That's the gun, and this is the place :-)! Got my parts from JM, got the old girl torn down, and then left it in pieces for two days. Just too dog tired with all the other stuff I've been doing to tackle it. This is how it looked torn down.
Decided to go all out on this one, so in addition to the JM tune kit, I ordered both an Apex and a Tesla seal, as well as a set of button. I've buttoned the piston of a couple of other springers with these and have been very pleased with the results.
The original spring is on the top, the JM kit on the bottom. A little hard to tell in the pic, but the JM kit includes both a top and bottom guide, and comes with a sample of heavy tar, which I ended up using. What you can't see in the pic is that the Diana spring had a pretty good kink in it. Specs on the factory spring are .122" wire dia., 33 coils, .807" OD, and approx. 11" over all length. BTW, this should be the same as the Diana 34. Like the Gamo CFX and Shadow 1000, they share the same power plant. The JM spring is slightly different, .128 wire, only 30 coils, and a slight increase in OD. Over all length is maybe 1/4" less.
For those that are interested, here's a shot of my spring compressor. Not fancy, but it works and I was able to put it together from stuff I had on hand when I needed it. It's opened up a fair number of rifles, and with the exception of the Diana's, has had plenty of reach. Diana seems to put a lot of preload on their springs, which makes taking one apart a bit of a challenge at times :=).
Okay, the prep work is out of the way, time to get too it. I was kind of alarmed when I first opened this thing up. I've been inside at least a 1/2 doz. springers, and this is the first one that had metal shavings EVERYWHERE! I couldn't tell where it was coming from until I pulled the piston, and there it was. A fairly extensive galled area right in front of the trigger assembly in the top of the chamber, where the rear of the piston rides. I knew it felt rough when I cocked it, but I didn't realize it was eating itself. I couldn't get a shot of the galling inside the chamber, but you can see the filings on the piston.
Fortunately, the piston was fine, and the area that was galled isn't a sealing area, so I'm hoping that polishing it out and buttoning the piston will prevent any recurrence. It's certainly made a difference in the way it cocks, but that's getting ahead of myself :-).
The rest of this tune was pretty straight forward, deburring, cleaning, polishing and degreasing the rear of the piston for the buttons. For those that have never used these, it couldn't be simpler. You glue them on with super glue and sand down to fit, no more metal to metal contact. According to JM they last a very long time, and at $6 for 6, I think it's well worth the slight extra time and effort. I honed out the area where the gall was, but left the compression area alone, it looked fine. In retrospect, that might have been a mistake, but I can always take it apart again.
In addition to the two different piston seals, I also have a full complement of JM lubes on hand, including something new called Euro lube. This resulted in a short case of smorgasbord starvation, in that I couldn't make up my mind what combination of stuff to use. I finally decided to just stick to basics, and went with the Apex seal and regular old heavy tar and moly. Reassembly was easy, other than the long spring preload, and the rifle went back together in short order. And no left over parts :-)!
So here's where I tell you it shoots like a PCP and the velocity is in the 900's. NOT! I felt the velocity was a little low on this rifle when I got it, JSB Expresses were only averaging 780 fps or so. I was hoping to get the velocity up in the mid 800's, but that didn't happen. In fact, it didn't change AT ALL! Actually not as big a deal as it sounds, this is freshly post tune, less than 50 pellets on the tune. I think I've heard a 10% increase in velocity as things break in isn't unheard of, although 5% is probably more common. Even at only 5%, that'll get me into the low 800's, and I can certainly live with that. I must have gotten some lube ahead of the piston seal, it's dieseling a little bit, but again, I expect that to clear up in short order. As to the rest of it, I'd have to say it's an unqualified success. The cocking stroke is now smooth as silk and silent, cocking force is noticeably less, despite the slightly heavier spring. I can only attribute that to the lube and buttons. The real surprise is the shot cycle. It's VERY quick, with absolutely no torque, twang or buzz. Reminds me of the gas ram I put in my old CFX. This is now the only springer I've been able to watch the pellet hit the target, it's that smooth.
At this point, about the only thing I didn't do was put new breech seals in it. This is a known weak area in these rifles due to the pop up loading gate being a very long transfer port with two seals in it. I haven't tested mine, but it seems okay, although I will be checking it out. Thanks to Marvin, who was good enough to send extras with the rifle. But for now, I'm just going to shoot it, let everything break in and see how it does.
One final note for those of you that own Diana (RWS) rifles. It's common knowledge in the air gun community that Diana rifles ship with very little lubrication. I discovered it when I got my first Diana, a .22 350. But I'd never really followed the logic to its obvious conclusion, which is, if you don't deal with it fairly quickly, you're going to do some damage. I don't know how much Marvin shot this thing, but from the condition it was in, it couldn't have been that much. So my suggestion would be that if you're thinking about buying a Diana, at least order a lube kit from JM and build yourself a spring compressor. And do it sooner rather than later. And if you're not comfortable tearing one down, then factor in the cost of a professional tune when you start shopping. A 34 is considered a good deal at around $200, but does that still hold if you bump it to $350 with a tune? Just something to keep in mind. Later.
Dave
