John B. wrote in
:
On Sun, 26 Feb 2017 15:26:07 GMT, Doug White
wrote:
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:
http://picturearchive.gunauction.com...2.jpg_thumbnai
l 1.jpg
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 a
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 cock 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
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 :-)
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