just upgraded my leather HW35 to synthetic...

[T 20]

nah, when you unscrew the piston washer and holder, you get an m8 threaded rod sticking out. if you machine back the shoulder of the piston face, to increase the stroke, as i mention above, leaving the central section around 22 mm fo fit inside the tighter section of the seal, then screw on a machined ally disc 3mm thick to form the mushroom that retains the seal, around 6mm of that m8 rod will be left pocking through... just chop it off flush.

i did take a piccy, will post in up over the weekend.

defo sleeve down the port.. just loctite the tube in.

I do it a bit differently, Jon.

I measure the stroke and cocking lever gap and do a quick calculation before I start machining.

Then I machine the front of the piston back by the amount needed to end up with a 71mm stroke, naturally this leaves more of the latch rod exposed.

After threading the newly exposed latch rod I screw on an alloy or delrin arbour to take the synthetic seal.

A quick tickle with a Dremel on the rear of the cocking lever slot in the piston to give a 1mm clearance on the cocking lever and it's good to go.


Doing it this way removes more weight from the piston and gives more threads inside the arbour, but saying that, this still doesn't get the piston down to the weight of the factory synthetic sealed piston.





All the best Mick

[Shed tuner]

Doing it this way removes more weight from the piston and gives more threads inside the arbour, but saying that, this still doesn't get the piston down to the weight of the factory synthetic sealed piston.

All the best Mick

yeah, I get you.. I was slightly worried about only 3mm of threads in there, but then again, it's not really under any force. What is the weight of the factory synth piston ? I reckon I probably only saved 10g max over std leather.

[T 20]

What is the weight of the factory synth piston ? I reckon I probably only saved 10g max over std leather.

Here you go, Jon.



Here's the three strokes and weights of the three setups :-

Factory Synthetic sealed piston --------------------------------------- 69mm stroke - piston weight 264g

Factory Leather sealed piston ----------------------------------------- 65mm stroke - piston weight 294g

Leather sealed piston adapted via steel adaptor to synthetic ------- 61mm stroke - piston weight 321g

[deejayuu]

Here you go, Jon.



Here's the three strokes and weights of the three setups :-

Factory Synthetic sealed piston --------------------------------------- 69mm stroke - piston weight 264g

Factory Leather sealed piston ----------------------------------------- 65mm stroke - piston weight 294g

Leather sealed piston adapted via steel adaptor to synthetic ------- 61mm stroke - piston weight 321g

Thanks for sharing. Very handy. J

[Shed tuner]

cheers Mick, sounds like another reason to just buy a factor synth piston and be done with it.. 30g will be noticeable.

the steel conversion head looks like an absolutely horrible option...

[T 20]

This is the piston I made for my last 35, Jon :-

image.jpg

Even that could lose a little more weight, but it works.

[TonyL]

Here you go, Jon.



Here's the three strokes and weights of the three setups :-

Factory Synthetic sealed piston --------------------------------------- 69mm stroke - piston weight 264g

Factory Leather sealed piston ----------------------------------------- 65mm stroke - piston weight 294g

Leather sealed piston adapted via steel adaptor to synthetic ------- 61mm stroke - piston weight 321g

Brilliant information, Mick.

I remembered you had posted this before and that the weight saving was significant but couldn't remember exactly. Be great to have this info in the thread in Useful Information.

And I really must get one sorted for my old nail......that extra 8mm of stroke and 57g weight saving should make a huge difference.

[Shed tuner]

...that extra 8mm of stroke and 57g weight saving should make a huge difference.

you only get an extra 4-5mm tone, unless you are using the nasty head conversion as a baseline

[Geezer]

I have long been sceptical of these conversions. This thread has changed my mind. Thank you.

[Shed tuner]

I have long been sceptical of these conversions. This thread has changed my mind. Thank you.

You are most welcome to pop down to our club in New Malden one weekend morning and have a quick play mate... I was surprised at the improvement too.

(come via the A3, take the opportunity to get all those cylinders moving )

[TonyL]

you only get an extra 4-5mm tone, unless you are using the nasty head conversion as a baseline

I am, Jon.

When I first acquired the gun and stripped it, the original leather seal was well and truly goosed. I tried to get another leather one but everyone was telling me they weren't available. Then I rang Knibbs. Apparently in stock. Ordered by phone and it arrived......a leather to synthetic conversion.

Must admit, if I had far fewer guns I'd have done more work on it since its build (08/09), but it shoots very sweetly and I only use it for short range open sight garden duty. But I will be treating it to a later piston methinks.

[Shed tuner]

hah - then you will notice a huge improvement. Got a std leather head & seal here if you want it - let us know.

[evert]

I measure the stroke and cocking lever gap and do a quick calculation before I start machining.

Then I machine the front of the piston back by the amount needed to end up with a 71mm stroke, naturally this leaves more of the latch rod exposed.

After threading the newly exposed latch rod I screw on an alloy or delrin arbour to take the synthetic seal.

A quick tickle with a Dremel on the rear of the cocking lever slot in the piston to give a 1mm clearance on the cocking lever and it's good to go.

Why do you go for 71mm stroke? What stroke length can be achieved without adjusting the slot in the piston?
I'm a bit concerned about weakening both the piston skirt and the piston rod attachment.

[Shed tuner]

What stroke length can be achieved without adjusting the slot in the piston?
I'm a bit concerned about weakening both the piston skirt and the piston rod attachment.

you need to measure your own rifle mate, there's a bit of variation. mine was around 6mm. just see how much clearance you have from rear edge of cocking shoe, to the piston cocking slot rear edge. Whatever that is, you can increase the stroke by (allowing 2mm for clearance) without any further mods. Then measure the height of an hw 80 seal, compared with the leather nose, and then work out how much metal you need to remove from the piston for it to add up.

Piston still has plenty of engagement with the rod... if worried, just buy a new synth HW piston/seal.

[evert]

Thanks! Measuring is probably (like always) a good idea before I start cutting metal! Just curios to know what other people have found and done.
I've already converted to a synthetic seal, and the rifle is a transitional 1980 gun with a small transfer port.
Buying a new piston is not an option right now, since I've already overspent on airgun parts lately