No 4 Trigger Adjustment?

Discussion in 'Tips and Tricks for gunsmithing your own Sako' started by tilleyman, Jul 29, 2021.

  1. tilleyman

    tilleyman Well-Known Member

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    Stripping down my L579 receiver for a good ultrasonic cleaning and re-oiling.
    I use a mix of kerosene and acetone which dissolves hardened goo quite effectively!

    There's some fine roll pins and springs in the No 4 trigger assembly that I'd rather leave in place, and the ultrasonic does a great job of cleaning every last crevice.

    I then blow out with an airgun, final degrease with Brake Kleen and re-oil using synthetic auto transmission fluid, thin enough to soak into all the newly clean crevices and stable over a wide range of temperatures.


    One thing struck me on re-assembly... while there are clear instructions on adjusting the No 4 weight of pull and over-travel, the protrusion height for the upper grub screw is not specified.

    Dimension AA is what I need to check... seems to be 1.4mm or so, and sets up the amount of engagement between the trigger cocking piece and the bolt striker.

    Apparently later A series No 4 triggers replaced the set screw with an integral standoff boss on the main housing.

    Sako No 4 Trigger Adjustment web.jpg
     
    Last edited: Jul 31, 2021
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  2. P04R

    P04R Well-Known Member

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    A-A distance needs to be adjusted to your gun. If the unit sits too low the sear won't catch the striker. Too high and the trigger-sear surface get bashed to pieces. You'll need to find the sweet spot where the sear contacts the trigger only on the downward motion of the bolt handle. I hope someone native can explain in better detail. I recommend using thread locker once you find the correct setting as that little screw can work loose over time leaving your trigger unit flapping in the breeze.
     
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  3. tilleyman

    tilleyman Well-Known Member

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    Thanks that was just the info I was after!
    The screw was indeed loose on mine, which is why I wanted to check what the nominal protrusion should be.
    I will adjust to my rifle... and threadlock now it’s clean.
     
  4. Old Hippie

    Old Hippie Formerly known as bloorooster

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    Question, stupid or not I’m gonna ask it. If a trigger, while in the un-cocked or fired condition, has movement side to side, is this cause for adjustment to the AA screw? Is this what has been described as flapping in the breeze?
    I have made trigger adjustments on my #4’s , only manipulating the 2 screws involved by direction. Other than that, I don’t mess with any screws smaller than the 2 action screws. My Grandpa told me not to when I was a child. I didn’t listen then, but have learned over my years that he was smarter than I gave him credit for then.

    Hippie


     
  5. paulsonconstruction

    paulsonconstruction Sako-addicted

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    Your Grandpa was a wise man. The sear engagement screw is set at the factory to have a safe & proper "engagement" of the sear surfaces & should NOT be played with. Some #4 triggers had a cut out in the housing plate so you can actually see the engagement & others did not. When the rifle is uncocked the side to side trigger movement is just a sloppy fit & has nothing to do with any trigger adjustment. If it moves side to side when the rifle is cocked, I would have some concern. If tilleyman didn't move the sear engagement screw & change the AA measurement, he should just put a drop of fingernail polish or Lock-Tite on it & leave well enough alone. Playing with the sear engagement is a recipe for disaster, IMHO. Adjusting the overtravel is rarely needed & adjusting the weight of pull below 2.5 lbs can cause the safety to malfunction. The Sako #4 trigger was designed to be a good hunting trigger for a sporting rifle. It's best to use it as it was designed. Flapping in the breeze is when your trigger sear doesn't engage the firing pin release sear when the bolt closes, resulting in a slam fire!!!
     
  6. kevinlg

    kevinlg Well-Known Member

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    Generally speaking .....I usually set that positioning screw such that the upper surface of the trigger housing is parallel to the bottom of the action.
    This usually results in the angled flats of the bolt sear and trigger housing sear engaging without one "biting" into the other.
    Since the screw's setting is held by the pressure of the housing anchoring screw, I've never sealed it's positioning.......never had one move either. Also note that I never use any commercial thread locker on trigger parts.......only fingernail polish on external surfaces.

    I'll add one more thing. Since you've almost completely disassembled the trigger assembly, you may want to prep the housing a bit more.
    I use some very fine crocus cloth(backed) to break any fine metal flashing on the internal housing bosses that the housing sear slides along......or any on the internal trigger lever holes.

    I usually clean with Gun Scrubber, and lube with Pro-Gold bolt lube and FP-10

    Note: Be careful when re-assembling the main spring below the sliding housing sear.

    Hope this helps.
     
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  7. Old Hippie

    Old Hippie Formerly known as bloorooster

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    Yes he was!
    Out of curiosity I examined a few of my rifles, and they all have a tiny bit of lateral movement, they are all in the fired condition

    Hippie
     
  8. P04R

    P04R Well-Known Member

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    The trigger does have some room to wiggle in the housing. Hard to say how much is normal. Simple enough to check if the wiggle comes from the trigger housing or just the working tolerance of the trigger.
     
  9. stonecreek

    stonecreek SCC Secretary Forum Owner SCC Board Member

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    The AA screw can only be adjusted with the trigger dismounted, so it has to be done by trial and error. That is probably the reason that Sako replaced it with a fixed bearing point on later triggers.

    The "c" screw is what holds the entire assembly to the receiver by levering against the mounting pin and should be very firmly torqued down with the locking nut ("d") keeping it from drifting. No locking compounds needed here -- but anywhere you feel the need of locking a screw, please-please-please just use some nail polish and NOT any kind of thread locking compound. Otherwise your grandchildren (or whoever inherits your Sako) will inevitably take your name in vain. The same exhortation not to use locking compound on scope mounts or action screws applies in triplicate!
     
  10. kevinlg

    kevinlg Well-Known Member

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    Hip..........

    With the trigger housing anchor screw properly tightened...........the housing should not move...solid.

    The trigger finger lever, with the bolt in the fired/ or uncocked position, should have a slight amount of lateral play/movement. If it does NOT......the trigger lever overtravel adjustment has been set too close, and can possibly create a fail-to-fire situation.
    A gross overtravel mis-adjustment can result in locking-up the trigger assembly.......requiring bench dis-assembly.

    edit: One note about the housing anchor screw. Always loosen, or tighten, the screw with the nut at the TOP of the screw. This will help prevent splitting the screw top.
     
    Last edited: Jul 29, 2021
  11. Old Hippie

    Old Hippie Formerly known as bloorooster

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    Long ago I had a Forester that I found had a loose housing, I pulled the action to clean and inspect and noticed that it wiggled just a tad. As you said ,using screw C and D I snugged it up until it was square with the receiver and carefully tightened the nut, dabbed it with nail polish. Good as new.
    I’ve really only found the need to adjust the trigger pull weight on one rifle, also a Forester, I tweaked it around for a while , dry firing, tweaking some more. I have a practice of adjustment where I turn by the hours of a clock face. Keeping track of how many hours I have turned. Its just my thing. But the trigger pull would only lighten up slightly. Playing back and forth between the weight and over travel screws. It got till it would not lock into cocked position. I turned back the over travel until it would lock again…checked for slamfire , it was good. I could never get much lighter trigger pull out if it. So I left it as it is. Still crisp, but just a bit heavier than the rest. Still kills good , so I’m ok.

    Thanks for the info dudes , good stuff!

    Hippie
     
  12. kevinlg

    kevinlg Well-Known Member

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    Hip......

    The weight screw and over-travel screw adjustments are/should be completely independent of one another.

    That is.....unless I've completely misconstrued your post. :)

    I usually set the weight at about 3 to 3.5 pounds....with no firing pin falls for rough handling.
    Then I set the over-travel for smooth vertical travel of the trigger housing sear(bolt out, and pushing down on sear).......WHILE the trigger lever is under a 3 to 3.5 pound pull.
    This should result in slight lateral play in the trigger lever......with the bolt in a de-cocked/fired condition.

    Hope this helps.
     
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  13. Old Hippie

    Old Hippie Formerly known as bloorooster

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    No Sir , not at all!
    If there is any misconstruing here, it’s probably me, in my explanation.
    So , if I understand correctly, I can adjust the trigger weight alone with one screw and had no need to touch the other small screw (E) that my forefathers warned me to leave alone?

    Also..pushing down on the sear? This is interesting, can you explain this on more of an old hippie level?


    Hippie
     
    Last edited: Jul 30, 2021
  14. paulsonconstruction

    paulsonconstruction Sako-addicted

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    Correct. Misadjustment of the overtravel (backlash) screw can cause the trigger sear engagement problems. It's better to have more overtravel than needed than not enough. Like your Grandpa said, if you don't know what a screw does or how it works, LEAVE IT ALONE!
     
  15. tilleyman

    tilleyman Well-Known Member

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    While that's generally good advice, in my L579 pretty much all parts of the bolt and trigger have been fiddled with... the bolt cocking piece had been filed down in an attempt to adjust sear engagement vs via the upper set screw, which was nearly flush with the top of the trigger housing!
    So I need to start afresh...

    Here's a more detailed 3D exploded view and parts list for the Sako No 4 trigger... I referenced the original part numbers incl the missing two #30 #31.
    May be useful for SCC members?

    Sako No 4 Trigger.PNG
     

    Attached Files:

    Last edited: Aug 1, 2021
  16. deersako

    deersako Well-Known Member

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    Great work Tilleyman.
     
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  17. kevinlg

    kevinlg Well-Known Member

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    Hip.......

    Yes......the weight screw is normally adjusted before the over-travel screw. This is assuming that the over-travel screw has NOT been previously set too tight to the trigger lever.
    I try to keep in mind that used rifles are exactly that.....USED...........and in some cases ABUSED. So let the buyer/new owner beware.
    Heck......many of the old #4 triggers don't even have provision for an over-travel screw adjustment.

    Also....pushing down on the trigger housing sliding sear, is my own method/additional check of my #4 trigger over-travel settings.
    If I recall correctly.....the old school method is to slowly tighten the over-travel screw until the trigger "fails to fire". Then.....while holding "normal" trigger pressure....back out the over-travel screw until "fire". Then back the over-travel screw out an additional 1/8th to 1/4th turn.

    At the end of the day......as others have said.....if in ANY doubt.......take it to a qualified gunsmith.
     
  18. icebear

    icebear Sako-addicted

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    This thread is an example of the best of what this forum is about. You have people on three continents sharing their expertise to help a fellow member with a problem. Bravo!

    Just to add a bit of personal experience to the mix, of all the Sakos I have worked on over the past 20-odd years, I have only twice had to take a Sako trigger apart, and only once did I ever have to touch the sear adjustment. A couple of years ago I had an L61R that the trigger and safety were malfunctioning. The trigger mechanism turned out to be full of dried-up, sticky gunk that was probably lubricant 50 years ago. I had to take the trigger assembly completely apart to get it clean. I never touched the sear adjustment screw, and the gun worked like new when I got it back together. The only time I ever had to mess with the sear adjustment was on a gun that had obviously been worked on by some Bubba who didn't understand how the thing worked. That one I had to clean, inspect, and put back together, starting over from scratch on the adjustments. That one took me a while, but fortunately Bubba didn't use a grinder on it, so with great care I was able to restore it to safe operation.

    The moral of the story, and of my own experience with Sako triggers, is that Paulson is dead right. The only reason to touch the sear adjustment is that somebody else screwed it up.
     
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