Weihrauch HW55

[nick_mantis]

Hello,

What is the likelyhood of being able to get a replacement piston for an HW55? Mine packed up last week, and removing the cocking lever the piston is sliding separately to the spring.

Sliding it back towards the trigger i can see the slot, and the piston stops just before the 2 sides of the slot meet. It would appear that it has cracked at the fore-end of the slot and the whole front of it has detached and will come out in 2 pieces

[Mach 1.5]

You may have trouble get a 55 Piston but the old HW50 piston will also fit. Failing this I dare say one of the engineers on here could repair or make you a new one? Mach 1.5

[nick_mantis]

Yeah, was kind of expecting that. Already been on the chambers website who carry quite a few spares and a piston they do not have.

The next question would be were all the pistons the same throughout the life of the 55 or were there some changes as with the others. The serial number on mine dates to 1980.

The slight issue is that I have been putting some money aside for a Feinwerkbau or Pardini to be able to retire the Weihrauch for occasional use. But not quite there to go out and buy one yet.

Winter competition season has already started and have about 3 to 4 weeks to get it fixed or possibly withdraw this time and get ready for next year. Also means it needs to be as accurate as it was before last week and not just back together and working.

It's 42 years old so knew at some point there would be an issue that would be difficult to fix easily due to parts, just hoped it would be in the future!

[Mach 1.5]

You could always try protek or place a wanted ad. Chambers will not stock the old HW stuff as it's no longer produce. Mach 1.5

[T 20]

Hello,

What is the likelyhood of being able to get a replacement piston for an HW55? Mine packed up last week, and removing the cocking lever the piston is sliding separately to the spring.

Sliding it back towards the trigger i can see the slot, and the piston stops just before the 2 sides of the slot meet. It would appear that it has cracked at the fore-end of the slot and the whole front of it has detached and will come out in 2 pieces

As your latch rod sounds to be OK, a piston repair by having a new piston body machined up would be the easiest long term fix option.
The piston bodies are just made from mild steel so anyone with a small lathe should be able to make one.
The only big decision to make is do you go with the original leather piston seal or do you machine the new body to accept a synthetic seal ?



All the best Mick

[rapidshot]

Sent you a PM

[evert]

Could you take some pictures of the piston?

[deejayuu]

Got two early 50 pistons on way from Netherlands. Not cheap but may be able to assist. I only really need one but saw this and bagged both.

[nick_mantis]

Misplaced my punch set but finally got everything apart this week.

Hmmm, maybe not quite standard. Anyone recognise it?

[T 20]

What is the likelyhood of being able to get a replacement piston for an HW55?

Having rummaged through my spare piston box this morning I have found a piston from a different manufacturer that would work in a HW55 --- the early SMK B2 piston.

The early leather sealed B2 piston and in its converted to synthetic seal form will fit the HW55 with the minimum amount of work --- the only downside is that it will give 8mm less stroke than the HW55 piston, but at 6ftlbs that shouldn't matter.

NOT this late B2 piston :-

image.jpg



The B2 synthetic converted piston would need machining down to sub 25mm on the flared front and rear sections as it's designed for a 25.4 cylinder, the cutout in the latchrod for the trigger sear would need deepening by 1mm and the seal would need changing for a TX200 one --- that's about all you'd need to do for an 8mm short stroke piston.

Now if you wanted more stroke, you could machine off the welded on SMK synthetic seal seal adaptor and move the seal back to gain 5.5mm of stroke --- obviously the cocking lever slot in the piston would need extending rear wards to suit.



The only modification needed to the gun for this to work is the drilling out of the latchrod hole in the back block to 10mm.





All the best Mick

[T 20]

Here's a HW50 and B2 piston side by side for comparison :-

image.jpg

image.jpg


From the first picture you can clearly see the 5.5mm section behind the seal on the B2 piston which could be removed.

Some dimensions:-

HW50 piston weight = 202g

B2 piston weight = 222g

HW50 stroke = 65mm

HW50 stroke with standard B2 piston = 57mm

HW50 stroke with B2 piston with 5.5mm seal arbor removed = 62.5mm


It could well be the case that the B2 latchrod is brazed into the piston nose and if so it should be possible to heat the piston's head to melt the braze and then simply knock the rod forward to increase the stroke.



All the best Mick

[Mach 1.5]

Just found this on the web with the mention of the alloy piston head.
The thing about the HW55 is that a lot of though went into balancing the powerplant to keep recoil to an absolute minimum. They don't give this kind of attention to any of their other guns.

They had 25mm pistons, but were much thinner, and had a big slot cut from the side opposite the cocking slot to make it as light as possible. The nose of the piston was also aluminum to save a bunch of weight. Less weight moving at the shot, means less recoil and quicker locktime.
But...
A piston that light would have a ton of bounce. So they made the transfer port 4mm to eliminate the bounce which would destroy accuracy. They kept the leather seal so that it wouldn't deform when it smacked the front of the compression tube, and it also offered less friction in the tube.

So with a 4mm TP would the internals from its sister the HW50 get the HW55 up to 10ft lbs.. ?

Mach 1.5

[HW777]

Just found this on the web with the mention of the alloy piston head.
The thing about the HW55 is that a lot of though went into balancing the powerplant to keep recoil to an absolute minimum. They don't give this kind of attention to any of their other guns.

They had 25mm pistons, but were much thinner, and had a big slot cut from the side opposite the cocking slot to make it as light as possible. The nose of the piston was also aluminum to save a bunch of weight. Less weight moving at the shot, means less recoil and quicker locktime.
But...
A piston that light would have a ton of bounce. So they made the transfer port 4mm to eliminate the bounce which would destroy accuracy. They kept the leather seal so that it wouldn't deform when it smacked the front of the compression tube, and it also offered less friction in the tube.

So with a 4mm TP would the internals from its sister the HW50 get the HW50 up to 10ft lbs.. ?

Mach 1.5

Chase the power in a 25mm Hw50 but let the 55's shot at the power they were intended for

[evert]

Chase the power in a 25mm Hw50 but let the 55's shot at the power they were intended for

Or do the opposite- use the heavyweight gun when you want to push power out of the system...