Fixing a stripped stock lug on a Disco or other Crosman gun

[lloyd-ss]

This is for Mustang Mike who has no kind words for how easy these things strip out.

A lot of folks have trouble with the stock lug on the Disco and similar Crosman guns stripping threads.  These are the little 8-32 threads and sometimes the threads strip on the lug, so you get a new lug, and then it strips the old threads in the tube.

Here is a solution I use, I don’t know if it has  been presented by somebody else, but here it is anyway. You can do this with regular hand power tools if you are a little bit handy.

This is a “no turning back” fix because we are changing the 8-32 stripped threads to the next larger 10-32 size. You lose some interchangeability, but it is fairly permanent fix.

Step 1  is to modify the lug.  Clamp the part in a vise, or chuck it up in a lathe, and using a 5/32 (.156) drill bit, drill from the ¼-20 tapped end of the lug until the 8-32 piece falls off. There isn’t much metal in the bottom of the hole and the 8-32 piece will pop off quickly.  Then from the same end, tap through the hole you just drilled with a 10-32 tap.


Step 2,  is to make the new 10-32 stud.  Starting with a good quality 10-32  Phillips head screw, turn or grind the head down until it just barely fits into the ¼-20 hole on the lug.  With a #1 phillips head screw driver, thread the screw in and check it’s length.  You can sometimes make it about 1/16 inch longer than OEM length.  Grind it to the right length.


Step 3, Apply a little permanent Loctite to the threads up near the head of the screw.  Use the red, or grade AV or 680, but not the blue (unless that is all you have.)


Step 4, Thread the screw into the lug tight, but don’t strip it.  IMPORTANT – use a little strip of paper towel to remove ALL excess Loctite from the threads on the stud and in the hole. If you don’t do it right now, later on you might pay the price when you try and disassemble your airgun. 


Step 5, Here is the old and the new.  Check the thread length. A little longer than stock is usually OK, but check to make sure it doesn't bottom out in the tube.
Looks just like it was made in a factory, only better, LOL.


Step 6, Now that you have the lug all fixed up, you can tap the tube out to 10-32.  Make sure the hole is tapped in straight.  Use whatever method you are comfortable with to keep chips out of the tube and to makes sure you don’t leaves burrs inside the tube. You can tap the hole without first using a tap drill. Just let the new 10-32 tap follow the old threads in the hole.


Step 7, You’ll have to drill out the hole in the trigger assembly to about 13/64 (.203) to accept the bigger 10-32 screw. the trigger assy will still work fine other guns.


Step 8, Put it all together and that’s it!   Do not over-tighten, but if you do, and things start spinning without tightening (or loosening) , that little bit of Phillips head recess in the bottom of the lug will help you to tighten or loosen the lug.


I hope this helps somebody salvage some damaged threads and get their Disco back I operation.
Lloyd-ss

[Sqrl Klr]

Boy that rifle sure does look familiar.

Thank you much for the fix Lloyd. Very appreciated. I'm sure Mike and many others will be grateful as well. I'll remember to not tighten the screw so tight from now on and to also put pressure against the stock pushing it against the action when tightening the screw from now on to prevent it from stripping again.

[lloyd-ss]

Gil,
Yes, it ought to look familiar.       Also, Mike had complained about stripping a bunch of those, and, ...shame on me..., I thought it was just Mike being ham-fisted about it. But then i had a few instances of it too and I normally just don't do that sort of thing.  When you have the opportunity to tighten a 8-32 screw with a 7/16 wrench, it is easy for problems to crop up.
Lloyd-ss

[Sqrl Klr]

Well a contributing factor in my case is that I usually tighten the screw with a electric screwdriver. Even though it doesn't tighten with as much max force as I can by hand it still doesn't allow for any feel by hand either to be able to sense when it's tight enough. I also didn't know these guns had that issue nor did it act like it was stripping when tightening. So now I know it was tightening more than needed where I will no longer use it to tighten it securely, but just for turning the screw down near it's end where I'll tighten it manually.

[MustangMike]

SWEET, i swear if i had stripped another one i was going to cry.. seriously i have like 5 or 9 of those stock lugs laying around.


ham fisted huh ? nope not this guy, the first time it happened yes it was my fault but the other times i swear it was like barely tight and then that dread sudden feeling of no resistance when ur tightening something down.

[Sqrl Klr]

Mike he raped me with a $40 charge for that and tapping the hole for it so I doubt you'll get it cheap. lol

Just kidding of course and gladly paying for the fix.

[lloyd-ss]

Mike he raped me with a $40 charge for that and tapping the hole for it so I doubt you'll get it cheap. lol

Just kidding of course and gladly paying for the fix.

  Oh darn, that's right !  I forgot the R&D charges!  LOL

[Kemosabe]

Most excellent tip Lloyd, thanks for sharing!!!

[Sqrl Klr]

Oh darn, that's right !  I forgot the R&D charges!  LOL

Doh! I stepped in it now. Lloyd this clip of Yosimite Sam sounds just like what you'd say next.

http://www.megawavs.com/play.aspx?id=1313

[lloyd-ss]

Oh darn, that's right !  I forgot the R&D charges!  LOL

Doh! I stepped in it now. Lloyd this clip of Yosimite Sam sounds just like what you'd say next.
!
http://www.megawavs.com/play.aspx?id=1313

Gil,
All alone in my shop and I laughed out loud.  Several times!        Very funny!  I can picture that big bushy mustache right now.
Gotta luv it!
Lloyd-ss

[lloyd-ss]

Most excellent tip Lloyd, thanks for sharing!!!

Thanks Kemosabe (I've got the mental image!),
I think if a poll were taken, that would be up there in "Disco - the weak links." LOL
I had previously thought about making one from scratch, but this seemed like an easier way to get a good sturdy thread, and I honestly think that somebody who is good with an electric drill and a bench grinder, could make the same fix.

I do a similar thing to get rid of that hateful little 4-48 screw with the .050 Allen socket that is supposed to hold the breech to the air tube.  I tap the tube out to 6-32, and then take a 6-32 socket head cap screw and turn the head down so that it fits in the original counterbore in the breech.
Lloyd-ss

[gene_sc]

Great stuff Lloyd. Glad you posted the pics and fix. I have had to do that same fix several times on the disco tubes. Got me a good tap and drill first time it happened..
The harder  fix is on the breech side of the tube...

Thanks for sharing
Gene

[Sqrl Klr]

I do a similar thing to get rid of that hateful little 4-48 screw with the .050 Allen socket that is supposed to hold the breech to the air tube.  I tap the tube out to 6-32, and then take a 6-32 socket head cap screw and turn the head down so that it fits in the original counterbore in the breech.

So glad you did that with mine too, although I don't think it was on the verge of stripping like the stock screw hole was......yet anyway.

Good that Sam clip got you some laughs as well. I always liked him when I watched Loony Tunes as a kid so I guess he stuck with me where I remember him at times all these years later.

[MichaelM]

a very nice and elegant solution like always Lloyd!

it could be considered a "might as well do" preventitive procedure as well just like the 6-32 breech screw fix which I am a big fan of

[willbird]

Looks very nice, if I had to guess I'd say they make that part from 12L14 hex stock, which is not very strong once it gets turned down so small then threaded, and the soft material ends up giving way then ruining the tube threads :-).

Bill

[MultimediaMan]

Slightly Off-Topic: I'm see Socketing-Headed Valve Retainer Screws. What size and SKU are these. I read bits and pieces that the screw head diameter is modified a bit, but I've not run into specifics.

[lloyd-ss]

Slightly Off-Topic: I'm see Socketing-Headed Valve Retainer Screws. What size and SKU are these. I read bits and pieces that the screw head diameter is modified a bit, but I've not run into specifics.

Those valve screws are High Strength Low Profile Socket Head Cap Screws with a 10-32 thread.  The standard screws are 8-32 x 3/16 long pan head and I don't know what strength they are.

Using the 10-32 HSLPSHCS helps fix the weak link in the pressure containment of the Discovery.  It is a necessary safety improvement for anybody who might accidentally overfill a Discovery past the rated 2,000 psi. 

Unfortunately, converting to the 10-32 screws is a bit of a pain.  First, you have to go up to the 10-32 size to get a head size big enough to fill the hole in the tube.  But the shortest the 10-32 screws come in is 1/4", so you have to grind 1/16" off the length.  Then you need a 10-32 bottoming tap to tap the hole in the valve out because you want to thread it as deep as possible without breaking out into the throat of the valve.
But I do know of at least one person who just drills the holes in the valve all the way thru into the throat and taps them 10-32, and then uses the 1/4" long screws installed with blue Loctite.  If you think about it, there is no reason that shouldn't work just fine, and it might be even a little stronger than the blind holes and 3/16" long screws.  Any leakage up around the Loctited screw threads would be insignificant compared to what is leaking out past the valve stem during firing.
The screws are from McMaster     92220A171    $7.31 for 25 of the 10-32 x 1/4
Lloyd

[MultimediaMan]

Thank you!

In summary, the OD of the Screwhead will need to be turned-down to fit the Air Tube retaining holes, and the threaded portion shortened to 3/16". The valve body screw holes will need to be enlarged to #10-32 size to a depth of 3/16" with an appropriate drill and Plug Tap and Bottoming Tap (or simply drilled-through if you are comfortable with that).

At the risk of inciting a riot, I would tend to agree with the notion that enlarging the holes by drilling them through may be crime against precision machining, but it is easier to make a better-quality threaded hole. There is no question in my mind that an "air seal" downstream of the valve seat is a moot point. Unless the threads are really loose, any air which might escape via blow-by wouldn't have much time to do so; air pressure creep along the thread "crowns and valleys" path takes time - the air pressure difference (and the pellet) are long-gone before it would be noticed as a problem. Anecdotally, my father once had rebarrelling job come in because of a "drill-through". The customer had a friend who installed a set of scope bases on the rifle the previous week. Unfortunately he had inadvertently drilled the rearmost receiver screw hole for the front scope base through not only the receiver, but all the way through the barrel into the chamber! After his first range session, the customer was a little puzzled that his fired .22-250 cases all had a very clean #32 drill-sized hole in the side when he got home to reload them. Amazingly, the #6-48 (with 1/4" of an inch of threads bearing into the metal) held against the ~50000 PSI chamber pressure for 20 firings. IIRC, there was quite a bit of brass welded/impacted into the bottom of screw, but the scope base screw came out without much complaint.   

It seems to me that if you did drill them through, you might still need the bottoming tap because of how limited the space is in the valve throat.     

Thanks for the info: I got them ordered.

[lloyd-ss]

You've got it correct except that the new 10-32 heads will fit the existing holes in the tube perfectly.

Funny story, except I bet your father didn't think it was too funny at the time. 
Lloyd

[brzryder]

Nice fix at $5.13 each they can run into some coin