by Tom Gaylord
Writing as B.B. Pelletier

Part 1
Part 2
Part 3
Part 4

Diana 45
Diana 45 is a large breakbarrel spring rifle.

This report covers:

• Remove the barrel
• Barrel off!
• Remove the piston
• Disassembly is complete
• One last look

We have a lot to cover today, so let’s get right to it. We left the Diana 45 with the mainspring out of the gun at the end of yesterday’s report. The only thing left in the disassembly is to remove the piston. Do not disassemble a gun if you’re not 100% certain you can put it back together again in safe working condition!

Remove the barrel
The piston will not come out of the gun until the cocking link that connects it to the underside of the barrel (for cocking) is removed. To do that, you must first separate the barrel from the spring tube. That step is easy on some breakbarrels, but not so easy with this 45. On most breakbarrels, you remove the pivot bolt from the action forks and the barrel separates from the spring tube. The Diana 45 has another step; and unless you follow it, the barrel will never come off the gun.

I unscrewed the pivot bolt with a Phillips screwdriver. The nut on the other side stayed in place and allowed the bolt to back out. With the bolt out, I could see the star lock washers that are on either side of the pivot bolt hole.

Diana 45 pivot bolt out
The pivot bolt and nut are out, and you can see the star lockwasher still in the hole. With this bolt removed, the barrels on most guns will come out of the action forks (at the end of the spring tube), but not the Diana 45 barrel. There’s still one more thing to do.

The barrel still won’t separate from the action fork. Something is holding it in place. When you remove the star washer, you see a bushing that acts as a bearing for the pivot joint. The pivot bolt passes through this bushing, and it’s the bushing that takes the full load when the gun is cocked. This bushing drives out of the baseblock with little resistance.

Diana 45 pivot bushing
Under the star washer, we find the barrel pivot bushing. This also has to come out before the barrel comes out of the action fork.

After I drove the bushing out of the baseblock, all the parts that hold the barrel in the spring tube action forks are out of the gun. It’s quite a list. They include the pivot bolt, the pivot bolt nut, two star washers and the pivot bushing that acts as a bearing when the rifle is cocked.

Diana 45 pivot parts
All the parts that hold the barrel to the action. The pivot bushing that acts as a bearing is the part that was unexpected.

The pivot bushing drives out easily, yet it fits the pivot joint hole very tight. This will be a part that gets moly grease when the rifle is assembled. The pivot bolt by itself doesn’t really bear much of the force when the rifle is cocked, but I’ll put moly grease on it, as well, just for good measure.

Barrel off!
With the bushing out, the barrel slips out of the action forks. At this point, the cocking link will probably disconnect from the piston by itself, but I’ll come back to that in a moment. For now, let’s examine the sides of the baseblock, which is the flat block that holds the barrel.

Each side of the baseblock has its own unique pivot washer. These are asymmetric metal washers that fit into specially machined cutouts in the baseblock. If this is the first time you’ve seen a breakbarrel rifle taken apart, these may not seem strange; but most guns don’t have them. Most guns have either a plain flat washer on either side of the baseblock or nothing at all. Some guns have synthetic flat washers that wear very quickly when handled but will last long enough if the gun never comes apart.

Diana used these asymmetric washers for many years. They have the advantage of not “walking” out of place when the rifle is cocked. Weihrauch uses flat washers that do tend to walk, though they count on the pivot bolt that passes through their centers to stop them. But Weihrauch washers sometimes get chewed up in their center hole from the contact they make with the pivot bolt. Diana washers cannot move this way, so they don’t get damaged.

These washers are wonderful parts that perform a very specialized job, but the question arises: Are they worth the expense? First, the special washers have to be made (each side is different), then the baseblock must be machined on both sides to fit them. And, if you need to buy a washer at some point, only the same side of the washer will fit, because the other side is shaped differently. So, you have specialized parts that do their jobs very well — instead of plain parts that work okay most of the time. Is the extra machining and cost of stocking different parts worth the benefit?

You know the answer. As we move into the future, specialized parts that are not crucial to the operation of anything will be eliminated. An old Russian saying regarding design goes, “Perfection is the enemy of good enough.” And it does make sense. If plain washers will work, why suffer the expense of specialized parts that require extra machining time and parts handling?

Diana 45 left washer
The left pivot washer fits into a specially machined place in the baseblock.

Diana 45 right washer
The right pivot washer is shaped differently than the left one, and its hole is specially machined to fit.

I mentioned the pivot washers because I’ll lubricate them with moly when I put the rifle together again. Be sure you don’t misplace them — because, as you can see, each one is different. Putting them back isn’t difficult because they only fit one side of the baseblock.

Remove the piston
Now, we’ll remove the piston. When the barrel came apart from the spring tube, the cocking link separated from the piston. It was actually attached to a sliding part we’ll call the cocking shoe. Let’s look at that. The cocking shoe slides in a slot in the piston and is the part that pushes the piston back against the mainspring when the rifle’s cocked. The cocking link fits into a slot in the shoe and does the pushing as the barrel’s levered down.

On many guns, the spring tube has a wide spot in its cocking slot where the shoe can be removed, clearing the way for the piston to slide out of the tube. Until the shoe is out, the piston remains captive in the spring tube.

The Diana 45 does not have a wide spot in the spring tube. It also doesn’t have a cutout, where the shoe might be rotated away from the cocking slot. At first glance, there’s no way to remove the shoe from the piston, and therefore no way to remove the piston from the spring tube.

But it has to come out, because the makers were able to get it in. So, we need to find where that shoe has clearance. And it’s in the bottom of the slot it sits in!

The Diana 45 piston has a black metal sleeve that fits inside the piston. It’s very reminiscent of the beer-can tune that blog reader Milan used to talk about. Being black, it looks like part of the piston, but it’s actually a separate part. When it slides out of the back of the piston, it opens a hole that the cocking shoe drops into. Now, the shoe’s clear, and the piston can be removed from the spring tube.

Diana 45 cocking shoe
The cocking shoe (arrow) slides along the slot in the piston and spring tube. When the gun’s cocked, the shoe pushes the piston back until the sear catches the end of the piston.

Diana 45 piston sleeve
The black piston sleeve (arrow) has been backed out of the piston, allowing the cocking shoe to drop inside the piston body and out of the gun.

Diana 45 piston sleeve outside piston
The black piston sleeve and cocking shoe are out of the piston.

The piston now slides out of the spring tube at the back. As predicted, the leather piston seal looks brand new. It would be a shame to waste a fresh seal like this, which has at least 50 more years of hard use ahead of it.

Diana 45 piston seal
The leather piston seal looks brand new. I’ll reuse it when the gun goes back together.

The black piston sleeve looks exactly like Milan was describing in his beer-can tune. The ends are folded-over flaps that a washer rests against inside, and the mainspring presses on the washer then the gun is assembled.

Diana 45 washer in piston sleeve
The black piston sleeve has small flaps that hold the washer inside. The mainspring presses against the washer when the gun is assembled.

Disassembly is complete
The airgun is now taken apart as far as I’m going to go. At this point, the assessment begins. What’s loose and needs to be tightened?

First, I note that the spring guide is a little loose on the mainspring. A new, tighter guide will have to be made. This is deceiving, since the canted section of the spring is at the end that’s on the guide, so it feels tighter than it really is. The bend helps hold the mainspring on the guide by pushing against it. But I’ve seen enough spring guides to know this one is loose.

Next, I note that the black piston sleeve fits tight inside the piston, but the mainspring is loose inside the sleeve. Now, the outside of the spring increases in diameter when the spring is compressed, so this may not be too bad. We have to allow for some growth of the spring when the rifle’s cocked.

I note that the rear of the piston is loose inside the spring tube. Diana relied on the spring guide and the piston sleeve to guide the piston straight, but I think we might benefit by putting some synthetic bearings on the outside rear of the piston.

I’m impressed by all the attention to detail I see in this air rifle. Compared to this 45, an FWB 124 is simple and a bit crude. But I do know that all Diana 45s buzz a bit, so even these overbuilt parts will need to be tightened just a little. My goal is for the rifle to cock smoothly and easily and for the gun to fire with a solid “thunk.” From what I see in this powerplant, that should be achievable.

Everything from this point on depends on the new mainspring that I use to replace the bent spring that came out of the gun. The dimensions of the new spring will drive all those other tolerances mentioned above — so nothing happens until I have that spring in hand. And, no, not even a spring from another Diana 45 would measure exactly the same as this one. It’s physically impossible to manufacture coiled steel springs to the same, exact dimensions. You can only get springs of the same, exact dimensions by sorting them after production. So, whatever spring I use, all the future work I do on this airgun has to key on it.

One last look
I am impressed by the quality I see in this rifle. Until this disassembly, I had no idea Diana ever made a sporting spring gun this complex. I hope the improvements I make will deliver the results I’m looking for.

I don’t care to increase the rifle’s power with this tune. I’m after smoothness, which is what the owner, Johnny Hill, asked for. If I can get that with reasonable power, I’ll be happy.