Diana Diana mod 5 worn pivot

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borne2fly

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Nov 27, 2023
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Santa Clara
My old Diana 5 has gradually worn over the years and now shows a noticeable barrel “tip up”. This is severe enough that it shoots high even with the rear sight all the way down. I’m thinking this is due to wear and slop in the barrel hinge. The hinge bolt seems ok, so I guess the hole has worn out-of-round. Fair enough, the thing is over 50 years old.
Is there any way to adjust this? If not, would the fix be to overbore the hole and press in a bushing?
 
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Agreed, a bushing is the best solution. Execution is key, of course...do your best to get the bushing centered on the original pivot axis. Just plunging into the obround hole with a drill bit will put it on a new axis. Milling it would be best if you have the means and motivation. Or a bit of ingenuity and caveman tools can get the job done. For example, start by carefully filing the obround into a round, biasing it slightly away from the location of the wear. That will form the basis for keeping the drill bit centered for drilling the final hole to accept the bushing. Or sometimes you can get away with simply filing or grinding a slight bevel at the edge of the hole on the side where you want the drill bit to take a bigger bite.
 
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nervoustrig said:
Agreed, a bushing is the best solution. Execution is key, of course...do your best to get the bushing centered on the original pivot axis. Just plunging into the obround hole with a drill bit will put it on a new axis. Milling it would be best if you have the means and motivation. Or a bit of ingenuity and caveman tools can get the job done. For example, start by carefully filing the obround into a round, biasing it slightly away from the location of the wear. That will form the basis for keeping the drill bit centered for drilling the final hole to accept the bushing. Or sometimes you can get away with simply filing or grinding a slight bevel at the edge of the hole on the side where you want the drill bit to take a bigger bite.
Click to expand...
Yeah, this sounds like a job for the Bridgeport. I suspect most of the wear in the hole is toward the rear and downward, where it would experience the maximum force from cocking the spring. That leaves the top and front of the hole relatively true. I can indicated from those. I dread jobs like this … it’s not like I can just go get a new barrel if I mess it up 😳
 
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so, you haven't taken it apart to look
the barrel angle is controlled by the breech seal and the shims behind the Oring
if the Oring has been smash over time and there are no shims, replacing and adding could fix it but to just guess is a crazy why to go about it
so is this a Model 5 that has the plastic grip frame
 
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marflow 777 said:
so, you haven't taken it apart to look
the barrel angle is controlled by the breech seal and the shims behind the Oring
if the Oring has been smash over time and there are no shims, replacing and adding could fix it but to just guess is a crazy why to go about it
so is this a Model 5 that has the plastic grip frame
Click to expand...
Yes, the model 5 with the plastic grip.
I never noticed any shims behind the o-ring. Are you saying that the barrel angle depends on the amount of “crush” of the o-ring rather than a proper mechanical stop? I’d worry about repeatability if so.
But I did notice a slight play in the barrel (not side to side, that was perfect) which would suggest a worn pivot. I haven’t mic’d the hole yet for out-of-round.
 
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Yes, the model 5 with the plastic grip.
I never noticed any shims behind the o-ring. Are you saying that the barrel angle depends on the amount of “crush” of the o-ring rather than a proper mechanical stop? I’d worry about repeatability if so.
But I did notice a slight play in the barrel (not side to side, that was perfect) which would suggest a worn pivot. I haven’t mic’d the hole yet for out-of-round.
 
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well the model 5-5g-6g-6m-10 all use shims behind the Oring
i have seen as many as 4 to 0
if the rear sight was on the breech block it would not matter but being on the rear of the tube it does
now has the 5 and 6's had problems with elevation, that would be a big Yes
i don't believe have read about a worn breech bolt before and or a breech that is damaged
the model 5 has a linkage pin that come right out vs the 5G that has to be pounded out
the reason is the 5G pin has splines and was press in
the barrel would not have any side movement as it has bearing washers on both side and the barrel and washers is a very tight fit in the tube end
if for some reason the washers were not installed that could be a problem and has caused damage
i don't believe the breech bolt would found, as Waffencenter gotha doesn't not list it and any replacement could be a challenge
so the old fix for the barrel shim is dental floss
you take some floss and make several loops and install behind the Oring
the Oring is a 2.5mm x 7mm 70 or 90 dura
the shims are 0.10mm thick
it take very little to change POI while adjusting your breech seal
sound hard to believe but it is the way it works
 
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marflow 777 said:
well the model 5-5g-6g-6m-10 all use shims behind the Oring
i have seen as many as 4 to 0
if the rear sight was on the breech block it would not matter but being on the rear of the tube it does
now has the 5 and 6's had problems with elevation, that would be a big Yes
i don't believe have read about a worn breech bolt before and or a breech that is damaged
the model 5 has a linkage pin that come right out vs the 5G that has to be pounded out
the reason is the 5G pin has splines and was press in
the barrel would not have any side movement as it has bearing washers on both side and the barrel and washers is a very tight fit in the tube end
if for some reason the washers were not installed that could be a problem and has caused damage
i don't believe the breech bolt would found, as Waffencenter gotha doesn't not list it and any replacement could be a challenge
so the old fix for the barrel shim is dental floss
you take some floss and make several loops and install behind the Oring
the Oring is a 2.5mm x 7mm 70 or 90 dura
the shims are 0.10mm thick
it take very little to change POI while adjusting your breech seal
sound hard to believe but it is the way it works
Click to expand...
Thanks! Great info!
I’ll definitely give that a try. I like the dental floss trick but I’ll try punching out a few brass shims first.
Are those Orings still available anywhere?
 
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well nylon is a but hard but it could
if you look at the seal shim total you are looking at from 2.5mm to 2.9 mm
i have a Diana P5 it was later called the 5G mag but the breech doesn't close enough and it is a metal to metal fit
i found a front sight to correct the problem and the real fix is to remove my barrel and remove material and test the problem is the barrel linkage hardware is different and one of the hardest assembles to reassemble
my point is the pistols were never prefect and the shims were the quick fix
if the Dura of the material was in the 80-90 range there is not reason it would not work and how to adjust how proud it sits could be adjusted
now i have no idea if your breech cross screw is damaged or the seal needs shimming
i have model 5's here and i could remove the screw and measure it for you and taking the barrel of isn't hard
set screw out cross screw out and i little wiggling clean inspect and see
but shimming is easy to test
https://www.google.com/search?q=met...xuAeSBsIHBzAuMi44LjHIBzA&sclient=gws-wiz-serp
 
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marflow 777 said:
well nylon is a but hard but it could
if you look at the seal shim total you are looking at from 2.5mm to 2.9 mm
i have a Diana P5 it was later called the 5G mag but the breech doesn't close enough and it is a metal to metal fit
i found a front sight to correct the problem and the real fix is to remove my barrel and remove material and test the problem is the barrel linkage hardware is different and one of the hardest assembles to reassemble
my point is the pistols were never prefect and the shims were the quick fix
if the Dura of the material was in the 80-90 range there is not reason it would not work and how to adjust how proud it sits could be adjusted
now i have no idea if your breech cross screw is damaged or the seal needs shimming
i have model 5's here and i could remove the screw and measure it for you and taking the barrel of isn't hard
set screw out cross screw out and i little wiggling clean inspect and see
but shimming is easy to test
https://www.google.com/search?q=met...xuAeSBsIHBzAuMi44LjHIBzA&sclient=gws-wiz-serp
Click to expand...
Hmmm, this might be the excuse I need to get a 3D printer …. 🤔
The more I think about this, the more ways I see to improve on the original design. But it’s way too easy to fall into those sorts of rabbit holes so I’m going to resist that for now and go with the Oring + shims.
I still don’t see how anything closing against a rubber Oring can be reliably repeatable … seems like the compressibility of the Oring would introduce slight differences every time the breech was closed (depending how gently, or not, you closed it each time)? And wouldn’t that effect the point of aim?
The pivot screw looks good. I got a few extras years ago just in case, but they seem pretty tough.
I hear what you’re saying about your breech closing metal to metal. Mine does that too. I would actually prefer such a solid mechanical lockup, but only if the barrel remained properly aligned. I have a Predom Lucznik that’s almost a metal to metal lockup … no Oring at all but some sort of extremely thin fibrous gasket (leather?) on the breech. That stuff seems to resist any further compression and lasts forever. I’d try it on my Mod 5 if I could ever find out what it was.

Thank you again for all the info, and the leads for Oring sources 👍.
 
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we assume that if Diana made it, it has to be right
the fact is over the many years break barrel pistols do not have a long list
lets change gears for a second
Diana rifle all have the sights on the breech and barrel end and they shoot fine and the reason is the sights are on the same plane
add a scope and the scope will run out of elevation adjustment and the reason it is a droop barrel
so here we are having the same problem in reverse, the rear sight is all the way down and the barrel is too high
the 90 dura Orings are tough enough to hold their shape and hell you will have a bag of them
there are no other break barrel pistols that i know of that use shims just the Diana's
you will solve this and be back shooting bulls and then you need a model 6 and then a model 10 and they will open your eys to a all new shooting experience
 
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marflow 777 said:
we assume that if Diana made it, it has to be right
the fact is over the many years break barrel pistols do not have a long list
lets change gears for a second
Diana rifle all have the sights on the breech and barrel end and they shoot fine and the reason is the sights are on the same plane
add a scope and the scope will run out of elevation adjustment and the reason it is a droop barrel
so here we are having the same problem in reverse, the rear sight is all the way down and the barrel is too high
the 90 dura Orings are tough enough to hold their shape and hell you will have a bag of them
there are no other break barrel pistols that i know of that use shims just the Diana's
you will solve this and be back shooting bulls and then you need a model 6 and then a model 10 and they will open your eys to a all new shooting experience
Click to expand...
The mod 5 was my first airgun. I got it back in 1972 and have been a Diana fan ever since. Got a mod 48 a few years ago and will probably keep that forever as well.
 
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Marflow knows his stuff! Start with the breech seal.

O-rings are cheaper than dirt online, you can buy a bunch of different sizes and materials for pocket change. Sizes are designated by the internal diameter and material thickness (example: a "3.0mm x 2.0mm" O-ring is 7mm in overall diameter). When I'm buying them I measure the existing seal as closely as I can, then order sizes that match, plus some a hair bigger and smaller, and see what works.

Diana guns of that era make liberal use of thin metal shims in many places. The gun should still have its original ones under the breech seal which may be fine if you drop in the proper size O-ring. It's easy to make shims too, you can use thin plastic sheet stock from a hobby shop or similar materials.
 
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MDriskill said:
Marflow knows his stuff! Start with the breech seal.

O-rings are cheaper than dirt online, you can buy a bunch of different sizes and materials for pocket change. Sizes are designated by the internal diameter and material thickness (example: a "3.0mm x 2.0mm" O-ring is 7mm in overall diameter). When I'm buying them I measure the existing seal as closely as I can, then order sizes that match, plus some a hair bigger and smaller, and see what works.

Diana guns of that era make liberal use of thin metal shims in many places. The gun should still have its original ones under the breech seal which may be fine if you drop in the proper size O-ring. It's easy to make shims too, you can use thin plastic sheet stock from a hobby shop or similar materials.
Click to expand...
I ordered a variety of those Orings online and certainly some of them should fit. Definitely looking forward to getting my old mod 5 back in shape
 
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the one thing you have to keep, in mind is all metric Oring state the CS and ID
so in this case 2.5mm x 2 + 7mm ID and that give you 12mmOD
now if you take a 3.0mm and do the same thing you OD changes
now if change to inch sizes, the size you need falls in between a 108 and 109 one OD is too small and the other is too big
but again with the shins you can change the CS from 2.5mm nominal to 2.9mm and the ID and OD stay the same
now i said nominal and the reason is all Oring of the same size might not be the same size
the CS could be + or -
in most cases it will never make a difference but in this case where we are talking about 0.10mm it could
and to understand that better my paper i use in my printer is 0.10mm and that is 39 thousands
 
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marflow 777 said:
the one thing you have to keep, in mind is all metric Oring state the CS and ID
so in this case 2.5mm x 2 + 7mm ID and that give you 12mmOD
now if you take a 3.0mm and do the same thing you OD changes
now if change to inch sizes, the size you need falls in between a 108 and 109 one OD is too small and the other is too big
but again with the shins you can change the CS from 2.5mm nominal to 2.9mm and the ID and OD stay the same
now i said nominal and the reason is all Oring of the same size might not be the same size
the CS could be + or -
in most cases it will never make a difference but in this case where we are talking about 0.10mm it could
and to understand that better my paper i use in my printer is 0.10mm and that is 39 thousands
Click to expand...
Yes, that confused me a little at first because I was looking for an OD and an ID.
When all else fails I read the instructions :).
 
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New shims installed 👍. Shot a bunch of rounds to adjust the sights and now it’s good as new! No more metal-to-metal contact upon closing the breech, and no more barrel tip-up. I was afraid that the compression of the Oring would vary each time I closed the breech but no, it’s actually quite consistent.
The barrel doesn’t sit flush with the piston tube anymore. It presents a tiny step-up at the breech junction, and now I remember that step being there when I bought it new back in 1972. So I reckon that’s the way it’s suppose to be.
 
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