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Releasign Threadlocker w/o Wrecking Heat Treat?

I have several Italian .22LR Olympic-style "free pistols" I am repairing for the collegiate pistol team I help coach. These are Pardini PGP-

75's, which are bolt action:

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To set the "headspace" (gap between the bolt face & chamber), they use a hardened eccentric bushing at the base of the bolt handle. It rides in the slot in the action, and rotating the bushing adjusts the headspace. If the headspace is too large, you get unreliable ignition, and/or reduced accuracy.

The bushing position is set at the factory, and clamped with the bolt handle, which screws down on top of the bushing. Both the bolt handle threads and the bushing are treated with some sort of 30 year old Italian threadlocker (maybe even epoxy). I've experimented with a variety of solvents, and acetone & lacquer thinner won't touch it. Methylene chloride (paint stripper) softens it up, and allows cleaning off the exposed threads & loose bushings.

On some pistols, the bushing slips & just needs to be repositioned. On others, the bushing cracks & has to be replaced. Spare parts are very scarce, and we only have a few extra bushings.

I have one pistol where the bushing is OK, but must have slipped during installation. It works OK, but the headspace is well past the nominal upper limit. I got the bolt handle off with a strap wrench, and expected that the bushing had slipped, but it is firmly stuck.

I've had it soaking in paint stripper for a month now, but I suspect the gap between the bushing & the bolt stud is too small to allow enough solvent in to undo the bushing in less than geologic time.

The other approach for dealing with most threadlocker is heat (~ 300F?). I can make a specialized soldering iron tip that I can slip or clamp over the bushing to free it. The iron I currently have is temperature controlled, but at 700F. I could also go & buy a cheap resistive iron and use it with a variac to control the temperature down at a better level.

Thank you for anyone who has stuck with me so far. Here's the question:

I would really like to salvage the bushing. What's the best way to get it off without wrecking the heat treat? It's quite thin (< 0.5mm), and I will be applying heat on the outside to get through to the inside.

The best options I've come up with are:

1) Use my 700 degree iron, with a tip mounted with a small brass block with a hole that is a slip fit over the bushing. If I c*ck the tip at a slight angle to get good thermal contact, I should be able to pull the bushing off as soon as the threadlocker lets go, and then the bushing should fall free from the heat source.

2) By a cheap iron, and make the tip clamp securely onto the bushing. Then use a variac/dimmer to sneak up on the temperature. I have a set of Tempilac sticks that I can use to tell when it has reached certain temperatures. I also have an infrared thermometer, but I don't think it goes hot enough for this. With this approach, I am unlikely to get the bushing much hotter than required to melt the threadlocker, but it will be at that temperature for much longer.

3) Contact Italy and try to get more replacement bushings. That could take months, and is not a sure thing. One reason I want to salvage this one is the spares we obtained earlier may have been the dregs. Some of them are not very eccentric, and many are not a very good fit on the bolt handles.

4) I can certainly continue to leave the bolt soaking in paint stripper. I have other projects to keep myself busy, and if I can repair all the other pistols, the pressure will be off. It doesn't seem to affect the metal, and if I keep it sealed up, I can try to wait it out.

5) Quench after getting it free. Given how hard they are, quenching presumably wouldn't make it much harder. However, it could become more brittle, and likely to crack.

6) Make new bushings. I have no idea how involved this would get. I did a rough hardness test on a cracked one using hardness files, and it was ~ RC60 (which may be why it cracked...). I don't have any experience or equipment to do sophisticated heat treating. I'm assuming that heat treating will probably distort them a bit, and/or mess up the surface finish enough that a light grind would be in order. I can certainly rig up a Dremel as a tool post grinder for that. The big advantage with this is that I can make a bunch. I know of at least one other college team that has even more dead ones than we do.

Other ideas & comments?

Thanks!

Doug White

Reply to
Doug White
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I would need more info on the temperature required to affect the heating treating of the metal. I question whether the heat required to soften the thread blocker is enough to effect the metals heat treatment. But, as I said,I need more info. Mikek

Reply to
amdx

If you have the whole thing off couldn't you just place it in your oven at say 400 deg?

When trying to transfer heat like that I've used solder before. Depending on the solder you know you would be at 600 to 700 deg. Usually those kinda of temps are used for tempering more so than hardening from my understanding, which isn't much on that subject :)

I couldn't get your link to work but I found this with a general search:

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Might help some others visualize your dilemma. I'm guessing it is item

26 on the exploded view page.

Oh and its an interesting gun. Wouldn't mind shooting it a few times ;-)

Reply to
Leon Fisk

I've placed a short piece of fine electronic solder on a part held in the vise and heated it from below with a torch until the solder melted and shrank into a ball.

Reply to
Jim Wilkins

Leon Fisk wrote in news:o8v133$nho$ snipped-for-privacy@dont-email.me:

The link apparently got busted by word wrap. If you splice it together it works fine.

That's the critter.

Shooting "free pistol" is a whole different game from any other sort of pistol shooting. The "free" is because it is relatively free of restrictions. Typical trigger pulls run about an ounce. The grip is set up so that it hangs onto you as much as vice versa. The bore is very low, so the recoil is very staight back into your hand, with very little muzzle flip. Matches are 60 shots at 50 meters over 2 hours. The target is the same one they used when the modern Olympics got going in the late 1800's. No one has ever fired a perfect score.

Unfortunately, they are threatening to remove it from the Olympics, which would be a real shame. Spectating is like watching paint dry unless you are really into subtleties, so it isn't telegenic enough for the modern short attention span of TV audiences.

Doug White

Reply to
Doug White

Well then you need to go talk to some of the female beach volleyball crowd and see if they want to be on the teams. In the same "uniforms" they normally wear. I'd bet the sport would gain viewers....

Reply to
Steve W.

Generally speaking, any substance used as a thread locker would probably soften by the time it reaches, say 200 degrees F. And again, generally speaking, a thread locker probably wouldn't be very soluble in various solvents.

I think my first attempt would be by heating the bolt in boiling water, keep it boiling until you are sure that the bolt actually reaches ~212 degrees.

Another point RC 60 is pretty hard stuff. For a .22 pistol I would suggest that if it is that hard it is probably for something other than strength.

I once converted a bunch of S. American , small ring, Mausers to sporting rifles and as I had to forge the bolt handles I tested both the bolts and the receivers first and found that were in the range of un-heatreated steel, relatively soft. I can't believe that a .22 would have to be harder ;-)

I had a look at the break down drawing of the PDP-75 and if you are talking abut the ring, at the rear of the bolt, that the bolt handle seems to fit through, index 25, the drawing seems show a straight forward sleeve (but it is a pretty vague drawing :-)

Reply to
John B.

John B. wrote in news: snipped-for-privacy@4ax.com:

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Thanks for the feedback.

The bushing/sleeve is hardened because it is what slides in the slot in the action. It's to prevent wear, not for strength. In the exploded diagram, the sleeve is part #26. #25 is the bolt handle, and #27 is the knob that screws onto a stud that stick out of the bolt handle. The eccentric sleeve fits on an unthreaded section at the base of the stud.

The sleeve is about 7.5mm in diameter, and the inner hole is about 6mm, but offset about half a mm from center to produce the required eccentricity.

I could certainly try boiling water, but none of the modern threadlockers I've encountered soften up much at that temperature. The vast majority of Locktite products are rated for use up to at least

300F. I would expect them not to soften until they get even hotter than that.

Doug White

Reply to
Doug White

The original Loctite Blue had a heat range of somewhere in the 200 degree (F) range and your pistols were made in the late 1970's I believe :-) And it is so cheap to try boiling water :-)

Does the exocentric sleeve have any manner of hold it, or turning it, when adjusting the head space? I would think it would require something.

I rebarrelled a number of NRA target pistols at one time or another and the major problem I had was actually too tight headspace and chamber dimensions. Although admittedly NRA target shooting is a bit different than Free Pistol :-)

If it is just an ex centric sleeve I would think that any competent machinist could churn out a bunch in a morning. If you made them out of something like "drill rod" they could easily be hardened and tempered to RC 60

Reply to
John B.

I believe that Loctite states that the temperature limits of Loctite "blue" is -65F to 300F. But a bit more reading shows that this is the "improved" version so it is possible that a pistol assembled 38 years ago might have been assembled with something with lower temperature limits.

Reply to
John B.

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