Diana 27 rebuild  

  RSS

EdS
 EdS
(@eds)
Joined: 2 years ago
Posts: 26
2019-07-05 18:17:19  

i finally decided it was time to rebuild my Diana (hy score) 27 when it was only  300fps in .22 on the chrony.  This is a 1971 gun and upon opening its clear it's never been rebuilt. Anyway, disassembling the gun was easier than I thought, except for one hitch, when trying to remove the piston seal the bolt with a screwdriver it  sheared off in the piston.  I have a Vortek synthetic conversion seal to put on once I extract the broken bolt, just need to get the right size extractor.  My main question is about the mainspring,  I was going to see if anyone here has used one of the square section Merlin XL springs ARH has for these and if so how it worked out.  Debating one of the Merlin springs or just a stock replacement from chambers.


Quote
JiminPGH
(@jiminpgh)
Joined: 2 years ago
Posts: 293
2019-07-05 19:24:29  

Merlin is just about ideal for a Diana 27.  Super smooth cocking and firing.  Just get an accurate wire thickness and coil count of the original spring.  Multiply those together to get the factory stack height when fully compressed.  Do the same for the Merlin, and cut it to fit.  I'm a big fan of his Merlin spring, and have used it very successfully in several vintage spring guns.

BTW, if it were me, I'd shy away from a synthetic seal conversion.  Well-worn leather sealed guns tend to have a use-polished mirror finish inside the compression tube.  Synthetic seals are prone to stiction unless the ID is LIGHTLY cross-hatched with a brake cylinder hone.  Without it, there's no place for lubrication to live.  Cross-hatching is a tricky thing.  Too much and the tube is ruined.  Don't ask me how I learned this.  I have a couple of factory 27 leather seal assemblies with spacers and screws.  I'd be happy to send you one if you're interested.  Send me a PM.

The Merlin spring is definitely the way to go, the synthetic seal, not so much IMHO.


ReplyQuote
EdS
 EdS
(@eds)
Joined: 2 years ago
Posts: 26
2019-07-05 20:07:44  

Thanks for the info on the Merlin, sounds like the spring to use!  I had debated sticking with the leather seal, and may just put it back on once I get the broken bolt out.  Does it make any sense to do any conditioning of the old leather such as a light sanding or just leave as is and soak in oil?


ReplyQuote
JiminPGH
(@jiminpgh)
Joined: 2 years ago
Posts: 293
2019-07-05 20:33:45  

Leather seals can actually last a lifetime, maybe more.  I have a Haenel III from the 1930s that still shoots strong with its original piston seal.  A little bit of pure silicone oil is probably all it needs.  A few drops on your fingers, then rub it in to make the seal pliable.  Soaking will likely lead to dieseling for a while.

These older guns were actually remarkably engineered to be almost maintenance-free.  Hard to understand, and hard to resist the temptation to over-maintain.  Best way to keep a leather seal piston gun shooting properly is to shoot it regularly.  You know you've got it right when you see a slight golden haze in the barrel after each shot.  Too much oil will lead to too much dieseling.  You want a little, but not a lot.

Good luck. A D27 is well worth the effort!


Cvan thanked
ReplyQuote
DavidEnoch
(@davidenoch)
Joined: 2 years ago
Posts: 259
2019-07-06 17:37:42  

I would use the original spring.  Old Diana springs last as long as leather seals.

David Enoch


ReplyQuote
EdS
 EdS
(@eds)
Joined: 2 years ago
Posts: 26
2019-07-06 21:40:01  

Since the gun is shooting with such low power and I know the breech seal is good I am going to try the original leather piston seal and the Merlin spring first and see how that works.  The old spring has some cant and I think that may be the reason for the low power as the piston seal was pretty well oiled.


ReplyQuote
T-Higgs
(@t-higgs)
Joined: 2 years ago
Posts: 47
2019-07-07 08:25:05  

EDS,

ive not worked on a 27 but have a 25D apart right now. If the pistons are similar, the screw that broke was staked by a horizontal pin. I hear they can be a bear to remove but doable. R7 Maccari spring are very nice in the 25! Again, I’ve never fettled a 27. 

Report back with your findings. 

Shoot long enough and you’ll have a one hole group...


ReplyQuote
EdS
 EdS
(@eds)
Joined: 2 years ago
Posts: 26
2019-07-07 11:36:54  

T-Higgs, that staked screw explains why it broke when I tried to remove it in first place. I assumed pin was to hold outer portion of piston onto the inner stem.  When I tried to remove the broken portion of the bolt with an extractor the extractor broke off in the hole.  Fortunately the bolt and extractor piece broke deep enough down the threaded hole that I can still thread a smaller bolt on with the seal.  I should have the Merlin spring mid week and will report back on the results.


ReplyQuote
T-Higgs
(@t-higgs)
Joined: 2 years ago
Posts: 47
2019-07-07 15:12:23  

B83D73F6 D7F9 41D0 BC83 E476A2A22FB3

quick pic for reference. 

Shoot long enough and you’ll have a one hole group...


ReplyQuote
EdS
 EdS
(@eds)
Joined: 2 years ago
Posts: 26
2019-07-11 16:23:19  

Installed the new Merlin XL spring today with the original leather piston seal.  Ran it over the chrony and still shooting low 200s with .22 Hobby pellets.  I have to conclude that the problem here is the piston seal since I have a new spring and a well sealed breech.  Gonna disassemble it again tommorow and try the Vortek synthetic seal conversion I have and see if that makes a difference.  


ReplyQuote
EdS
 EdS
(@eds)
Joined: 2 years ago
Posts: 26
2019-07-11 17:18:13  

I ran about 40 pellets through it just to be sure, and although had a few odd shots at @495fps with some Superdomes, generally it shot 220-225 fps with either domes or Hobby pellets.  Hopefully after I change out the seal tomorrow will see some improvement.  Then onto my next seal problem gun, an AA Mistral with a loose O-ring seal that's shooting @7ftlb.


ReplyQuote
JiminPGH
(@jiminpgh)
Joined: 2 years ago
Posts: 293
2019-07-11 19:46:12  

Maybe I'm missing something, but have you tried the tissue test to determine if your breech seal is holding?  FWIW, I still have a couple of factory-new 27 leather piston seal assemblies.  PM me if you're interested.


Cvan thanked
ReplyQuote
EdS
 EdS
(@eds)
Joined: 2 years ago
Posts: 26
2019-07-11 23:51:01  

Yeah, did the tissue test with no movement of the tissue, I will try the synthetic seal and if that doesn't work may take you up on the leather piston seal assembly!


ReplyQuote
T-Higgs
(@t-higgs)
Joined: 2 years ago
Posts: 47
2019-07-12 12:25:49  

That’s a bummer EdS, sure sounds like a piston seal problem to me. I soaked this 25d’s leather seal for several days and with the Maccari R7 spring it delivering 350-358ish FPS with 14ish grain pellets. It’s a little jumpy though. Probably because it’s such a light rifle. ? Three ball trigger is a cumbersome  contraption to reinstall. 🙃

Shoot long enough and you’ll have a one hole group...


ReplyQuote
EdS
 EdS
(@eds)
Joined: 2 years ago
Posts: 26
2019-07-13 11:36:35  

I replaced the leather piston seal with a Vortek synthetic seal, reassembled with the Merlin XL spring and finally getting some normal velocities,  averaging 520fps with hobbies in .22, so just over 7ftlb which seems right for this gun.  


ReplyQuote

Please Login or Register