Tuning HW35 Tuning

Jump to latest Follow Reply
FWB127 said:
Seeking recommendations for spring etc to get my 35s running closer to 12ft lb?

Will retain leather piston washers ( pre safety guns) Any preference for spring will be appreciated information!
Click to expand...
Why would you want leather piston seals when you can use a lighter spring to get equal or better power with a synthetic seal as it’s far more efficient

I’d be looking at a short .135 wire spring
 
  • Like
Reactions: Singleshot and FWB127
Upvote 0
Sometimes there's weird idosyncracies with the some pre saftey models. I dont want to steer you wrong guessing. Jim Macarri at Air Rifle Headquarters is the best person to contact about them. He makes excellent kits too.

I will say you'll need to keep it leather piston sealed. The leather guns use a larger transfer port to accommodate dieseling. You’ll loose considerable power converting it to a synthetic piston seal.
 
  • Like
Reactions: FWB127 and MDriskill
Upvote 0
FWB127 said:
Didn't want to touch transfer port
Click to expand...
For sure. I never mess with them. Keep the rifle leather sealed and you won't have to. I believe the there's no issues replacing a leather breech seal directly with a new style Weihrauch synthetic seal. Don't use aftermarket breech seals they're often too hard and or too thick and cause lock up and droop issues. Mike Driskill is an excellent source for information on these older rifles.

Be well
Ron
 
  • Like
Reactions: MDriskill and FWB127
Upvote 0
PaulK62 said:
I've never heard of anyone having to modify the transfer port when converting from leather to synthetic piston seals. Could you please explain, what does the transfer port have to do with what type of material the piston seal is made out of?
Click to expand...
I'm no expert thats why I've asked too! But there are plenty of threads on the internet Just google "HW35 leather seal transfer port" Apologies I couldn't help
 
  • Like
Reactions: PaulK62
Upvote 0
PaulK62 said:
I've never heard of anyone having to modify the transfer port when converting from leather to synthetic piston seals. Could you please explain, what does the transfer port have to do with what type of material the piston seal is made out of?
Click to expand...
The leather sealed Weihrauchs use a ~4mm transfer port. Synthetic sealed ~3mm.

Leather sealed guns use a larger transfer port to reduce peak pressure to accommodate and compensate for additional pressures from dieseling. Leather sealed guns require an oil soaked seal to seal properly and survive. That oil combusts controlably under pressure. That combustion is dieseling. The combustion adds pressure on top of the mechanical compression pressure.

Synthetic seals don't require oil or nearly as much lubrication. Because there's no deliberate significant dieseling from an oil soaked seal, peak pressures are reduced and velocity slowed when using the synthetic seals with larger leather seal sized transfer ports.
 
  • Like
Reactions: PaulK62, FWB127 and MDriskill
Upvote 0
Yup! A great explanation, and I can verify these numbers are correct on the old HW's lying around my house.

I've noticed that transfer port size is discussed more on the UK forums - no doubt an important variable when trying to optimize velocity and firing behavior within their 12 foot-pound power limit.

Weihrauch started transitioning to synthetic piston seals in the early 1980's, but I think it was actually a bit later before they figured out the optimum port size. Shouldn't be an issue on any recently manufactured one, but you might find an oddball oldster out there.
 
Last edited:
  • Like
Reactions: PaulK62
Upvote 0
MDriskill said:
Yup! I can verify these numbers are correct on the old HW's lying around my house.

I've noticed that transfer port size is discussed more on the UK forums - no doubt an important variable when trying to optimize velocity and firing behavior within their 12 foot-pound power limit.

Weihrauch started transitioning to synthetic piston seals in the early 1980's, but I think it was actually a bit later before they figured out the optimum port size. Shouldn't be an issue on any recently manufactured one, but you might find an oddball oldster our there.
Click to expand...
maybe just changing the leather seal to a new synthetic one would lower the FPE to the around 12 FPE he wants ? no trans port reduction ?
 
  • Like
Reactions: FWB127
Upvote 0
A.G.R said:
At a harsher shot cycle. 2.8 to 3mm is what you want.. the HW 35 has a much longer port than the Hw 80
piston is heavy.
Click to expand...
thanks , i would go for the smoothest shot cycle even at much reduced power (not a power guy ) I an a big fan of the 8 or 10 FPE UK FT shooters .
 
  • Like
Reactions: FWB127 and Motorhead
Upvote 0
I have a vintage 1969 HW35 with a 4mm transfer port and a leather seal. It's all original internally and deliberately sprung to be low powered.
The leather seal is in good shape and the seal it makes in the cylinder is also very good. The shot cycle is nice and smooth, but power is not quite as consistent as I'd like, although that could also be down to the pellets or the chrono.
I thought I would try reducing the transfer port diameter to see what difference it made to the shot cycle and power.
For that, I used a 4mm OD brass tube, with a 3mm ID bore, cut to the full length of the transfer port.
The last of my findings puzzles me:
  • Shot cycle still feels the same: nice and smooth
  • No dieseling resulting from the change
  • Power is the same!
What would be the expected outcome of reducing the transfer port diameter on such a set-up?
Cheers!:)
 
Upvote 0
Swissair said:
I have a vintage 1969 HW35 with a 4mm transfer port and a leather seal. It's all original internally and deliberately sprung to be low powered.
The leather seal is in good shape and the seal it makes in the cylinder is also very good. The shot cycle is nice and smooth, but power is not quite as consistent as I'd like, although that could also be down to the pellets or the chrono.
I thought I would try reducing the transfer port diameter to see what difference it made to the shot cycle and power.
For that, I used a 4mm OD brass tube, with a 3mm ID bore, cut to the full length of the transfer port.
The last of my findings puzzles me:
  • Shot cycle still feels the same: nice and smooth
  • No dieseling resulting from the change
  • Power is the same!
What would be the expected outcome of reducing the transfer port diameter on such a set-up?
Cheers!:)
Click to expand...
Change to a synthetic seal and you will see differences.
 
Upvote 0
Some of the early 35's suffered from poor brazing (cylinder plug to main tube) here.....

Screenshot_20241015_161522_Gallery.jpg



.....which creates a huge amount of lost volume, or in other words horribly low compression ratio (on a rifle that already has a very low comp ratio). Im not saying this IS causing your results, but if yours is suffering from this you'll struggle to make 7-8ish fpe no matter what tuning is done.

If it does have this issue it can be resolved by thoroughly degreasing the cylinder, bunging up the TP, squirting a thin loctite around the join, and then holding it under either compression or vacuum (with the piston) so the air in the void is replaced by the loctite. It doesn't need de brazing as per my pic, that's just an example from a 25mm conversion I did on a leaky 35 a while back. All the best.....
 
  • Like
Reactions: MDriskill and Swissair
Upvote 0
JamieUK said:
Some of the early 35's suffered from poor brazing (cylinder plug to main tube) here.....

View attachment 504533


.....which creates a huge amount of lost volume, or in other words horribly low compression ratio (on a rifle that already has a very low comp ratio). Im not saying this IS causing your results, but if yours is suffering from this you'll struggle to make 7-8ish fpe no matter what tuning is done.

If it does have this issue it can be resolved by thoroughly degreasing the cylinder, bunging up the TP, squirting a thin loctite around the join, and then holding it under either compression or vacuum (with the piston) so the air in the void is replaced by the loctite. It doesn't need de brazing as per my pic, that's just an example from a 25mm conversion I did on a leaky 35 a while back. All the best.....
Click to expand...
Thanks for this feedback. Appreciated. I will look into this.
 
  • Like
Reactions: JamieUK
Upvote 0
My HW35 was made just before the turn of the century.
HW35E
I went the 12fpe route with the VORTEK kit.
Didn’t like it.
I went the high power route with the R1 too.
Didn’t like it.
I have all my springers (The three TX200s, too) back to factory specs.
Including the HW35 which has a new factory spring, piston seal, beech seal.
They are fine the way they are..

IMG_0262.jpeg


IMG_2844.jpeg
 
  • Like
Reactions: fishing43
Upvote 0
You must log in or register to reply here.
Top Bottom
Back
Home
Forums
Resources
Menu