by Tom Gaylord
Writing as B.B. Pelletier

Diana 27S
Diana 27S.

Part 1
Part 2
Part 3

A history of airguns

This report covers:

  • Trepidation
  • Disassembly
  • Anti-beartrap mechanism
  • Pictures!
  • Secret washer
  • Remove the trigger?
  • The rest of the disassembly
  • Cleaning
  • Lubrication and assembly
  • Hit the wall
  • Frustration
  • The solution
  • The final solution
  • Denny was a pattern maker
  • The irony!
  • One more thing
  • Summary

Today I do something different. I show you a tuneup that is not complete. I do that because the monster has been vanquished and I will be able to get the Diana 27S back together to report on the performance after a cleaning and a lube tune. Here we go.

Trepidation

When I began this job a week ago I had trepidation because of the anti-beartrap mechanism Diana put in this model. I have stripped other springers with anti-beartraps before and I’ve always been successful, but their presence complicates the rest of the powerplant quite a bit — especially the trigger.

I also knew that the 27S probably had the trigger from the Diana 35 instead of the trigger that’s found in the 27. They are similar, except the 35 trigger has a more powerful spring pushing the inner ball bearing cage. And that particular spring also has a guide rod that the 27 spring does not have. 

So, I took a lot of pictures as I worked. It turned out those pictures saved the day, though not in the way you might think. Explanations are coming.

Disassembly

First the stock is removed to get to the barreled action. Since the 27S has an articulated cocking link it has an additional stock screw on the bottom of the forearm. I was prepared to see that screwed into a steel bridge that the link passes through — to keep it from buckling. But there was no bridge. The screw just has a rounded end for the link to slide on and the absence of a mark on the link told me it had never touched that screw. The stock keeps the link from buckling!

Diana 27S stock screw
That screw under the forearm was supposed to screw into a steel bridge that the cocking link passed through. But it didn’t.

Diana 27S  stock screw inside
The forearm stock screw attaches to this threaded bushing inside the wooden forearm. The tip is rounded to allow the cocking link to slide over it, but the link never touched it! The wood of the stock keeps the link aligned.

Diana 27S  stock screw detail
The end of the forearm stock screw is rounded to allow the cocking link to slide over it freely, but the link has not touched it yet.

Anti-beartrap mechanism

Setting the stock aside, I now examined the anti-beartrap mechanism.

Diana 27S  anti-beartrap
This picture shows the long sliding plate of the anti-beartrap mechanism. Two springs pull it into the trigger when the cocking link moves far enough to permit it.

Diana 27S  anti-beartrap 2
This is the anti-beartrap mechanism interfacing with the trigger assembly. The two springs pull the sliding plate into the trigger when a notch in the trigger blade permits it to enter.

At this point I thought I was home free. This mechanism is simple and looks straightforward. But I was about to encounter a problem!

Pictures!

Because this is the first time I have seen this mechanism, I took a great many pictures of it. And they saved the day several times. The large bolt in the center of things is where the forward triggerguard screw attaches. It also limits the movement of all the anti-beartrap parts to a short range of movement that you will see in a moment. But that wasn’t the most important thing. I will get to that in a bit.

Diana 27S  anti-beartrap 3
The bolt in the center of the anti-beartrap (arrow) limits the movement of the rest of the parts.

Shop Benjamin Rifles

Secret washer

Here is the first surprise this mechanism gave me. After I disassembled it completely a small thin washer remained on the spring tube. Where it came from I had no idea, but when I reviewed all my pictures of the mechanism, taken while disassembling it, I found it! It took me quite a while (45 minutes of trying the parts various ways and then searching through the photos) to determine where this small washer belongs.

Diana 27S  anti-beartrap washer
The arrow points to the small thin washer in the anti-beartrap mechanism that I found after disassembly. Only a portion shows, but it’s enough to determine which layer the washer sits in.

Diana 27S anti-beartrap washer out
There is the tiny thin washer, hiding under the trigger blade. Apparently it is shy. Next to the trigger are the crosspin and the stout trigger spring that gave me so much trouble!

Remove the trigger?

At this point in the disassembly I decided to disassemble the trigger assembly from the spring tube. I believed that was necessary, though I now know different. It meant I also had to remove the anti-beartrap mechanism — also unnecessary. But I did it. At least you get to see the parts that are in the mechanism.

Diana 27S  trigger mechanism
The trigger mechanism with the anti-beartrap still connected. This picture was very helpful later, as well.

Diana 27S  anti-beartrap apart
The bolt has been removed, giving access to all the parts. I have also disconnected both anti-beartrap springs.

I don’t show all the beartrap parts apart, but they are basically several sliding plates of steel that can be seen stacked in the picture of the assembled trigger above that was taken before disassembly.

The rest of the disassembly

Now the barreled action went into the mainspring compressor for complete disassembly. With the beartrap apart and the trigger out of the rifle the two side pins that restrain the internal trigger parts (the black and silver cages and the ball bearings that are in the black cage) can be removed. Just press in on the black trigger cage with the compressor to take tension off the two pins and they fall right out. Then back off the compressor and the mainspring relaxes. You can then remove the spring guide and the mainspring.

At this point all other spring rifles require removal of the barrel to disconnect the cocking link from the piston. Then the piston can be removed. I did remove the barrel, and only later discovered that the two-piece articulated cocking link would allow me to remove the piston without first removing the barrel. However, taking the barrel off allowed me to lubricate the pivot bolt and the to pivot washers with moly grease, so the effort was not wasted. But this was another difference the Diana 27S showed me.

Cleaning

I cleaned all the parts with denatured alcohol. To get inside the spring tube I used a long dowel with paper towel wrapped around the end. The inside of the spring tube was surprisingly clean and did not appear to have ever been taken apart. I will let reader Carel address that, since the gun was his before I received it.

The other parts were also very clean for the 40 or so years this airgun has been around. The mainspring is not perfectly straight, but it’s close enough that I don’t think a replacement is needed. 

Lubrication and assembly

I lubed the leather piston seal and the front and rear of the piston body, as well as the central piston rod, with moly paste grease. Then I lubed the mainspring with a light coating of Tune In A Tube grease. I also used TIAT to stick the three ball bearings inside the black cage for assembly. Even when the cage fell to the concrete floor the balls remained tightly inside. Now for assembly.

Hit the wall

And assembly was where I hit the wall. To this point in the report I had spent perhaps 90 minutes on a job that usually takes me 30. I was taking my time to understand the anti-beartrap mechanism completely. And I missed the biggest challenge of all — the trigger spring!

Frustration

I took the remainder of that day and two hours into the next day trying to put the crosspin and the trigger spring back in the rifle! I could get it partway, but never all the way in. I started with brute force and when I didn’t have enough of that I used wood clamps. Let me show you what challenged me so much.

Diana 27S  spring tube
This is where the trigger assembly goes. That small bump (arrow) holds one end of the trigger spring in place. As you can see, it is coated with TIAT to hold the spring.

Diana 27S  spring standing
The trigger spring is standing up on the small bump. It’s held by TIAT. The trigger assembly has to come down and connect to the other end of the spring.

Diana 27S  trigger interior
The underside of the trigger assembly has another bump (arrow) that has to fit inside the trigger spring on its other side.

You might think that keeping the powerful trigger spring in place was a problem. But it wasn’t! Tune In A Tube is so tacky that it held the spring through all I did. The problem was pressing the trigger assembly down far enough so the crosspin could pass through both side and hold it. That was what I struggled with for the rest of the time.

The solution

The solution was in two parts. First I had to find a way to use the small wood clamps to press the trigger assembly down against the force of the spring and still not slip off the greasy spring tube and trigger assembly. I am now estimating that spring has 60-80 pounds of force. It’s way out of proportion with its size!

I played with clamping positions for hours, almost getting it before the clamp shot off and I had to start over. Then the lightbulb went off and I put the clamp where it could not slip, no matter what. It still slipped but now it was slipping because the force of the spring was bending and twisting its jaws. That made it easier for me to control.

It was now Day Three of my saga, but I knew I was going to succeed this time. It only took me 10 minutes and a few tries before I succeeded in getting the crosspin 3/4 on the way through.

Diana 27 crosspin almost
The crosspin (arrow) is almost through the trigger assembly and the two anchor points on the spring tube.

The final solution

The second part of the solution was to ask my neighbor, Denny to tap the crosspin through the trigger assembly while I held it in place with a more powerful wood clamp. I had read somewhere that many hands make light work or men should learn to ask for help or something like that!

Anyway, I showed Denny what I was trying to do and then he tapped the pin though as I held the trigger assembly down and in line with the wood clamp. It worked the first time in less than ten seconds.

Denny was a pattern maker

Then Denny looked at the job and told me I probably needed to get a Kant Twist clamp for tight work like this. You see — Denny was a pattern maker. That’s a guy who makes jigs, fixtures and patterns for production work. He worked last in the aviation industry, making patterns for the B2 bomber.

I looked Kant Twist clamps up at Granger and saw a wide variety of cantilever clamps. They are indeed the tools needed for a job like this. Better still — DON’T TAKE THE TRIGGER OUT IN THE FIRST PLACE!

So why did I take the trigger out? Because I thought I had to! The 27S trigger is very similar to the trigger that’s in the Diana 35 — with one important difference. The Diana 35 trigger pin passes through the spring tube of the rifle, where the 27S trigger pin is below the tube. Let’s see.

Diana 35 trigger pin
The crosspin that holds the Diana 35 trigger assembly passes through the spring tube (yellow arrow) as well and has to be removed to get the piston out. The blue arrow points to another powerful trigger spring in the 35 trigger that was somehow easier to work with last year than this 27S spring has been.

Diana 27S crosspin
As you can see, the Diana 27S trigger crosspin (arrows) hangs below the spring tube. That allows the piston to come out without the trigger being removed. And, unless my eyes deceive me, the wire in this spring is thicker than the wire in the 35 trigger spring.

The irony!

The irony of this misadventure is this — Diana designed the 27S to be easily maintained. The trigger doesn’t have to come out to remove the piston, nor does the anti-beartrap need to be removed. Even the barrel can be left on the gun! I didn’t know any of that up front so I did all of it and increased my work a lot. Of course I did get to examine, clean and lube all the parts, which is what you want to do in a tune, so I would have done most of it anyway. But I wouldn’t have removed the trigger! 

This report is now a detailed set of instructions for the next brave soul to follow. That’s why I have taken the time to spell out all the details.

One more thing

When I disassembled the rifle I noticed that the trigger in the 27S resembles the Diana 35 trigger in many respects. The spring that pushes the black cage holding the three ball bearings is very strong, just like the one in the 35 trigger. It’s not like the regular Diana 27 trigger that’s weaker. The 35 cage spring has a short steel spring guide, while the 27 trigger does not. This 27S did not seem to have that guide when I disassembled the rifle, or if it was there I never saw it and it has now gone to the same place as all my missing socks.

The truth is, I found a photo that shows conclusively that there was no spring guide in that spring to begin with. I tried to assemble the action without that guide, but that powerful cage spring just bunched up. When I removed it, it was kinked. I don’t want to assemble the rifle wrong, so I ordered a new spring and guide from T.W. Chambers and will wait for them to arrive to complete this job. I don’t want to do this job again, so it’s worth doing it right this time!

Diana 27S cage spring
There is no steel spring guide in the black cage spring in the Diana 27. It’s end would be in front of the end of the spring. Look at the same part in the Diana 35 above. Photo was taken before disassembly.

Summary

This has been a bit of a horror story of what can happen when you disassemble a spring-piston air rifle. This is perhaps the second time in the last 25 years that I have been so challenged — which is my way of telling you it usually isn’t like this. Please don’t be put off by this tale, but glean what you can from what I did and how it turned out.

Oh, and guys — please be open to asking someone to help you when you need a third hand. I mean — honestly! Pride goeth before a fall!