Author Topic: CZ trigger job - Over travel fix  (Read 5719 times)

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Offline DanT

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CZ trigger job - Over travel fix
« on: February 15, 2017, 01:49:52 PM »
Comment 4/10/2017: This thread is a continuation of an earlier one.  If interested, also see:

http://www.czfirearms.us/index.php?topic=86073.0


- DanT  Phoenix, Az


After fine tuning the trigger pull length and reset distance, the trigger "over travel" became more noticeable.

There is a "over travel" foot on the stock trigger on the front left of trigger.  Adding a small foil shim removed the over travel.  Add too much shim and the trigger will not "fire".  Start by adding too much, then reduce the number of foil layers until the trigger starts working again.  Glue it into place with some quick set, two part epoxy. I used the quick set version of "J-B Weld", "J-B Kwik".

Pretty simple adjustment.



The above is a composite of four modifications to the stock trigger:

1) 0.0075" aluminum foil shim under the "over travel" trigger foot.  No more over travel.
2) 0.025" brass shim under the disconnector foot.  Short trigger reset
3) ~0.30" brass + aluminum foil shim under the rear trigger feet to shorten the trigger length
4) In order for the safety to now work, 0.015" was removed from the top of the rear trigger foot.

It seems to work pretty well.  When I figure out how to upload the demo of the trigger performance, I will add it to the next post.

DanT  Phoenix, Az
« Last Edit: April 10, 2017, 02:46:46 PM by DanT »

Offline DanT

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Re: CZ trigger job - Over travel fix
« Reply #1 on: February 15, 2017, 05:50:16 PM »
Ok, another "do over" on the video.  After further review, the first one seems a bit silly with very little information.

Sorry, the focus is not great at the start, but it does come into focus later on.  The pictures above are better than the video to see what it looks like inside.



I am really happy at how well it is working now with short trigger pull, short reset, plus removal of the trigger over travel.

If anyone wants me to do this to your trigger, message me.

- Dan T   Phoenix, Az

Offline Obiwan

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Re: CZ trigger job - Over travel fix
« Reply #2 on: February 15, 2017, 07:09:12 PM »
Thanks for the nod to JB kwik weld. As you recall, in the other thread I was thinking a small welding blob. Seems like JB should be cleaner. Instead of using shims, I plan on putting a small blob of JB under the trigger and disconnector feet, letting it set, then filing it down to the proper travel distances. I'm thinking it has the same effect as using shims. I mean, it doesn't matter if you add metal at the bottom (shim) or top (bottom of foot), right? Any thoughts or concerns with that approach?

Offline DanT

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Re: CZ trigger job - Over travel fix
« Reply #3 on: February 15, 2017, 07:23:54 PM »
That seems like it could work.  If a shim were to fail, it would simply cause increased margin once again (i.e., "fail safe").  I prefer to epoxy to the painted surfaces because it is a bit easier to force them to release the next time I want to change things.

However, at this point with the remaining trigger over travel fixed, it is as good as it can get.

- Dan
« Last Edit: February 15, 2017, 07:48:05 PM by DanT »

Offline SouthernScorp

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Re: CZ trigger job - Over travel fix
« Reply #4 on: February 15, 2017, 09:14:14 PM »
how safe/reliable is all this modifying a fully field tested trigger system with glues and shims, and blobs...
CZ Scorpion Evo S1 Pistol:

SLR Synergy Mini comp
SBT-EVO Brace
PMM Safety Levers
Dual HBI Prostock Charging Handles
Gearhead Mag Release
HBI Trigger Spring
HBI Delta Trigger
PMM QD Front & Rear
Magpul MS1 + QDs
Holosun HS515cu on ADM low mount
Vendetta VP-17-A AFG

Offline omnidj

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Re: CZ trigger job - Over travel fix
« Reply #5 on: February 15, 2017, 09:53:24 PM »
You folks are braver, or more experienced for sure (or crazier) than i am. I can replace springs, maybe even polish a surface or two, but this...? Kinda falls into the "Professional Driver on a Closed Course" category for me. Very interesting info, though

Offline DanT

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Re: CZ trigger job - Over travel fix
« Reply #6 on: February 15, 2017, 10:09:46 PM »
Others are making similar modifications, but changing the metal parts themselves.

Take a look at this just past the 6 minute mark. 



Very sporty.  Here are the trigger kit parts as pictured:

https://czcustom.com/czc-parts-made-in-the-usa/cz-evo-trigger-pack-czc.html

This parts kit has pre-travel/over-travel adjustment screws, smaller trigger hooks (shorter trigger travel), a shorter rear hammer shelf (shorter disconector travel), and has the needed safety offset built into the trigger part.

One is a set of new custom parts (hammer/trigger), the other is a set of custom shims.  They are both performing similar functions.  One is fixed, the other is adjustable.  One is prefabricated (nice!), the other is custom built.

However, in either case, margin has been removed in order to provide higher trigger performance.  The stock trigger has huge margins: 10 lb. trigger weight, very long trigger pull, and very long trigger reset.  With the shim approach, you can set the performance to whatever level you wish.  What is shown is much, much better than a stock trigger, but it is not match grade.  I think a fundamentally different trigger design would be needed for that.

It comes down to what you like in a trigger.  Lots and lots of margin, or shorter, higher performance.  I have some custom CZ pistols (from the CZ custom shop).  I like higher performance triggers.

In the case of the changes I have outlined above, the shim sizes could be reduced to introduce additional margin (longer pull/reset) to fit personal preference.  As I have said in an earlier thread, the shims (particularly the reset and trigger pull) can be prototyped completely out of folded aluminum foil shims to allow you to get a feel of the end performance at no risk other than wasting some kitchen aluminum foil.

It is nice however, when the performance is exactly what you want, to measure the thickness, find the closest available larger metal size (like 0.032" brass -> 0.030" or 0.008" brass -> 0.007"), and then file to fit.  I plan on doing that with my rifle, but have not gotten there yet. 

The use of epoxy to hold the shims in place is not a problem.  I have to put it on the top to keep it from raising the shim and affecting the thickness. Thus the "blob". Try to take the front barrel off and see how well mere Locktite works holding things together.  Epoxy is quite a bit more substantial than that.

- DanT  Phoenix, Az
« Last Edit: February 16, 2017, 08:18:37 AM by DanT »

Offline kyron4

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Re: CZ trigger job - Over travel fix
« Reply #7 on: February 16, 2017, 03:34:31 AM »
Have you shot it with the mods to the trigger. I wonder with a short travel and reset if doubles and/or unintentional bump firing would occur, especially with gloves on.

Offline DanT

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Re: CZ trigger job - Over travel fix
« Reply #8 on: February 16, 2017, 08:17:49 AM »
Have you shot it with the mods to the trigger. I wonder with a short travel and reset if doubles and/or unintentional bump firing would occur, especially with gloves on.

I have taken these changes to the local range (C2 tactical) to test them.  It is not a problem.

I would think using gloves you might want more margin.  That is not a problem.  The shims can be sized to fit the margin.

If you want, you can take a very simple half step that leaves lots of margin in place and requires no other changes to the trigger.  The original change I made used 0.016" brass shims for both the trigger shim and the disconnector shim.  This removes 41% of the long trigger pull and roughly half of the long reset.  That change is still a big improvement.

0.016" brass strips is a standard size, so it is easy to get.  0.016" on the trigger foot requires no filing changes to the top of the rear trigger foot as the safety just clears.  Here is a shot of the trigger when I had 0.016" shims in place for both the trigger and the disconnector:



That is a dead simple drop in with lots of margin.  You just need to place the shims and "blob" them in place, catching the top of the shim and the metal around it.  "Blobing" epoxy over the top (rather than under the bottom) keeps the thickness right, especially for the rear trigger shim.  With this setup, the trigger over travel will not be noticeable, so there is no need to put a shim in place there.

If you don't like it, you can pull it back out and have zero changes to the trigger.  However, if you then decide you want more, you can pull it out and put these larger changes into place.

If you want, ping me and I can send you these two 0.016" shims for a couple of bucks.  However, 12" long, 0.016" thick brass strips are very available on amazon.com. The rear trigger shim is a bit over 3/4" long (7/8"?) by 1/8" wide. The disconnector shim is 1/4" long and 1/8" wide. The dimensions are not at all critical, just the thickness, 0.016".

- DanT  Phoenix, Az
« Last Edit: February 16, 2017, 11:07:50 AM by DanT »

Offline DanT

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Re: CZ trigger job - Over travel fix
« Reply #9 on: February 17, 2017, 05:49:39 PM »
At the range this morning, I got a "double".  I.e., two bullets for the price of one pull.  That means the disconnector shim of 0.025" was a bit too much and did not quite catch all the time. 

I don't really want to file the 0.025" brass shim down to 0.020", so I have ordered some 0.020" brass sheet for a thinner disconnector shim.  In the meanwhile I dropped back to the 0.016" disconnector shim I was using before, while still using the 0.030 to 0.032" trigger shim.

So until I get the 0.020" brass stock, the reset is not quite as short, but still works with the short trigger travel.  However the longer reset length does have a side benefit.  The 0.016" reset shim causes the rear trigger shelf to just "bump" the disconnector right before firing the trigger.  That "bump" can be felt in the trigger as a bit more resistance just before firing.  It makes it "feel" like a a two stage trigger (some trigger take up, then a bit more resistance, immediately followed by a trigger break). It is kind of nice to feel right where the trigger is going to fire.

Disconnector fully applied (left hook on trigger shelf) using 0.025" shim (wrong side of marginal):


Disconnector fully applied (left hook on trigger shelf) using 0.016" shim (very robust):


0.020" would be halfway between the two.  I think it is good to visually see the difference between "just barely marginal" vs. "very robust"

Here is today's "final" view:



I figured out that I only needed a small shim under one of the two rear trigger feet (not both).  Less shim, more "blob". That makes for a smaller, lighter shim that is less likely to "let go" under recoil. 

Bottom left: 0.007" trigger over travel shim
Middle: 0.016" disconnector shim (a common brass thickness) - robust, but may move up to 0.020" (less common brass thickness)
Bottom right: 0.032" trigger shim (a common brass thickness)

plus a HBI disconnector spring, softer trigger spring, and 0.015" removed from top of rear trigger (upper right) for clearance for the safety.

- DanT  Phoenix, Az
« Last Edit: February 18, 2017, 12:02:37 PM by DanT »

Offline DanT

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Re: CZ trigger job - Over travel fix
« Reply #10 on: February 18, 2017, 11:59:58 PM »
I did a better job with the overall travel.  I got some 0.013" metal sheet in today and it still allowed the trigger to fire when used as the over travel shim.  When you go too far with the overall travel shim, it will block the trigger from firing.

The trigger fires at around 0.039".  If we have 0.013" of over travel on top of that,  then the total trigger travel length is at least 0.052".

The "simple,  conservative" change is 0.016" for the trigger shim.  That is removing 16/52 or 31% of the total trigger travel.  However, since the over travel is so long, removing 0.013" of over travel on top of that means that overall 55% of the total trigger travel (0.013" + 0.016" removed) be removed by also cleaning up the overall travel.

Over travel is not really a useful margin from a safety point of view.  It does help manufacturing by allowing a bunch of manufacturing variation and still have a working firearm.  However, it does not help safety.  Getting rid of the overall travel "tightens up" the feel of the trigger quite a bit without giving up any "safety" margin.

Thus, the conservative setting can remove 55% of the total trigger pull length.  This is:

0.016"  trigger shim
0.016" disconnector shim
0.013" trigger over travel shim
No metal removal needed for clearance for the safety.

The "sporty" setting looks like:

0.032" trigger shim
0.016" disconnector shim
0.013" trigger over travel shim
Plus metal removal for clearance for the safety

This leaves roughly 0.008" (plus a tiny bit of over travel) out of 0.052". This removes about 85% of the trigger travel.

15% trigger travel (sporty) vs. 45% for conservative.  I supose you could set the trigger shim to 0.025" and get something in between these two (29% trigger travel - less metal removal needed).

I guess the main message is that removing  over travel can tighten things more than I initially thought. That is potentially 20% of the trigger travel for nothing from the user point of view.  The trigger travel is now a bit tighter than the video for the "sporty" version.

- DanT  Phoenix, AZ
« Last Edit: February 21, 2017, 03:21:15 PM by DanT »

Offline Coleman

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Re: CZ trigger job - Over travel fix
« Reply #11 on: February 19, 2017, 12:30:27 PM »
Nice write up DanT always good to see others not afraid to dig in and make things work

Offline DanT

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Re: CZ trigger job - Over travel fix
« Reply #12 on: February 23, 2017, 08:07:11 PM »
Someone wanted to see the trigger in action.  I got my wife to grab some video for me today at the range. My son and I are both casual target shooters, so we are not speed demons. 

5 shot warm up at 25 yards.  No optics, no bench rest:


My son and I:


Here is my son Matt punching paper at the maximum indoor range limit of roughly 25 yards.




He has only fired an earlier version of the trigger and very much likes current the improvements.

- DanT  Phoenix, Az
« Last Edit: February 23, 2017, 08:28:15 PM by DanT »

Offline DanT

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Re: CZ trigger job - Over travel fix
« Reply #13 on: February 24, 2017, 03:27:44 PM »
I had a shim break loose in an extended test.  I guess it is time to scrub the paint off under the shims, ruff up the shims and the metal, and try using a bit of epoxy under the shims.

I will have to give it a day to harden and give it another try.

It is shear force that is at issue. The shock is being applied from the side, not the top or bottom.  I image some glues would be better at that than others, but that is not my specialty.

Anyone have any idea what would be the best glue here?  I am using the quick version of JB Weld.  Would super glue be better?  Other recommendations?

- DanT  Phoenix, Az

Offline DanT

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Re: CZ trigger job - Over travel fix
« Reply #14 on: February 24, 2017, 04:08:30 PM »
I did some looking on line for the best metal-to-metal glues.

"I've used JB-Weld in some situations where I thought "There's no way in hell this is going to bond" and it came through. Stuff like fixing bike frames and holding a fair amount of my old Volkswagen Vanagon together."

"Agreed - HOWEVER - J-B Kwik doesn't have a very good shear strength; use Weld, or *if* you can find it, Industro-Weld also by the J-B Weld company (of Sulphur Springs, Texas)"

Alas, I just used J-B Kwik......  Shear strength is what I need.  I will have to see how the J-B Kwik works out.  If it lets go, I will drop back to slower curing J-B Weld.

- DanT  Phoenix, Az

 

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