Is it wrong...

[vestlenning]

HW35's are something special on their own.
The transfer port size of the leather seal models was about 4,2 mm.
If nowadays you like to switch such an old system to a synthetic seal, easy-peasy with an adapter, the TP-size should consequently be reduced to about 3,0 mm.

Easily done by gluing in a brass tube like the ones available here:
http://wasana-airgun-tuning.de/shop/sonstiges/
Please scroll down little bit to:
Messingröhrchen 4 x 0,5 x 30mm für HW35 alt

Mine is a 1980 leather, now plastic piston seal. Nothing done to the TP but the rifle works just fine, consistent at about 220 m/s with JSB Exacts.

http://barx.org/airguns/?id=hw_35

[Geezer]

HW35's are something special on their own.
Mine was my very first AG and the one I started fettling with many years after the purchase.
Still love it.

One thing you should know:
Simultaneously to the introduction of the HW77 in 1980 the HW35 design was changed from leather to synthetic piston seal (from ser.no. 843636 on).

The transfer port size of the leather seal models was about 4,2 mm.
If nowadays you like to switch such an old system to a synthetic seal, easy-peasy with an adapter, the TP-size should consequently be reduced to about 3,0 mm.

Easily done by gluing in a brass tube like the ones available here:
http://wasana-airgun-tuning.de/shop/sonstiges/
Please scroll down little bit to:
Messingröhrchen 4 x 0,5 x 30mm für HW35 alt

I think that is correct on the 35 TPs and seals.

On a point of detail, the 77 came out in 1984. The 35 TP/seal change happened earlier and independently of changes to the 35.

[T 20]

If nowadays you like to switch such an old system to a synthetic seal, easy-peasy with an adapter,

Now I wouldn't bother with the adaptor on the leather sealed piston to convert to a synthetic seal for three good reasons.

1) John Knibbs is knocking out synthetic sealed Pistons complete with seal at £30.

2) The adaptor adds 27grams to an already heavy piston.

3) The adaptor reduces the already short stroke of the leather sealed piston by another 4mm.


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 to synthetic - 61mm stroke - piston weight 321g


Saying all that I do like to start off with the old leather sealed piston as you can machine the nose back easily to end up with a lightened piston with a 71mm stroke.




All the best Mick