Wk-180 upper play removal - simple and cheap solution

L

lmar

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I have posted in the past my disdain for the amount of play between the upper and lower receiver.

I created a stepped pin to see how much play I could remove but it turns out the upper hole (single) is slightly bigger than the bottom (double).
Even with the minimal fitting of the pin, there was still movement between the two parts.
Other than reaming the holes to size them correctly ( and ruin the finish) this option did not pan out as expected.

Looking at the back of the receiver I noticed that the bottom slot had a machined countersink around it. The upper projection into this slot did not.
I then wondered if it was possible to fit an o-ring over the upper slot post and have it "partially sit" inside the groove when the two halves were fitted together.

Initial trials with standard plumbing O-rings proved a no-go as the diameter of the o-ring was too thick and didn't allow the upper to seat on the lower.

I then went to my auto parts store and rummaged around their O-ring board near the counter. I found what I think was a (.070) -013 and -014 O-ring (their distributor uses their own number instead of SAE numbers).

REFERENCE - FIND LOCAL SUPPLIER



O-RING INSTALLED



HAPPY RESULTS





The secret is to get an undersized ring which has to be forced over the upper post. The stretching of the ring results in a reduction of the diameter which just fits in the chamfered groove - removing slop between the two halves.

Note - make sure the latch is engaged properly locking the two parts together. The first time I thought it had but a little wiggling to check play resulted in the two halves coming apart.

In order to ensure the two parts fit I placed the long axis of the gun parallel to the floor (2"). I then lowered the butt until it rested on my carpet and supported the barrel with my other hand.
By placing my body weight at the rear of the gun while holding the front by the barrel I was able to easily lever the two parts together so the latch engaged properly. If you have mounted a scope this may be problematic. An alternative method will have to be devised.

End result is minimal play (wiggle instead of a clunk). Fore to aft is still there due to the front pin clearance issue but the side to side play has been reduced considerably.

The automotive ring has the benefit of being able to handle gun oils as well as elevated temperaturess.

Disassembly is still possible without tools (I had to place one thumb over the other - in order to get enough force to disengage take down latch).

The best part was the auto part counterperson gave me the O-rings for free.

Not sure how long my fix will last but at this price replacements every couple of months is no big deal.

Cheers,

L
 
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That seems to add upwards pressure on the upper which was what i was trying to avoid. I think having orings on near the top and bottom of the lug would be better because it uses lateral pressure to tighten up the lug. Any upwards pressure causes torque on the disassembly button, upper receiver, and recoil guide base would wear it out eventually. Time will tell, let me know how it goes.
 
Drift117 said:
That seems to add upwards pressure on the upper which was what i was trying to avoid. I think having orings on near the top and bottom of the lug would be better because it uses lateral pressure to tighten up the lug. Any upwards pressure causes torque on the disassembly button, upper receiver, and recoil guide base would wear it out eventually. Time will tell, let me know how it goes.
Click to expand...

I hear what you are saying. In my view....

Theoretically yes. Practically, no - the o-ring will "squish" long before the metal parts start to wear. I was considering machining a groove in the lug (both top and bottom) to fit a thicker O-ring to accomplish exactly what you suggested.
Alternatively, I was thinking of drilling two partial holes on either side of the lug and then placing a length of round sealing rubber into the holes. Since the material would stick out it would take out the play (easier to drill than to mill a groove around lug circumference).

The added machining vs what I would get in return was deemed too much work. Should I wear out the rifle in my lifetime due to this "fix" I figure top end replacements should be available in a multitude of calibers.

This is not a 1 MOA gun - the purpose of the mod was to get rid of the play which detracted from the "feel" of the rifle. This it does quite nicely. I don't expect it to improve accuracy.

Note - the easiest fix is to modify the G-code to make the lug wider in order to remove the side to side clearance.

My philosophy is based on "this is a utility rifle - treat it as such". YMMV depending on your point of view.

Cheers,

L
 
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lmar said:
I hear what you are saying. In my view....

Theoretically yes. Practically, no - the o-ring will "squish" long before the metal parts start to wear. I was considering machining a groove in the lug (both top and bottom) to fit a thicker O-ring to accomplish exactly what you suggested.
Alternatively, I was thinking of drilling two partial holes on either side of the lug and then placing a length of round sealing rubber into the holes. Since the material would stick out it would take out the play (easier to drill than to mill a groove around lug circumference).

The added machining vs what I would get in return was deemed too much work. Should I wear out the rifle in my lifetime due to this "fix" I figure top end replacements should be available in a multitude of calibers.

This is not a 1 MOA gun - the purpose of the mod was to get rid of the play which detracted from the "feel" of the rifle. This it does quite nicely. I don't expect it to improve accuracy.

Note - the easiest fix is to modify the G-code to make the lug wider in order to remove the side to side clearance.

My philosophy is based on "this is a utility rifle - treat it as such". YMMV depending on your point of view.

Cheers,

L
Click to expand...

I personally like tinkering. XD
 
Mine has never wobbled much at all; if I shake it vigorously while holding onto just the lower (charging handle removed) all I can hear is the slightest "ticking". It does however require some significant force on the takedown button to strip the rifle. It can be so stubborn that I've had to use the back of a pen to get it open when I got tired of jabbing my thumb in that channel.
 
Mine also had some play initially. I sent an email about something else (missing spare screws) to Kodiak and mentioned it. When this thread got posted and Owen from Kodiak saw it he actually sent it to me and said it looked promising. I ended up using a 7/16ID, 9/16OD o-ring and it basically eliminates play without making the takedown button difficult to depress by hand. I've been running it for a while now and I can't recommend it enough. It greatly improves the feel of the rifle.
 
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