by Tom Gaylord
Writing as B.B. Pelletier

HW 55SF
HW 55SF.

Part 1
Part 2
Part 3

A history of airguns

This report covers:

  • Barreled action
  • Trigger out
  • The trigger
  • Remove the end cap
  • Remove the piston
  • Extra parts?
  • Piston seal
  • Inspect the parts
  • Put everything back
  • Tighten the pivot bolt
  • Installing the trigger
  • The test
  • Summary

Many readers wanted to look inside the HW55 SF, and today is the day! This is a Weihrauch spring rifle, and it comes apart like most of them. There are a few differences that I will mention as we go. Let’s get started!

Barreled action

The first step after checking to make sure the rifle is not cocked and loaded is to remove the stock. On this rifle that means loosening three screws — one on the underside of the forearm and the two triggerguard screws. The screws can remain in the stock and triggerguard for safekeeping, but the triggerguard is removed from the stock. I’ll have something more to say about this during assembly.

HW 55 sight off
The sight comes off the action.

The next step is to remove the rear sight. That clears the dovetails for attaching the Air Venturi Rail Lock Spring Compressor. That has become a valuable tool for working on spring guns.

Trigger out

The next step is to remove the Rekord trigger. The HW55 has the special target Rekord that doesn’t have a safety, so when the trigger comes out there is no safety and spring to worry about. Just punch out the two pins left to right and the trigger is out.

HW 55 drift pins
Drift out the two pins that hold the trigger. I remove the front pin first and I go from the left side — opposite what this picture shows.

HW 55 pins out
With the pins out the trigger can be lifted out of the action.

The trigger

With the trigger out I can show you how this one differs from a standard Rekord. I’ll do it with pictures.

HW55 piston catch
The front of the piston catch is ground and hand-filed at the factory (arrow) to refine the engagement with the piston rod. A sporting Rekord is rounded at this point, unless someone filed it afterwards.

HW 55 piston catch rear
The rear of the piston catch that’s held by the sear (arrow) is also hand-filed at the factory.

HW 55 trigger return spring
The trigger return spring (arrow) is much lighter than the spring on a sporting Rekord. Hand-fitting the trigger parts makes it possible for this light spring to work.

Remove the end cap

Let’s get back to the rifle. To remove the end cap we unscrew it from the spring tube. I have attached the spring compressor and unscrewed the end cap until the last three threads hold it in the tube. Then the rod on the compressor is run in to hold the end cap and I start slowly unscrewing the cap and the rod in the compressor. When the end cap is out of the spring tube the compressor rod is unscrewed until all tension is off the mainspring.

HW 55 spring relaxed
The mainspring has just relaxed. So, there is almost 3-inches of spring precompression (the spring outside the tube plus the length of the threads) when the rifle is together.

Now the end cap is removed, the compressor is taken off the spring tube and the mainspring and its guide come out of the tube. When they did I found a small amount of grease on the mainspring. It wasn’t moly and it wasn’t lithium. It was some sort of general purpose grease. That tells me whoever tuned this rifle last was probably knowledgeable and conservative. It might have been a dealer.

The mainspring is also straight, so it’s good to put back in the rifle. The guide fits close but somewhat loose. These parts are factory for sure. I cleaned all the grease off the mainspring and rolled it on a flat surface, looking for a wobble. No wobble. As I told you, it is straight.

HW 55 spring out
The mainspring is straight. The medium-viscosity grease is on thin.

Remove the piston

To remove the piston the barrel must come off, so the cocking link can be removed from the piston. That’s done by removing the pivot bolt nut, followed by the pivot bolt.

HW 55 pivot nut off
The pivot nut and washer come off the right side of the gun. The washer is a circular wire that is a replacement from later than the 1968-69 manufacturing date. This rifle has been apart since it left the factory.

HW 55 pivot bolt out
Now the pivot bolt is removed. The barrel can then be removed from the action forks. Once it’s free, the cocking link can be taken out of the piston.

HW 55 barrel out
The barrel is separated from the action forks.

HW 55 slide piston out
Remove the piston by sliding it out the back of the spring tube.

When the piston came out I saw moly grease on the rear, where the piston body is swelled. There was no grease on the piston body forward of this. That tells me the tuner knew what he was doing.

HW 55 piston out
Only the swelled rear of the piston is greased.

Extra parts?

About this time I felt an “extra” part in my hand. Because I have experience with Weihrauchs, I knew it was a piece of the leaf spring that keeps tension on the articulated cocking link, so it doesn’t rattel. The other part of the leaf spring was still held by the forearm screw boss that was still in place. Was this a problem? Wait and see.

HW 55 screw boss
The forearm screw boss (left) and the broken leaf spring were removed.

Piston seal

I was somewhat surprised to see a synthetic piston seal in this gun. I would have thought it would be leather, but 20 years ago it was popular to replace the original leather seals with synthetic seals. At that time many people thought synthetic seals were better. I don’t, and I wish the original leather seal was still in the gun.

It is possible that this seal is original, though I have rebuilt two other HW55s that were a couple years newer than this one and they both had leather seals. The piston had to be changed for the synthetic seal to work, so if this was done is was a deliberate act.

At first glance the piston seal appeared to be ruined. It had a lot of black gunk caked on top and in the parachute groove. But I was able to clean most of the gunk off and what I found was a seal that’s still pliable and ready for more use. Because of that, I will press on and complete the cleaning and overhaul today. I may order a replacement leaf spring, but I will put the rifle back together and use it without the spring.

HW 55 piston seal before
At first glance the piston seal looks ruined.

HW 55 piston seal after
After cleaning the seal; is okay and still pliable.

Inspect the parts

At this point I inspected all the parts, including inside the spring tube. The cylinder is crosshatched well and surprisingly clean. All the parts were in good condition, except for that leaf spring, so the gun is good to go.

Put everything back

I lubed the piston seal with Air Venturi Moly Paste and slid it back into the gun.

HW 55 piston seal lubed
The seal was lubed with a thin coat of moly grease.

I also lubed the swelled back end of the piston with moly. The body of the piston never touches the inside of the spring tube, but the swelled back end and the piston seal both do. That’s where the grease is needed.

HW 55 piston end lubed
The back of the piston is swelled to guide it inside the tube (if it bumps the inside of the tube). That got some moly.

The gun then went together the reverse of coming apart. I don’t like it when people say that, but it’s true. I will discuss the few things you need to watch for, but first, I lubed the mainspring with a good coat of Tune in a Tube grease.

HW 55 mainspring lubed
Mainspring lubed with Tune in a Tube.

Tighten the pivot bolt

I lubed the pivot bolt with moly before inserting it. When you tighten the pivot bolt, remember to get it tight enough to hold the barrel in position after the gun is cocked.

Installing the trigger

When installing a Rekord trigger it helps to cock it first. Do that by pressing down on the back of the piston latch until the sear grabs it.

HW 55 cock trigger
Press down on the back of the piston latch to cock the trigger before installation.

The gun went together smoothly. Just remember when you tighten the triggerguard screws that the rear (smaller) screw is going into a threaded piece of sheetmetal in the trigger body. Don’t tighten it too much! If you strip it a nut can be inserted to hold the screw, but it’s a chore.

The test

After the rifle is together I pulled the trigger because it had been cocked to install. Then I cocked the rifle to load it. Cocking was smooth and this time there was no hesitation in the stroke. Remember that? There was a spike in the cocking effort toward the end of the barrel stroke.

Then I fired it with a pellet. Dead smooth! So smooth that I don’t think I will do anything else to this rifle except retest the velocity and accuracy for you.

Summary

It took me 90 minutes to do everything seen here, including taking a lot more pictures than you see. These older Weihrauch air rifles are so easy to work on!