Replacement Pistons For Weihrauch HW55

[T 20]

Sounding all good there, Maestro. a Thank you for the chat and I'll look forward to hearing how this one goes.

No problem, Tone.

Today's plan of attack is to finish machining the dovetail arbor for the TX seal, crop the 19mm OD spring I've found which nicely fits the b2 piston and machine a 7mm bolt to fit the rear stock bolt --- I also have some sundry items to sort but by the end of the day I hope to be on the chrono.

[TonyL]

Us mere plebs spectate and learn in wonderment at your prowess.

[T 20]

Us mere plebs spectate and learn in wonderment at your prowess.

What are you after, Lembo ?

[T 20]

For anyone needing piston dimensions for a 50/55, these are the dimensions from my 69mm long stroked HW50 :-

image.jpg


Just add 4mm to the piston seal length to get the dimensions of a standard 65mm stroke piston.

[T 20]

No problem, Tone.

Today's plan of attack is to finish machining the dovetail arbor for the TX seal, crop the 19mm OD spring I've found which nicely fits the b2 piston and machine a 7mm bolt to fit the rear stock bolt --- I also have some sundry items to sort but by the end of the day I hope to be on the chrono.

Finished piston :-

image.jpg

image.jpg

image.jpg


I chopped the well used 19 mm X 3mm Meteor Spring I found to 25 coils/24 air gaps at 190mm long and put the gun together :-

image.jpg


Over the chrono she's running at 7.4ftlbs with .22" Hobby, which gives a good indication that running with with a .177" barrel as on the HW55 this b2 piston should easily make 6 ftlbs.



All the best Mick

[Shed tuner]

I bet you were tempted to weld up the top seam of that b2 piston "just because"...

Don't think I've ever seen a piston made from rolled steel sheet that is quite so thick.. must have taken quite a beast of a machine... or a lot of heat.

[T 20]

I bet you were tempted to weld up the top seam of that b2 piston "just because"...

Don't think I've ever seen a piston made from rolled steel sheet that is quite so thick.. must have taken quite a beast of a machine... or a lot of heat.

I was tempted, Jon, but I'll probably be scrapping the piston as I only bought to get the latchrod for another longstroke HW50 piston build.
In fact I only left off the longstroke HW50 build to check that the b2 piston could be a viable alternative in the HW55 for folks who needed one.

Surprisingly the b2 piston only weighs in at 200gm as standard, rather than machine the 1" piston to get it into a 25mm tube I only had to linish it down.

[TonyL]

What are you after, Lembo ?

Hee, hee, hee! Nothing, Mick, just happy that you more expert tuners are happy to share your experience with us all.

[TonyL]

Finished piston :-

image.jpg

image.jpg

image.jpg


I chopped the well used 19 mm X 3mm Meteor Spring I found to 25 coils/24 air gaps at 190mm long and put the gun together :-

image.jpg


Over the chrono she's running at 7.4ftlbs with .22" Hobby, which gives a good indication that running with with a .177" barrel as on the HW55 this b2 piston should easily make 6 ftlbs.



All the best Mick

Nice one, Uncle Mick.

[Mach 1.5]

Are you going to try and push the power to 10ft lbs Mick? Mach 1.5

[T 20]

Are you going to try and push the power to 10ft lbs Mick? Mach 1.5

Funny enough, Paul.

I put the gun together and the piston seal was quite tight, but as this was all being done to prove my theory that the b2 piston would work in a HW55 I wasn't that bothered, same with me using a knackered Spring.
I did however realise last night that I hadn't done a final machine to size on the piston seal arbor, so this morning I've stripped the piston out and machined the arbor, and reassembled the gun.

Over the chrono she's now doing 500fps with Superdomes and 550fps with Hobbies for a touch over 8ftlbs.

I doubt I'll be doing anything else with this setup as it's easier to long stroke to 72mm if I want any more power.

Not bad for the pile of parts you sold me, even at 8ftlbs.

[Mach 1.5]

Impressed I must say. Mach 1.5

[joffy]

Nice to see you posting informative stuff again not that you didn't anyways .....you know what I meant

[Mach 1.5]

So would the heavier 50 piston need a thicker gauge spring to power a 55!. Mach 1.5

[T 20]

So would the heavier 50 piston need a thicker gauge spring to power a 55!. Mach 1.5

I think the HW50 piston is about 200gm at standard 65mm stroke, same as the b2 piston's weight, Paul.

I'd be inclined to go with the standard sized Weihrauch 20mm OD HW50 spring with 3mm wire as this leaves a 2mm thick wall on the spring guide.
I think my custom 50/99 uses a 19mm OD spring with 3mm wire.