Hw35 optimal set up

[Shed tuner]

It's the only logical way of doing it though, Jon.

But saying that it's much cheaper and quicker to just buy and fit a later synthetic sealed piston at about £40.

even cheaper from the EU... and yes i agree, it was more "because i could"

[evert]

.......
Now due to the crosspin through the piston head I couldn't machine the piston back to give a full 71mm stroke and stopped at just over 70mm.

If I do want to go to a longer stroke I can simply remove the HW synthetic seal and alloy arbour and machine up an O ringed piston head which could easily take me to 72mm.

The piston as seen still needs 1mm or so removing from the rear of cocking lever slot before fitting to prevent the piston smashing into the cocking arm on firing --- I normally aim for a 1mm to 1.5mm clearance.

Hope this all makes sense ?

All the best Mick

I get nervous when you remove all that material, have you ever had a piston come apart during cocking after this modification?

[T 20]

I get nervous when you remove all that material, have you ever had a piston come apart during cocking after this modification?

So far so good, evert.

In reality though the insert in the piston is brazed to the outer body so cocking doesn't present a problem.

The crosspin is just holding the sear rod, so when the threaded alloy arbour is screwed to the sear rod and the gun is cocked the spring pressure is held by the crosspin and the arbour.

The piston could be further strengthened by plug welding the outer body to the insert but I've never felt the need to do so.



All the best Mick

[TonyL]

OK then Steve, so as not to disappoint.

First off I fit the leather sealed piston in the gun and take a few measurements to work from :-

Attachment 295504



Then I remove the leather seal :-

Attachment 295505



Then I machine the front face of the piston back by the calculated amount to get a 71mm stroke :-

Attachment 295506



The newly exposed piston rod is then threaded :-

Attachment 295507



A lump of alloy that's premachined for the seal groove is then screwed and glued onto the exposed rod :-

Attachment 295508



The seal arbour is then finish machined :-

Attachment 295509



Adding a seal you end up with this :-

Attachment 295510



Now due to the crosspin through the piston head I couldn't machine the piston back to give a full 71mm stroke and stopped at just over 70mm.

If I do want to go to a longer stroke I can simply remove the HW synthetic seal and alloy arbour and machine up an O ringed piston head which could easily take me to 72mm.

The piston as seen still needs 1mm or so removing from the rear of cocking lever slot before fitting to prevent the piston smashing into the cocking arm on firing --- I normally aim for a 1mm to 1.5mm clearance.


Hope this all makes sense ?




All the best Mick

Brilliant stuff, Mick.

[Weasle]

OK then Steve, so as not to disappoint.

First off I fit the leather sealed piston in the gun and take a few measurements to work from :-

Attachment 295504



Then I remove the leather seal :-

Attachment 295505



Then I machine the front face of the piston back by the calculated amount to get a 71mm stroke :-

Attachment 295506



The newly exposed piston rod is then threaded :-

Attachment 295507



A lump of alloy that's premachined for the seal groove is then screwed and glued onto the exposed rod :-

Attachment 295508



The seal arbour is then finish machined :-

Attachment 295509



Adding a seal you end up with this :-

Attachment 295510



Now due to the crosspin through the piston head I couldn't machine the piston back to give a full 71mm stroke and stopped at just over 70mm.

If I do want to go to a longer stroke I can simply remove the HW synthetic seal and alloy arbour and machine up an O ringed piston head which could easily take me to 72mm.

The piston as seen still needs 1mm or so removing from the rear of cocking lever slot before fitting to prevent the piston smashing into the cocking arm on firing --- I normally aim for a 1mm to 1.5mm clearance.


Hope this all makes sense ?




All the best Mick

Hi Mick

Many thanks for all the time and effort for this ...it all makes great sense.

Cheers Steve

[T 20]

Hi Mick

Many thanks for all the time and effort for this ...it all makes great sense.

Cheers Steve

No problem Steve

I'll probably only use this piston in my .177" HW35E until I get time to machine up another one of these :-

image.jpg


This is the rotating 71mm stroke piston I made for my last 35 build --- the only downside to this piston is the limitation of Spring choice, at present it's running at 12 with an oldschool HW50 Spring.




All the best Mick

[evert]

That is very nice!

[CapitalBee]

No problem Steve

I'll probably only use this piston in my .177" HW35E until I get time to machine up another one of these :-

image.jpg


This is the rotating 71mm stroke piston I made for my last 35 build --- the only downside to this piston is the limitation of Spring choice, at present it's running at 12 with an oldschool HW50 Spring.




All the best Mick

What kind of o/d does that limit your spring to Mick?

[TonyL]

No problem Steve

I'll probably only use this piston in my .177" HW35E until I get time to machine up another one of these :-

image.jpg


This is the rotating 71mm stroke piston I made for my last 35 build --- the only downside to this piston is the limitation of Spring choice, at present it's running at 12 with an oldschool HW50 Spring.




All the best Mick

And shoots BEAUTIFULLY!

I really didn't want to hand that one back to Mick when I had a try with it.

[T 20]

What kind of o/d does that limit your spring to Mick?

Hi Mark

I didn't keep a record of the ID but I'd guess it's about 19mm which limits me to 18.8mm OD spring.

So the only available springs I can easily get are a Meteor MK6 factory spring,Factory SMK spring or their Titan replacements.

[CapitalBee]

Hi Mark

I didn't keep a record of the ID but I'd guess it's about 19mm which limits me to 18.8mm OD spring.

So the only available springs I can easily get are a Meteor MK6 factory spring,Factory SMK spring or their Titan replacements.

I've used the Protek Meteor springs of that size for SMK refurb's. At a tenner each they're good value.

[Weasle]

No problem Steve

I'll probably only use this piston in my .177" HW35E until I get time to machine up another one of these :-

image.jpg


This is the rotating 71mm stroke piston I made for my last 35 build --- the only downside to this piston is the limitation of Spring choice, at present it's running at 12 with an oldschool HW50 Spring.




All the best Mick

Many thanks Mick...have you used a CD trigger to a modified topsear on the record.

Cheers Steve

[T 20]

Many thanks Mick...have you used a CD trigger or a modified topsear on the record.

Cheers Steve

Hi Steve

I modified the Rekord top sear for the simple reasons that TX CD units rarely come up for sale, and after fitting a CD to my rotating piston 77 I found it a real pain in the arse to do.



All the best Mick

[Weasle]

Hi Steve

I modified the Rekord top sear for the simple reasons that TX CD units rarely come up for sale, and after fitting a CD to my rotating piston 77 I found it a real pain in the arse to do.



All the best Mick

Many thanks Mick