A 34 yo. 34

[Denby95]

I like the replacement. I remember seeing your very first pictures and seeing all those screws in the rear sight and just thinking 'hey! happened there?'

[HectorMedina]

God Job, Ilimakko!

I would give the seal the "release force" test.
When you have the gun apart, put the piston inside and use a long tube that can make the stem go into the tube, it does not need to fit tightly, then using a simple kitchen scale, hold the gun with the piston (retracted), and the tube protruding, onto the scale.
Then press little by little.
The piston should start moving with about 1½ # of force.
Too little and you are loosing compression in the most important section of the compression phase. Too much and the seal is "robbing" energy from the shot cycle.

MOST D34's I have tried yield, with mild tunes right at the 12 ft-lbs region, in the HP tunes, they can yield up to 15 ft-lbs in  0.177" and up to 20 ft-lbs in 0.22" with GTO lead free pellets/ 16½ ft-lbs with lead pellets in the 14.3 grs. region.

Cocked/crooked springs will not perform well if the crooked section is at the back try reversing the spring and see if there is a noticeable impact in MV's.

BTW, you CAN straighten a spring, but then put the straightened section at the REAR where the guide will protect the straightness.

Keep up the good work!







HM

[Toxylon]

Hector,

I reckon you missed an 'o' in your header 

I have been taking kitchen scale piston resistance measurements on every gun I tune for a couple of years now, ever since learning first-hand how tight seals rob a couple hundred fps, while loose seals lead to a bunch of other issues. I've been going with the "2 lbs. rule" for calibration (allowing up to 3# on magnum springers), which seems to work fine.

The CAS seal, freshly installed and lubed with a speck of Ultimox, moved in the chamber at a very high, 2.5kg / 5.5 lbs. resistance. Going by the seal diameter and previous experience, I knew this wasn't the whole truth.

For now I can't seem to find my back-of-the-envelope scribblings from a later point, but I remember the piston easing up drastically, the chamber resistance registering well under 2#, but a "close the TP and pull on the piston" test suggesting the seal was doing its job.

I fully suspect the seal isn't working well in this gun. My next step will be sizing an OEM seal and see how it affects the performance; I'd bet a couple of fpe appears from doing just that.

The canting in the Titan is quite evenly distributed along its length, with a bunch  of minor deviations left and right from a straight line. How to straighten them out, I have no idea.

Going by the canting etc., I still think the Titan has been overstressed by the ~20 coil bound cockings altogether. One reason is that, starting from a very springy, muscular beginning, the spring is now really mellow to cock, close to effortless. So, even going with a perfect piston seal, I predict we'll be a couple of fpe under the target. But the proof is in the experiment.

[Toxylon]

Great thread, thanks for sharing. And yes, the D34 loosens screws in a hurry! Link below to a thread that might help. I have flat washers and star washers sitting in a bag on my work bench.

https://www.gatewaytoairguns.org/GTA/index.php?topic=122338.0

I've used Hector's recommendation of Nordloc washers to great success. Just remember they must torque down against metal surface per manufacturer specs, so you need a small flat washer between the stock and nordloc.

I put flat washers under the star washers yesterday, and they were needed: there was stock wood powder coming off with the star washers, or business as usual. Not only for protection, the stock screws also seem to hold a bit better as well, although that may be an effect of the break-in taking effect.

Drew,

Thanks for the Nordloc suggestion! I'll look into them.

The gun sure did clean up esthetically, from getting rid of the Franken-sight.

[uglymike]

I'm still following, nice job on the "rescue rifle". Picture of it now please.

[Toxylon]

There'll be pictures, Mike - good to know I have an appreciative audience!

I took the suspect CAS seal out. Now, after several hundred pellets and a chamber bath in Ultimox, the piston resistance with the seal was really low, around 100 grams or so. So, for the second Diana in a row, the Diana CAS seal is a dud. You can always whittle an oversized seal down, but there's no option for adding material. So, this'll be the first and last CAS seal in my possession.

The CAS seal measured 28.1mm in diameter, which has been a sufficient "overshoot" in some of my 28mm bore guns. I checked the D34 receiver ID: at the rear of the receiver, the inside diameter is 28.55mm!

I know receiver rear doesn't neccessarily have the same ID as the compression chamber, but there's no reason to think, nor indication, that they are that much different in this gun, either. The piston has the same resistance at the rear as in the chamber. Of course, going by the numbers, there should be zero resistance with a 28.1mm seal in a 28.5mm hole. Maybe the piston body itself adds some drag in the push test.

So, I fitted the piston with an Diana OEM 28mm seal, which had a whopping 28.9mm OD. To my surprise, the massively oversized seal, lightly lubed, moved inside the chamber with really quite proper fit, registering around 1000 grams, or 2,2#.

I'm going to break in and test out the gun with this seal as is and go from there. In my 350 Mag, an OEM seal of 28.6mm cut velocity by around 200 fps, even after a thorough breaking in, but it's looking like the 1988 gun has a very different bore, as far as piston seal sizing goes.

[Denby95]

I was curious about the CAS seal sizing so I measured 2 different ones that I had myself. One is from about 6-8 months ago and was removed because I damaged it, and the other is brand new unused, just arrived from an order I made the other week.

One was 28.5 and one was 28.49.

[Toxylon]

I've been checking out those Nord-Lock washers. I would prefer to use a nifty mechanical solution to prevent stock screws from loosening, as opposed to a sticky chemical one (Loc-Tite).

The Nord-Lock washers I've seen for sale are double thickness, on top of being serrated. They look too thick to fit in the shallow counter sinks for the stock screw heads and any possible washers. This especially with Drew's point on needing to fit flat washers under the Nord-Lock ones. This because the Nord-Locks don't work on soft materials, and would likely eat up the stock wood if one tried.

The manufacturer says the Nord-Locks should NOT be combined with a flat washer:

"We do not recommend using a Nord-Lock wedge-locking washer in combination with a plain washer. Serrations on the Nord-Lock washer will grip the bolt head and your plain washer, successfully locking these two together, however this plain washer will not be locked against the contact surface which means it can rotate."

So, how do people use the Nord-Locks on springers? Do the stock screw heads protrude above the stock surface, with all the hardware under them? How do short front stock screws like the ones in my '88 D34 even reach the receiver yoke with triple washers installed? Do the stock screws stay put even with flat washers under the Nord-Locks?

[Denby95]

The new Diana 34 EMS actually comes with them from the factory, and they're fitted against flat washers.

So per Hector's recommendation of them, and seeing that on my 34 EMS, its exactly what I've done. I use a low viscosity cellulose nitrate to harden up the wood (most people use cyanoacrylate) and stick in a flat washer, and then the nordloc on top. I've not had any issue with the thickness of screws sticking out etc and the few times I've removed the stock, you'll hear an audible click of the serrations unlocking as pressure is released. So per what the manufacturer is saying, you're getting around the potential for the flat washer rotating because it is stuck down via adhesive to the wood stock.

[Denby95]

I picked up a few brand new Diana seals from Umarex just out of curiousity. Got near measurements as you just to further validate that Diana OEM seals are quite large.

Word to the wise, don't get ripped off like I did. They charged me 10 bucks shipping for 1.20 in actual shipping costs, and sold me the f-velocity ring instead of the compression seal for my D54. Is any experience with Umarex ever positive?

[Toxylon]

Thanks Drew!

So, "gluing" the smooth washer down does the trick.

You know, I've been wondering about the large size of the Diana OEM seals, but this D34 with an oversized bore shows why they are the way they are. If you have a 28.5mm bore, you better have a piston seal around 29mm in diam. to start with.

The hitch is, unless you know what you have, per individual seal AND gun basis, you may well end up having a seal that cuts velocity by hundreds of fps. That happened with my 350 Mag, and I have heard identical stories from others.

In my 350's case, an OEM seal sized down to 28.4mm did the trick. The same seal in my 34 would've been undersized.

[Arch_E]

Super informative thread!

Thanks for the meticulous notes throughout this process.

Archie

[Toxylon]

Much appreciated, Archie!

[uglymike]

I picked up a few brand new Diana seals from Umarex just out of curiousity. Got near measurements as you just to further validate that Diana OEM seals are quite large.

Word to the wise, don't get ripped off like I did. They charged me 10 bucks shipping for 1.20 in actual shipping costs, and sold me the f-velocity ring instead of the compression seal for my D54. Is any experience with Umarex ever positive?

Positive experience....with Umarex? I dealt with them several times years ago and I'll never do business with them again.

[HectorMedina]

I picked up a few brand new Diana seals from Umarex just out of curiousity. Got near measurements as you just to further validate that Diana OEM seals are quite large.

Word to the wise, don't get ripped off like I did. They charged me 10 bucks shipping for 1.20 in actual shipping costs, and sold me the f-velocity ring instead of the compression seal for my D54. Is any experience with Umarex ever positive?

Sorry you got that, Drew.

I would talk to the supervisor and explain that you got the wrong seal and that they need to send you what you paid for, and that if they want the wrong part back, they need to send you a shipping label and an MRA.

It's annoying to pay for Shipping AND Handling a lot more of what actual shipping costs, but that is a US habit and the dislike of that habit was what created the monster that Amazon is . . .

Keep us posted.





HM

[Toxylon]

After replacing the sorry CAS seal with a Diana OEM seal, I put around 100 pellets through the D34 to break in the new seal.

A chrono session today gave the following results, averaged out:


R10 Match 8.2 gr.:

274.8 m/s  /  902 fps

20.1 J  /  14.8 fpe


FTT 4.52 / 8.64 gr.:

259.7 m/s   /   852 fps

18.9 J   /   13.9 fpe


Sniper Medium 8.49 gr.:

262.6 m/s   /  862 fps

19.0 J   /   14.0 fpe


Daystate Heavy 10.25 gr.:

229.1 m/s   /   752 fps

17.4 J   /   12.8 fpe


Polymag 8.02 gr.:

271.8 m/s   /   892 fps

19.2 J    /   14.2 fpe


Exact 4.52 gr.  / 8.44 gr.:

259.4 m/s   /   851 fps

18.4 J   /   13.5 fpe

....

So, replacing the piston seal (while doing nothing else) increased muzzle velocities from 26.7 to 42.8 m/s, or from 88 to 140 fps! Muzzle energies increased accordingly, by up to 5.8 J, or 4.3 fpe.

The biggest gainers were the R10's and the FTT's. The low-release-pressure JSB's were a bit mellower. The JSB Daystate Heavies had much lower KE's than any of the mid-weight pellets, telling how this setup works best at around 8.5 gr.'s.

The Sniper Mediums varied in velocities pretty wildly, expressing the quality issues these otherwise high-performance pellets have, or had.

Polymags had the best shot cycle and one of the highest KE's.



The 34 year-old 34 performs now at a 100 % healthy level, and that feels really good! Hector had it right (as usual) in that the piston seal was the issue. I sure wouldn't have guessed that an almost 1.0mm oversized seal would be just the right medicine for this gun.

I'll start the accuracy testing with FTT's and Exacts, with some Polymags thrown in.

One issue I need to deal with first is the rear sight, which refuses to stay put with the normal stresses of shooting.

[cjtamu]

Glad you got it sorted. The more I shoot mine the more I it. I like it so much my wife is threatening to buy me a custom stock for it for Christmas. I might just let her  . Thanks for the thread, some useful info for other 34 owners in here.

[Toxylon]

nm

[Denby95]

Whats the plan with the rear sight? Try to find an OEM type replacement? Swap for something else like the ever popular williams diopters?

[Toxylon]

Thanks, Chris!

Here are some pics as promised: she's come a long way from the 30-year sentence in a damp, dark cell.