Crosman Crosman 1720T - Adjustment screws loose?

[SAZ]

For you 1720T owners out there,

Have you ever had either or both of your H.S. adjusting screws back out of adjustment on their own ?

Several times now I've adjusted the 1/8" & 3/16" head H.S. adjustment screws where I want them and then after "some" shooting, anywhere from 20-40 shots most often, one or both of the screws will be 1/4 turn or more counter-clockwise to where I adjusted them.
I can tell when it's happening because the normally very accurate pistol will start shooting poorly. It usually starts shooting a little low I think because of the adjustment screw or screws backing out. I don't think it's ever gone clockwise on me.
It only started doing this a few months ago. I've owned this pistol a few years and it's never done this before. Set it and forget it was how it used to be.

I've taken it apart and checked / cleaned everything but this weirdness keeps happening.

Or, maybe MY screw's come loose.

 

[DARKHORSE1967]

If you’re handy enough you could drill and tap your rear cap vertically.

That is a brass 8-32 set screw so as not to mess up your adjuster’s threads.

I use 2 on mine, the one on top pushes onto the first one to secure it even more:

 

[SAZ]

If you’re handy enough you could drill and tap your rear cap vertically.

That is a brass 8-32 set screw so as not to mess up your adjuster’s threads.

I use 2 on mine, the one on top pushes onto the first one to secure it even more:

Thanks!
That looks like a great fix if I was using that type of external adjuster.
I should have mentioned that I'm just using the factory internal adjustment screws.
Part #34 & #41 in the parts diagram.

I'm thinking that maybe a wrap of teflon tape might be the cure.
Unless it falls off and gets wadded up in something, but if it works it's solved the problem.
If not, it wouldn't take too much to clean up the strips of tape I don't imagine.

I had purchased a product similar to LocTite (but from another company) that was red in color after I saw a couple videos where the guy was using it on scope ring caps on a high powered rifle. You could install and remove screws multiple times without re-applying the product. They were using it on screws that were prone to loosening up under use and vibration. It didn't harden up completely. It remained pliable for multiple uses.
Maybe I'll try it if I can find the tiny little tube and see if that works.

 

[Gwelo]

I’ve had good luck with Vibra Tite. Sounds similar to what you describe.

Vibra-Tite VC-3 Threadmate

www.vibra-tite.com

It also comes in tape form.

Vibra-Tite VC-3 Tape

www.vibra-tite.com

 

[SAZ]

That's the stuff........

 

[DARKHORSE1967]

Saz, your response made me look at mine again, lol!

I do have a PROD and a 17 (one is with a custom AR adapter), but I had to refresh myself (again) as to how I set up mine.

So, I blue-Loctited #41 on both of mine after determining where I wanted them set at; they haven’t budged so far in several years despite Blue being known as anemic compared to Red.

I do have 2 of those 22xx vertical set screw locks on 2 rear caps and was planning to have the same on my PROD/17, but I came up with a solution that required me not to bore holes.

I modified a stainless 3/8-24 button screw (99% sure of the thread size) I bought from Ace H, had the tip shaped in cone to push onto #34 and avert CCW creep.

The O-ring is there to act as lock washer, a tensioner so as not to make the thread length too crucial.

Note: Mine are low power builds.

Don’t mind the color, it’s coated:

 

[Gwelo]

I think the 1720T comes from the factory with some type of thread locker. After a few adjustments it loses its effectiveness and things start moving around. When you had yours apart did you see any signs of thread locker?

Is item 37 in your parts diagram a set screw to lock down item 41?

 

[DARKHORSE1967]

I think the 1720T comes from the factory with some type of thread locker. After a few adjustments it loses its effectiveness and things start moving around. When you had yours apart did you see any signs of thread locker?

Is item 37 in your parts diagram a set screw to lock down item 41?

No, #37 is just a plastic and threadless plug—-and seems to offer no function at all, it not even a tight fit.

You could replace it with a weed whacker nylon of slightly larger diameter for a much tighter fit.

Now that you’ve mentioned it, I scantily recall some threading it for a set screw to immobilize #41.

 

[SAZ]

Thanks for the help guys!

I'm going to go with the Vibra-Tite for now and see how that works.
I want the ability to make minor changes without a lot of hoopla if needed.