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mark 4 disassembly

This is a discussion on mark 4 disassembly within the Ruger Rimfires forums, part of the Pistol & Revolver Forum category; The cross pin that holds the bolt stop pin & mainspring housing in my Mark4 keeps working it's way out every 100 rounds or so. ...


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Old April 17th, 2017, 03:14 PM   #1
 
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mark 4 disassembly

The cross pin that holds the bolt stop pin & mainspring housing in my Mark4 keeps working it's way out every 100 rounds or so. (it's the rear cross pin with 2 grooves in it)

I can feel a little resistance to pushing the pin in so there is some retaining spring tension on the cross pin grooves but it doesn't feel like enough.

I want to take that cross pin, bolt stop pin, & takedown button out to see if I can add a bit more tension to the pin retaining spring but don't want to end up with major reassembly problems.

Has anyone had the rear part of the Mark4 apart yet? If so will I have any reassembly issues.

Any info on that pin continually coming out would also be appreciated.



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Old April 17th, 2017, 07:26 PM   #2
 
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Your retaining spring should have plenty of tension already.

I suspect the pin has been installed incorrectly. The arms of the spring should be under the pin, pushing up against it. If they are over the pin, the tension will be just as you describe and the pin will walk out during use.

I would slowly push the pin with a small punch until I could see how the first spring arm is positioned. If it's wrong, I would continue pushing just until the second arm is free (leaving the pin in the frame). Then use the punch to push the second arm down and slide the pin in over it. Continue pushing the pin until it is at the first arm. Then push the first arm down with the punch and finish inserting the pin until it's flush with the frame. You should feel both arms snap into the pin grooves.

I hope this helps.
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Old April 18th, 2017, 10:35 AM   #3
 
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Originally Posted by TestEngineer View Post
Your retaining spring should have plenty of tension already.

I suspect the pin has been installed incorrectly. The arms of the spring should be under the pin, pushing up against it. If they are over the pin, the tension will be just as you describe and the pin will walk out during use.

I would slowly push the pin with a small punch until I could see how the first spring arm is positioned. If it's wrong, I would continue pushing just until the second arm is free (leaving the pin in the frame). Then use the punch to push the second arm down and slide the pin in over it. Continue pushing the pin until it is at the first arm. Then push the first arm down with the punch and finish inserting the pin until it's flush with the frame. You should feel both arms snap into the pin grooves.


Afternoon TestEngineer

I did check the spring position yesterday by sliding the pin partially out each side. I found it where it is supposed to be (under the pin)

But I didn't see a lot of spring protrusion into the pin hole so it looked to me like it just doesn't have enough upward tension.

I was kind of hoping that someone has had that rear takedown button & slide stop pin apart as I want to remove the spring & bend/retention it.

In any case, lacking any information on taking the rear apart (actually putting it back together as I'm sure that I can get it apart OK) today I slid the pin partially out again then used a very small eye glasses screwdriver to pry the spring legs up reaching in through the pin holes.

I'm not sure how much if any actual spring tension I added but it is a starting point. If the pin now stays put I guess I managed to add tension to spring's pin retaining legs. (it's a work in progress now)
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Old April 18th, 2017, 11:11 AM   #4
 
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The pin holds the mainspring housing, takedown latch, and boltstop pin together, AND holds them inside the frame on top of that spring.

I would suggest you invest in making a slave pin the same diameter as the main pin, but shorter by 2 frame thicknesses. By driving the slave pin in to replace the main pin, you should be able to lift all the parts out as a single assembly. This would give you access to the spring you are interested in stretching, and make reassembly a snap.

Good Luck.
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Old April 18th, 2017, 12:31 PM   #5
 
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Originally Posted by TestEngineer View Post
The pin holds the mainspring housing, takedown latch, and boltstop pin together, AND holds them inside the frame on top of that spring.

I would suggest you invest in making a slave pin the same diameter as the main pin, but shorter by 2 frame thicknesses. By driving the slave pin in to replace the main pin, you should be able to lift all the parts out as a single assembly. This would give you access to the spring you are interested in stretching, and make reassembly a snap.

Good Luck.
Afternoon TestEngineer

So basically I can take it apart piece by piece then reassemble on my bench using a short slave pin, then slide the whole enchilada back in place on top of the spring, then use the factory cross pin to push the slave pin through?

What about the takedown button?

It looks like the takedown button will have to go in as a separate operation as it kind of keys into the frame so won't the slave pin in place prevent removal & re-assembly of the takedown button?

I need to understand this better before removing parts & pieces.
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Old April 18th, 2017, 06:23 PM   #6
 
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Afternoon TestEngineer

So basically I can take it apart piece by piece then reassemble on my bench using a short slave pin, then slide the whole enchilada back in place on top of the spring, then use the factory cross pin to push the slave pin through?

What about the takedown button?

It looks like the takedown button will have to go in as a separate operation as it kind of keys into the frame so won't the slave pin in place prevent removal & re-assembly of the takedown button?

I need to understand this better before removing parts & pieces.
So, look at the "exploded" diagram in your manual. The "button"
(#28) is held onto the MSH (#24) by the main pin (#29). If you disassemble without a slave pin, the dual button springs (#27) will tend to launch all the parts in different directions as soon as your punch is pulled clear of the notch the bolt stop pin sits in.

If you want to disassemble without a slave pin, then I suggest you disassemble with the frame wrapped in a towel to catch the flying parts. No flying parts with the slave pin installed before hand.

If you have all the parts, then yes, you can reassemble on your bench with the slave pin and install the whole enchilada as a single unit. The takedown button will be part of this single unit. It is keyed to the MSH - not to the frame.
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