed in with the last few washers still aligned. I don't know what sizes are generally used with other similar caliber airguns, but these were tiny little things about the same diameter as a pencil eraser. Other washer assemblies I saw on youtube and various forum posts were 2-4x the size.

 
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Terry E
(Login TleVta)
YF12

Ah, now I understand

May 27 2017, 2:18 PM 

I'll try your formation when I get to that point. Thanks Alex.

 
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Alex in Upstate NY
(Login awilde)
YF12

Different amounts of turns depending

May 30 2017, 1:30 PM 

If you use the ()()()()() configuration it gives you about 8-9 full arch turns going from 45 angle corner of the trigger guard to the other (as in a |< type of arch). That one is a little tricker to get the hex nut on with the last few spring washers still aligned but gives a little less sensitive tuning. With the ))(())(()) configuration you get about 4-5 full arch turns so each turn has more impact on the regulator pressure. I just got finished getting my regulator back working again right, had to go in and also readjust both the hammer spring and trigger spring back considerably along with starting the regulator at minimum and slowly working it up.

 
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Jason
(Login nervoustrigger)
YF12

Belleville washer stack in a regulator

May 27 2017, 9:15 AM 

The way they were stacked, ((((())))), it behaved like two extremely stiff springs. Likely it was not regulating at all, just passing the reservoir pressure to the valve. Five paralleled springs on the left in series with five paralleled springs on the right.

Normally they are used in series ()()()()() to have more compressible travel and a modest spring rate.

 
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Frank Zuccarini
(Login Frank_Zuccarini)
YF

Thank you sir........

May 27 2017, 9:51 AM 

....... for this most informative post.

These guns are so much fun to work on, and now I have a few more enhancements to make. I can hardly wait.

Frank

 
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johnb
(Login john2468)
YF

thank you for info !

May 27 2017, 6:36 PM 

Thanks for great tuning information with photos no less.
I now have 3 airmax pistols. One .177 zeroed for shooting distances over 50yd and another for targets under 50 yds.
I wanted a .22 to compare with the .177s. I like the .177, quieter.
A great shooting pistol at a reasonable price. Thanks to Mike for making it happen.

 
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Alex in Upstate NY
(Login awilde)
YF12

Some more tinkering

May 27 2017, 9:25 PM 

I started looking at the shroud a bit more and it seemed like there were some features lacking which others have posted some similar machinations towards when using with the SLRS. I don't have one and probably wont need one, however I did think that the shroud needed some improvement so that it served a bit more purpose than just looking pretty and providing a little further rail mounting.

One of the main things I noticed was the little acetal/delrin split ring bushing at the rear of the shroud. I can only make an assumption that it was supposed to compression point between the receiver and the rear shroud socket however it was about 1/4" deep and the bushing was only 5.5mm in length (0.2165") so there really wasn't any contact made there and was kind of free to move about in that gap. I was able to just slip an R05 oring over the barrel after the bushing and it provides a nice compressing seal.

[linked image] [linked image]

After that I noticed that many of the various barrel shrouds on other airguns generally had air venting holes towards the rear of the shroud so that the air had an escape path while being forced back through the air space. By default this seemed to be sorely lacking as the only viable means I saw were through the tiny gap at the edge where the shroud meets the receiver (could sometimes see a tiny bit of oil off shot pellets making its way there along the edges). So to remedy that I added in a simple cross sectional set of holes 1/16" in diameter just forward from the socket where the acetal split ring bushing sits. Didn't really change anything sound wise with the pistol firing but did seem to have a fairly noticeable impact on how much recoil/impact each shot had. Before there was always a fairly noticeable jerk when the gun fired unless I held with a fairly strong (almost death) grip, with the ventilation holes it was taking a much less aggressive hold to keep the gun steady during shots (still firm, but not nearly as bad).

[linked image]

 
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H.E. Potter
(Login Hepotter)
YF12

I put the O-ring on the breech side of the bushing, seems to seal better! nt

May 29 2017, 10:25 PM 

Hepotter

 
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Bob
(Login bpratl)
YF12

I followed Alex's foot steps

June 1 2017, 6:39 AM 

My MK II must have been assembled by the same assembler because I found the same errors and did the same modifications as Alex recommended. I'm still a little confused on the regulator Belleville spring assembly. I set mine up the same as Alex's so I will give that a try.
Has anyone tried ()()()() configuration with 6 or 8 washers instead of 10? I may give it a try after I break it in. I highly suggest in doing what Alex did because after a total disassembly, inspection and cleaning I feel very confident on the gun and it's inners.

 
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