Replacement Pistons For Weihrauch HW55

[T 20]

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

Life gets in the way at times, Jonathan.

First I went blind in my right eye --- hence no shooting, machining or posting.
Then my daughter bought a house needing lots of work from dad, both inside and out --- hence no time to post.
Then I went deaf.
Then I had a new lens fitted to my right eye.
Then I got diagnosed with cancer and started treatment in November.

Apart from that everything's good here.

[Mach 1.5]

Bloody hell Mick. Let's hope 2025 is a vast improvement for you. Mach 1.5

[T 20]

Many thanks for this. I ended up taking my 55 piston apart and dressing out the damage that had be caused by the 'Ox' spring to the ali head and bonding it back using green loctite, so far, touch wood its still holding up. I will, however follow your lead and get one.
BTW, I used a vortek adapter and seal that I had originally bought for a knackered G80, and again that seems to be working well.

Cheers Steve

Hi Steve

The b2 piston seems to work well enough and your Vortek adaptor and seal should fit if it has a 5mm retaining bolt.

The b2 piston could be spun by the latchrod in an electric drill to linish the bearing surfaces down to fit the 25mm Weihrauch tube.

I increased the depth of the cutout in the latchrod using a 4" angle grinder with a very small cutting disc in it, sounds bad but I use angle grinders on a daily basis so I didn't even worry about it --- a Dremel should do the same job, but slower.

The HW50 I've used as a guinea pig is running at 8ftlbs in .22" and has a really nice firing cycle, in fact it's that nice I may just keep it at 8ftlbs as a close range ratting gun.

[T 20]

Bloody hell Mick. Let's hope 2025 is a vast improvement for you. Mach 1.5

So far so good, Paul.

[T 20]

I wonder if that might make the '99 piston a viable option (for those with the lathe and prowess)?

With the 99 having a 26mm cylinder you'd have to remove 0.5mm off the piston walls which are normally 1.7mm thick in order to fit a HW55's 25mm cylinder, and I wouldn't think 1.2mm piston walls would be strong enough.

Also, from the pdf that David/Topdog sent me the lengthways dimensions of the 99 piston are completely different to the 50/55 piston dimensions which is why I looked elsewhere.

[TonyL]

Gotcha, Mick; cheers.

And top result with this little project so far.

[T 20]

Gotcha, Mick; cheers.

From memory, Tone.

Though the oldschool 50 action fits in the 99 stock the cylinders are completely different internally.

The 99 has a shorter transfer port and cylinder end plug than the old 50 meaning the cocking cutout in the 99 piston is extended closer to the piston tail.
The cocking geometry of the 99 is also different with the cocking lever pivot hole being about 4mm further forward in the barrel block compared to the old 50 --- this is what causes the galling issue.
This was all done in order to extend the 99's stroke to 71mm rather than the 65mm of the old 50 --- I'm pretty sure that the 99's stroke could easily be extended to 76mm if needed.

If you did try machining a 99 piston to fit an oldschool 50 you'd end up just using the piston rod as nothing else would fit.

[TonyL]

Thanks, Mick. Again, very concise, detailed information and really well explained.

[T 20]

By way of wrapping this thread up.

Today I disassembled the gun again and extended the cocking lever slot in the piston rearward by 3mm leaving a 4mm gap between the cocking lever and end of the slot when the piston is forward.

The standard b2 piston with TX seal had a 1mm gap which meant that I was still breaking the barrel latch while simultaneously starting to cock the piston.
With the extra 3mm gap, the barrel latch is released before the cocking arm engages with the piston tail so separating the two operations of breaking the barrel and cocking the piston.

I also polished the latchrod inside the piston as I noticed it was as rough as a badger's arse, doing this upped the velocity with Hobbies by 20fps to 570fps.
With that done I screwed the gun back together and fitted the rear trigger guard screw --- I leave the screw out until I consider the gun finished.


All the best Mick

[Weasle]

Hi Steve

The b2 piston seems to work well enough and your Vortek adaptor and seal should fit if it has a 5mm retaining bolt.

The b2 piston could be spun by the latchrod in an electric drill to linish the bearing surfaces down to fit the 25mm Weihrauch tube.

I increased the depth of the cutout in the latchrod using a 4" angle grinder with a very small cutting disc in it, sounds bad but I use angle grinders on a daily basis so I didn't even worry about it --- a Dremel should do the same job, but slower.

The HW50 I've used as a guinea pig is running at 8ftlbs in .22" and has a really nice firing cycle, in fact it's that nice I may just keep it at 8ftlbs as a close range ratting gun.

Hi Mick
Once again.....many thanks.
I shot the 55 at the range last Sunday and it had a lovely shot cycle, however it has a bit of a buzz from the spring. I'll be trying a new spring guide shortly as soon as I get my Myford back up and running.
I will however follow your example and build a replacement piston.
Once again....many thanks.
Steve