Need info on odd (to me) HW55 piston I received for a rebuild.



Author Topic: Need info on odd (to me) HW55 piston I received for a rebuild.  (Read 1519 times)

Offline nced

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In the past I've oring sealed a couple HW55 pistons, however the piston I received today from "down under" is the strangest piston I've ever seen and I need a bit of help with this one.

Here are a couple pics..........





These pics show both cocking shoe slots, the wrecked leather piston seal, and how the piston cap is threaded into the piston shell and doweled.

The first oddity about this early leather sealed piston is the fact that it has a cocking shoe slot on BOTH sides of the piston.

Second oddity is that the piston shell is threaded and an aluminum piston head was screwed into the piston shell then pinned with an offcenter dowel.

Third oddity is that the milled cocking shoe slots on each side of the piston cut through the threaded end of the piston shell allowing the spreading of the shell where threaded.

Fourth oddity is the fact that the steel piston shell on one side where the retaining dowell is positioned is actually cracked and the piston head is starting to separate from the shell. I personally don't see why the piston head would be "pulling away" from the shell because it seems that the compression pressure of the shot cycle would be pushing TOGETHER the cap and shell, not SEPARATING it!

Fifth oddity is that it seems the cocking shoe was "jamming into" the aluminum piston cap where the milled slot was cut into the cap because the cocking shoe has deformed the aluminum on the side where the cocking shoe slid as shown in the pic with the two permanent marker arrows.

Anywhoo......as mentioned I've worked with/restored a couple HW55 pistons and neither had cocking shoe slots on both sides of the piston. Does anyone here have any insights into this particular piston?   

  • Rougemont, NC

airnutz

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Re: Need info on odd (to me) HW55 piston I received for a rebuild.
« Reply #1 on: July 06, 2012, 04:06:05 PM »
Hello nced,

Now I'm no Expert by any means.  I opened up a HW55S just a month or so back, and I remember it having two slots also, because I had to remove the spring again because the shoe was 180 off.   ;D

The leather seal looks as if it has been hitting a spot weld on the inside of the piston.  I had this on an old  Diana 35.  Could it be that someone previously tried to repair the piston by installing a new front, hence the strange threaded part you mention?

Just some food for thoughts.

Greetings, Robert

Offline nced

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Re: Need info on odd (to me) HW55 piston I received for a rebuild.
« Reply #2 on: July 06, 2012, 11:58:28 PM »
Greetings Robert from warm and balmy North Carolina!

I've disassembled the old HW55 piston and here is a pic of the parts.........



It seems that HW first threaded the aluminum piston cap and steel piston shell, screwed them together, then rolled a crimp into the end of the piston shell to retain the piston cap, then pressed the latch rod in place, then cross drilled through the piston shell, end plug, and edge of the latch rod for the pressed retaining dowel, then machined the piston shell threaded end to trim the retaining dowel.

You can see where the piston shell crimp separated in the root of the crimp. Fortunately I'll be able to reuse the latch rod when fabricating a new piston, however the rest of the piston is "toast"!
  • Rougemont, NC

airnutz

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Re: Need info on odd (to me) HW55 piston I received for a rebuild.
« Reply #3 on: July 07, 2012, 02:56:40 PM »
nced,

I can't imagine the work involved if this piece was OEM.  This would not be lucrative in my opinion.  On the other hand, why should someone do the intense machining if the piston can be bought for less.  I didn't notice the piston cap was an alloy from the one I did recently.

Strange indeed, the seemingly hardest stressed part of the piston, the front, should be of a lesser hardened alloy.

It seems you do thorough work, my compliments.

Offline nced

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Re: Need info on odd (to me) HW55 piston I received for a rebuild.
« Reply #4 on: July 07, 2012, 07:35:26 PM »
"This would not be lucrative in my opinion".
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Yep, not very considering the time required, however it does pay almost equal with Micky "D"s, plus it's enjoyable.

A couple years ago a fellow had a HW55 piston that had been modified to use a "donut style" seal and he wanted to revert back to a factory seal. He sought "high and low" for a replacement piston everywhere from Beeman to HW in Germany and the piston simply wasn't available at any price. Well.....I reconstructed his piston and it was a different design than the one in the original post. Matter of fact, I've oring sealed a couple HW55s and their pistons were of a different type. Here's a couple pics of the piston after reconstruction.......


As you can see it's design is like a small R9 piston.

Since taking on this latest project I've learned that I must be working on a piston from an older HW55 and the "double slotted" was common.

I have built/modified quite a few pistons up to now and here are a few pics..........




Lower FWB124 piston was a special light weight version built completely from scratch, including the latch rod....these weren't cheap!  :o



Lightened and buttoned factory R1 piston with added oring sealed piston cap.




Home fabricated R9 piston with experimental molly filled nylon oring sealed piston cap. I've since nixed the molly filled nylon piston cap and reverted back to aluminum alloy.

Anywhoo.......I've made a few chips and SCRAP in my years of airgun mods!



« Last Edit: July 11, 2012, 10:37:51 AM by nced »
  • Rougemont, NC

Offline nced

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Re: Need info on odd (to me) HW55 piston I received for a rebuild.
« Reply #5 on: July 11, 2012, 10:35:13 AM »
Confirmed......early leather sealed HW55 pistons were "double slotted", whereas the later synthetic sealed pistons I worked were "single slotted".
  • Rougemont, NC

Offline robert w

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Re: Need info on odd (to me) HW55 piston I received for a rebuild.
« Reply #6 on: July 12, 2012, 08:17:27 PM »
i had my early hw-55 apart and it has 2 slots also but the piston looks totally diffrent from that 1 . is there a chance it is hitting at the front when shot ? ilke almost too long after all that extra works? realy diffrent . have you been on the yellow on vintage forum ? id ask there who knows
in 1939 hitler said give up your guns and germany will be a safer place... then a short time after all guns were taken ,he told the jews "board the train" a word in histroy

How do you word it... "Air Guns" or "AirGuns"?