Author Topic: VZ08 trigger and Gremlin fix.  (Read 21524 times)

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Offline foxfyre841

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Re: VZ08 trigger and Gremlin fix.
« Reply #15 on: October 03, 2014, 06:53:36 PM »
The disconnect armature on the strange piece from czexpert is made to move only forward (toward the muzzle).  Rather than maintaining contact with the carrier via it's length or spring pressure, it simply prevents an additional reset on the forward stroke of the carrier.  If it were long enough to maintain contact with the carrier after contacting the nub, it couldn't pass the nub in the first place. 

The best way to alleviate this is to either increase overtravel (can't be done aftermarket because you'd have to add metal to the sear-foot/disconnector-protrusion interaction surfaces) or to change the reset point to precede the sear/striker interaction on the return stroke.  This is literally the only way to alleviate reconnection when issues stem from:
 1) half releasing the trigger before the striker passes over the sear as moving rearward and then re-pulling the trigger (trigger slap)
 2) not enough over-travel built into the sear/disconnector such that the push down of the sear naturally pivots the foot forward of the protrusion.  (this can be alleviated by both increasing the sear spring strength and also reducing the vertical width of interaction between the sear and striker THOUGH THIS IS DANGEROUS: the striker may be only barely caught and then release unexpectedly such as when you bump it while aiming at your lover, wife, kid, mom, etc DO NOT MESS WITH THE STRIKER AND SEAR ENGAGEMENT SURFACES).

So: tabbing or get the old Ohio Rapid Fire compliance kit.  Or see if whoever holds ORF's patent on the forked disconnector will start making them again.

Here's a neat patent on the tabbing option that shows sear, disconnector, striker, carrier interactions really well!
http://www.google.com/patents/US7676974
Patent is owned by Vladimir Zemanek?

PS: I don't know what steel the carrier is, but it has every indication of being cast steel.   Ideally the process is as follows:
Make sure your welder knows this is cast steel and applies pre and post heat treatment.   (heat it with propane torach, keep it warm and let it cool somewhat slowly for the first time.)  If using low carbon steel (cold rolled LC or a36): after welding shape the tab with file, polish it, and heat the tab to cherry and dunk in casenit. Do this twice and it should be somewhat hard.
Otherwise, grab some 4130, a516/a514 and weld up with a pre&post heats.  Normalize (just the tab) once (heat to cherry and air cool).  Then heat the tab to cherry, dunk in oil, and place in oven at 450-500 for 2 hours. 

Though I'm sure a lot of tabs are just plain-jain 1018 low carbon or pickled a36 hotroll and will last a long time.  So the above isn't probably necessary, just would be ideal for longest service.  Just make sure the tab isn't harder than disconnector cause the tab can have a bead welded on top to extend if it wears; the disconnector cannot/should-not.


Offline RSR

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Re: VZ08 trigger and Gremlin fix.
« Reply #16 on: October 04, 2014, 01:50:16 AM »
Okay, I was a little mistaken on how the full auto trigger works:

Under both full auto and semi auto, both the left and right sears are active.  The thicker right sear prevents the striker from traveling forward except when bolt carrier is all the way in battery -- it drops from the striker once bolt carrier is in battery and is up whenever the bolt carrier is not completely forward in battery.  The thinner left sear is what releases the striker whenever the trigger is pulled.  The lever that deactivates the thicker in battery sear is activated by the bolt carrier protrusion, opposite side, that activates the semi auto disconnector.

The only difference in rifle function between full and semi auto is the sears that extend from the full and semi auto disconnectors that extend from the trigger.  The semi auto has the upward protrusion.  The full auto does not.  What happens is that when the bolt carrier first crosses the semi auto disconnector, moving to the rear, is that the narrow right sear is disconnected/released up from the trigger by that movement.  To fire again, the trigger needs released/reset and then pulled again.  Under full auto, whenever the trigger is pulled that narrow left sear stays down regardless of bolt carrier movement. 
Moving the safety forward allows the full auto disconnector to interact with the left sear, while moving safety to the rear allows the semi auto disconnector to interact with the safety...

Obviously different than my original understanding that sears/disconnectors were paired...  And obviously when the semi auto conversions remove roughly one half of the fire control group/sear mechanism, it's easy to see why the gremlin occurs.  Moreover, it is now apparent to me that the gremlin is also related to not quickly enough releasing the trigger -- didn't fully understand before.  So if you hold the trigger back and rearward movement is sufficient to disengage the sear via disconnector but the bolt/striker also pushing sear down so far that it reengages the sear (still having your trigger not fully released seems to be key).  Continuing further, jerky trigger pullers would conceptually have less issues than those with good trigger control where pulling all the way to rear through firing cycle and holding to rear until releasing while re-establishing sight picture before pulling again...

The disconnector/sear reset is only about 1/8" to 1/4" of movement.  You can see by (with unloaded weapon) and top cover off.  Hold trigger to the rear.  Push down on disconnector upward protrusion.  It'll release the sear.  Then push down on the sear (continuing to hold trigger to the rear) to see when it re-engages. 

All that the tab does is re-release the semi auto disconnector before the sear has a chance to cross a lowered sear due to momentum, etc. 





Videos:




Offline Varickm

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Re: VZ08 trigger and Gremlin fix.
« Reply #17 on: October 08, 2014, 08:44:55 PM »
foxfyre841 -- thanks for sharing.

Yes, it looks like the extended disconnector accomplishes the same effect as the tab, but it does on the disconnector side rather than the carrier.  Interesting nonetheless.  Haven't seen the ORF parts before, very cool.

The VZ58rifle.com part, I think due to the pivoting disconnector it functions similarly due to the pivoting upward portion of the disconnector -- increases the range/length of interaction between the carrier and disconnector just like the tab and the ORF disconnector do. 

The Hermex effect is what the tab and the ORF part attempt to rectify, as does the VZ58rifle.com part as well. 

The other issue mentioned by the VZ58 site is the side to side play that results in you sometimes needing to pull the trigger twice to release the striker when using the original trigger group and semi auto sear only -- e.g., the small sear in your photo not the wider one as utilized by bonesteel and century.   Somewhere there's a video out of Canada of them using the base of a 22lr casing as a spacer on the sear pin to accomplish the same (looks like the VZ58rifle disconnector prohibits the sear from that lateral movement).

In full auto, both the left (from shooter perspective: narrower, semi auto) and right (wider, full auto) sears catch the striker in semi auto (due to full auto mechanism, the full auto striker releases automatically when bolt carrier is in batter, allowing the trigger pull to release the semi auto sear once pulled).  Full auto, just the full auto catches the striker when the trigger is released.  As the semi auto sear was never intended to arrest the striker on its own and is more delicate than the full auto sear, conceptually the semi auto sear is a potential failure point.  Whether that is actually a problem, I don't know -- but something to be mindful of.  Again, the bonesteel or Century trigger group with the wide sear should make this sear failure null and void.

I've personally seen the "side to side play" issue twice with the Bonesteel fcg. The parts were deburred too aggressively by the manufacturer. The axis pin holes were bevelled too deep, causing excessive side to side movement. It doesn't take much.
« Last Edit: October 08, 2014, 10:48:39 PM by Varickm »

Offline Rob2966

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Re: VZ08 trigger and Gremlin fix.
« Reply #18 on: October 14, 2014, 02:20:02 PM »
Just bought 2 vz2008, both have disconecter that is flat on top, put 120 rounds through each, no failers at all. Is it still a good idea to add tab? Or is problem fixed?

Offline RSR

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Re: VZ08 trigger and Gremlin fix.
« Reply #19 on: October 14, 2014, 03:30:59 PM »
Just bought 2 vz2008, both have disconecter that is flat on top, put 120 rounds through each, no failers at all. Is it still a good idea to add tab? Or is problem fixed?

Without a tab, the problem is never truly fixed.

Offline Rob2966

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Re: VZ08 trigger and Gremlin fix.
« Reply #20 on: October 14, 2014, 03:44:30 PM »
Thank you RSR! I Will be sending carriers out to Morgan tomorrow!

Offline RSR

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Re: VZ08 trigger and Gremlin fix.
« Reply #21 on: December 03, 2014, 03:14:35 PM »
Okay, looking at the trigger function further...

Most of what I wrote previously still applies to some effect (last update described function with trigger pulled, whereas this is a little more full function), but the mechanism is more simple than I previously indicated.

Effectively, the only difference between full auto and semi auto is this:

The safety on full auto holds the left disconnector -- with the hump, same one is our guns -- low enough that the bolt carrier does not contact that protrusion, so the disconnector and the semi auto sear remain engaged and only disengagement is from releasing the trigger forward.
The safety on semi auto allows the left disconnector to raise slightly so that the upward protrusion is pushed down every time the bolt carrier crosses it, thereby releasing the sear up to grab the striker forcing the user to release and repull the trigger for each shot.

So the right "full auto" sear actually functions in both firing types/all the time in concert with the left "semi auto" sear, which also works all the time.
The right sear is connected to a lever/disconnector extending forward (pivoting on trigger group pin) and ending with an upward protrusion that ends just before the bolt hold open (same part but opposite side, the lower rear bolt carrier protrusion) pushes this lever down when bolt carrier in battery, which prevents the striker from moving forward unless the bolt carrier is all the way forward and round in battery.  Once the bolt carrier is all the way forward, this sear releases from the striker.
The left sear is connected to the trigger and functions the same all the time.  The only difference in function is how the disconnector is and whether the bolt carrier is disconnecting the disconnector from the sear (semi auto) or not (full auto).

Offline RSR

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Re: VZ08 trigger and Gremlin fix.
« Reply #22 on: December 03, 2014, 07:24:24 PM »
Continuing, the standard gremlin looks to have two primary causes, both of which the tab solves in different ways.. 

The first is when the bolt carrier travels backwards and hits the disconnector, releasing the sear. The bolt carrier then crosses the sear -- at this point it could potentially push the sear down far enough that the disconnector re-engages the sear.  Then hitting max spring tension it moves forward but the bolt carrier recrossing the disconnector (and releasing the sear up)  occurs too late for the striker to be grabbed by the sear. 
The tab solves this one by rehitting the disconnector earlier so that the sear has time to travel up and grab the striker. 
This is also the gremlin that can be temporarily fixed by adjusting the trigger lever spring up for more tension.
This seems to be the most common standard gremlin issue w/ the century guns and is only replicated when firing.
*And probably is rleated to holding the trigger to the rear while the above is occuring.  Fairly confident but not certain on this.

The second is related to the first but differently.  Essentially, by holding the trigger to the rear the sear and disconnector engagement is so strong that the bolt carrier jumps rather than releasing the disconnector.  I belive this to be more of a problem with mil spec trigger groups.  I do think Century likely made their sear a little taller to prevent that from happening (need to get a milspec OEM to compare). Mil spec due to the same disconnector pulling the trigger in both semi and full has to be exactly sized so that both function properly. With semi, too tall isn't a problem where the same sear in a full auto gun would have it behave like a semi when at full auto setting.
To the tab, it prevents by making the bolt carrier and disconnector interaction longer timewise and associated angles force so that the "jumping" can't occur.
This can be replicated with cycling your bolt carrier while holding the trigger to the rear.

And again, on full auto guns the right sear is connected to a lever that only drops the sear when the bolt carrier is in battery.  So all other times that sear is up to ensure striker is held back...

And the secondary gremlin is the lateral movement of trigger, sear, or safety pins/components.
« Last Edit: December 03, 2014, 07:29:40 PM by RSR »

Offline RSR

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Re: VZ08 trigger and Gremlin fix.
« Reply #23 on: January 02, 2015, 02:23:29 AM »
A little late on getting these posted, but here are the comparison pics I promised.

Trigger sets.  Early VZ2008 top and newer bottom.  Note that bottom has a more ramped rear to prevent the bolt carrier from jumping the disconnector when trigger is held to the rear.  Also, that nub sticking out on the disconnector grabs the sear. 


In this pic (of the Bonesteel/CNC Warrior Sear, not my pic -- it's very similar to the century -- the red circle is what is grabbed by that nub on the disconnector -- when pulling trigger rear, disconnector moves forward which grabs the sear and rotates the sear down). The green circle is what grabs the striker, and the arrow would be roughly up in your receiver. 
When pulling the trigger, the initial takeup is what you feel until the disconnector touches the sear part in that red circle and the disconnector engages the sear from the side visible in the pic...  Only tension you feel in first stage is from disconnector spring compressing and also causing friction between the disconnector and safety as disconnector pushes up against safety in that safety groove. 
The spring tension from the levers and friction between the sear and striker would be the 2nd stage until striker moves forward.  You would feel these in harmony.  By polishing and greasing sear/striker, you'd minimize that friction and primarily just dealing with spring tension at that point (well tension from stage 1 remains/is cumulative but it's very minimal).
Polishing the face of that sear ledge (the one oriented up and down) in center of green circle and greasing there should improve trigger function while also remaining safe while also polishing forward portion of lower striker that interacts with the sear (you are responsible for your modifications to your firearms.  Proceed AT YOUR OWN RISK and ensure proper trigger function PRIOR TO PUTTING AMMO IN THE WEAPON!).  You could also polish disconnector/safety parts that interact (upper ledge of disconnector behind the hump and safety groove) and grease those but benefits will be minimal as you can feel with very light initial trigger pull.  Greasing sear pin and/or polishing internal sear hole wouldn't hurt either.  Same for trigger pin/sear hole (remember to remove the very small roll pin holding in your trigger pin before hammering on it... I made that mistake the first time I disassembled and it resulted in lateral trigger movement after install...  Fortunately, that pin is long enough to be reversible, put dented end up.).
After striker moves forward and gun fires, you then have to
1) release the trigger to reset so that the trigger moves forward far enough for
2) that nub on the disconnector to move far enough back to grab/re-engage the sear lip. 
To mess with reset distance, you would have to play with disconnector nub locations and/or sear lower lip locations/angles.  Conceptually, the further forward the lower sear lip or the further back the disconnector nub, the shorter reset you'll have.  Again, only alter fire control group components AT YOUR OWN RISK.  *For polishing I'm talking very light, like a little flitz paste or 1000+ grit sandpaper enough to smooth...  REITERATING AT YOUR OWN RISK and TEST FUNCTION BEFORE PUTTING AMMO IN THE WEAPON!  Every weapon is unique and concepts don't always translate to practical effectiveness, nor have I T&Eed these mods yet.


Except for when the sear grabs the striker, spring tension holds the striker tightly to the rear of the bolt carrier -- the striker crosses the sear when moving to the rear and can push it down so much that the sear re-engages with the disconnector, begin held down.  The downward protrusion of the bolt carrier immediately before the striker is what releases the disconnector from the sear (allowing the sear to spring up under pressure of the lever springs -- it hits that upward hump on the disconnector).  When the bolt carrier rearward travel causes sear-disconnector re-engagement, you can get the gremlin as there is not enough time/distance between that downward protrusion of the bolt carrier and the striker for that re-release to be effective, hence the tab which causes the release earlier allowing sufficient time for the sear to rise to catch the striker:
(Not my pic)


Safeties -- newer VZ2008 top and earlier bottom.  The safeties and or trigger packs can move horizontally, which prevents the disconnector from rising (gap on safety would face down) so that the trigger can pull.  The more recent one has this gap widened considerably to prevent horizontal movement from preventing the weapon from firing, earlier just had a small ramp ground to guide it into the notch.  Neither add'l grinding is present on OEM.

EDIT: Looked at earlier again today, and I'm confident that those bevels (both side on semi auto slot, one side on full auto) are in fact the factory design -- so original safety was unmodified...

Disconnector -- this is a demo model full auto trigger, so ignore the cutout -- it's specific to the demo, wouldn't be there on OEM weapons and just is there to allow you to see the disconnector/sear interaction.  Regardless, the Century and OEM disconnector on the early versions are identical -- no difference in heights or lengths to the rear where it matters or the nub locations...


Trigger -- Century uses OEM triggers but grinds them to prevent full auto component installation.  Here you can see grinds -- cut off far left ledge in pic, and cut down from left disconnector in pic and then across as well to notch out the top 1/2 of that portion of the trigger.  *And you'd need to do substantial modification to your receiver to fit in the full auto components as well.  Don't do it.
« Last Edit: March 10, 2016, 10:39:47 PM by RSR »

Offline CitizenPete

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Re: VZ08 trigger and Gremlin fix.
« Reply #24 on: January 02, 2015, 06:21:42 AM »
Quote
To mess with reset distance, you would have to play with disconnector nub locations and/or sear lower lip locations/angles.  Conceptually, the further forward the lower sear lip or the further back the disconnector nub, the shorter reset you'll have.  Again, only alter fire control group components AT YOUR OWN RISK.  *For polishing I'm talking very light, like a little flitz paste or 1000+ grit sandpaper enough to smooth... 

If you attempt mods to improve the reset, can you please please please measure the trigger travel and rest characteristics before and after, while photo documenting your mods in stages.  To the best of my knowledge, nobody has attempted (or successfully accomplished) reduced trigger reset distance and feel.  This sear/disconnector mod, if successful, would be a major improvement and key at least for me. I would love that crisp break and short reset on a VZ.

My guess is that your utilizing your training cut-away rifle in part to analyze the function of the FCG mechanism.  Have you used any marker or chalk of some kind to determine the exact interaction points of the components esp. related to reset?
« Last Edit: January 02, 2015, 06:41:41 AM by CitizenPete »
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The post above is opinion, and I am probably totally wrong, so please pardon me if I offend anyone in any way. I am speaking only for myself and just sharing my thoughts, not trying to start an argument with anyone, and if you disagree with anything I have said, I concede your correct.

Offline Airacuda

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Re: VZ08 trigger and Gremlin fix.
« Reply #25 on: January 02, 2015, 07:21:40 AM »
I tried this about a year ago and could not get the rifle to function with a shorter reset. I believe you would have to make some custom parts to get it to function. I just got used to the trigger.

Offline RSR

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Re: VZ08 trigger and Gremlin fix.
« Reply #26 on: January 02, 2015, 04:19:09 PM »
My guess is that your utilizing your training cut-away rifle in part to analyze the function of the FCG mechanism.  Have you used any marker or chalk of some kind to determine the exact interaction points of the components esp. related to reset?

Disconnect reset is simple -- it's the relinking of the disconnector nub and sear lip.  Disconnector has to travel rearward for that to happen, which means releasing the trigger.  That's the extent of the "reset."  And why you sometimes have to pull the trigger twice if you don't let it go far enough forward prior to pulling it again...  I'm probably going to polish and lube at some point, but highly doubt I'll mess with the reset.  It doesn't bother me. 
EDIT: That disconnector nub, you'll notice the rear side is angled.  That's to allow it to push out and past the sear leg when moving to the rear and it then clicks back tight against the sear to grab it once once past...  You can see all of this with your top cover off...  Just push down on the disconnector protrusion to mimic the bolt carrier resetting it.

After striker moves forward and gun fires, you then have to
1) release the trigger to reset so that the trigger moves forward far enough for
2) that nub on the disconnector to move far enough back to grab/re-engage the sear lip. 
« Last Edit: January 02, 2015, 11:47:55 PM by RSR »

Offline TJNewton

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Re: VZ08 trigger and Gremlin fix.
« Reply #27 on: January 02, 2015, 10:37:51 PM »
Very nice analysis, RSR.  Thanks for the info and time invested.

Offline RSR

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Re: VZ08 trigger and Gremlin fix.
« Reply #28 on: January 02, 2015, 11:52:16 PM »
I tried this about a year ago and could not get the rifle to function with a shorter reset. I believe you would have to make some custom parts to get it to function. I just got used to the trigger.

The easiest route is probably to take some material off that back ledge of the sear leg...  I'd guess you could take at least 1/3rd the material w/o ruining... You could probably also try messing w/ the disconnector -- adding some more material to the for edge of that nub...

But again, AT YOUR OWN RISK and thoroughly test function PRIOR TO LIVE AMMO.  No guarantee that it will work, but it might...

Offline RSR

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Re: VZ08 trigger and Gremlin fix.
« Reply #29 on: January 12, 2015, 05:29:43 AM »
The difference between hammer trigger systems like on AKs or AR is that the striker system on the VZ58 is that the disconnector release and trigger reset is one in the same on the hammer fired systems whereas on the VZ58 they're separate.  On hammer guns you can feel the reset/hammer rise through the trigger which makes it easier (and when you feel the dual reset/hammer rise, you're then good to pull the trigger again).  Whereas the VZ58, you feel the disconnect separately and you get a much smaller tactile feedback in feeling the disconnector re-engage w/ the sear... 

This animation is the VZ58 (first one is semi auto function and 2nd half is full auto -- you can see the left disconnector with the hump sits lower in full auto so the bolt carrier won't strike and disconnect it, and the right disconnector engages/releases the right sear depending on the bolt carrier's location -- red lines are about where sear and disconnector engage as previously mentioned):


AR:


AK: