HW35 mods?

[randl]

Hi , picked up an old leather sealed HW35 with single sided safety dating from approx 1980 I think ?!
I seem to remember that it’s possible to fit a complete piston with synthetic washer from a later version to help improve the firing cycle. So I’m thinking I will probably do this and also fit tbt spring and guide if he still does them ? ( I’ve been out of airguns for a bit!)
Will also look at possible leaky breach correction .
My main question is do people who have done this conversion feel the outcome has been beneficial?
And secondly is the transfer port left as standard ok with this piston change or does it need altering ? Ps it’s .177 with 19 inch barrel.
Thanks in advance. R

[Phil Russell]

Now I will most likely be shouted down on my views on an old model such as you have, but: why change it?
OK, leaky breach to be mended if it needs it ... really need to chrono and eliminate all other possibilities if the power is way down. No harm in replacing service parts as well if needed.
But then that is only my take on it ... and I can understand your desire to concentrate on the rifle as an instrument and to increase its efficiency rather than as a piece of airgun history as it is.
No idea about Tbt kits. Also no idea on real effects of updating the piston seal other than I believe just doing the seal with no other changes is not really recommended.
Cheers, Phil

[gtfreight]

I replaced the seal with a modern one last summer on my 1965 35 and sleeved the tp from 4mm down to 2.8 and it improved it. Saying that, I had it out last weekend for the first time in a while and it was a bit twangy so I'll be investigating that when I get a moment.

[tinbum]

I prefer the leather seal unmodified in older guns, other don't. I would try a couple first

[CapitalBee]

It might pay to get a measuring stick on the transfer port. I've had a few HW35's from this era and the TP can vary in size, even if a leather seal was fitted. I've had some with 2.8mm TP's and the larger 4mm ports; if it was 4mm, you might want to sleeve it down as Geoff has done, but 2.8mm is a straight swap from a leather sealed piston to the newer synthetic seal version. Don't go the route of the steel replacement adaptor on the old leather seal as it increases piston weight and further reduces the stroke of the piston (reducing the available power). A new piston with synthetic seal will give more stroke (approx 4mm) and lighter piston weight, giving a nicer shot cycle. If your TP is 4mm, I'd be tempted to renovate the leather seal on the original piston tbh as they can run very nicely.

[randl]

Ok thanks guys so far ?
I certainly don’t want to destroy a classic. I owned and an HW35 E back in the late seventies and loved it !
I haven’t shot it yet so can’t actually compare it the 80 and 95 I currently own .
I guess if it feels good after a relube I may leave as is . But I do remember people recommending piston and seal change for a better firing cycle. I certainly won’t be using the synthetic seal adapter for the standard piston.
My thinking was new piston adds a bit of stroke , so less spring needed and hopefully better manners .
I’ll measure the tp when I get a chance , I guess if it’s 4mm then it may stay as is !
Cheers R