HW 35 piston dimensions?

[MDriskill]

This is an odd request...but there is method to my madness, lol. If anyone has an HW 35 piston lying out, I'd be very interested to know how its length compares to this leather-sealed one from a 1980-vintage gun.

Thanks in advance...!

 

[flatrajectory]

I believe they are the same. What you shound be measuring is the metal piston body only, not including the seal.
Why do you need to know.?? if you don`t mind me asking.
Pete

 

[landymick]

The latch rod is shorter giving it a longer stroke .
The other piston is a 25mm 1968 HW 50 S for comparison.

 

[MDriskill]

Thank you gents! Very helpful info. (Please note my photo DOES include separate dimensions for head, body, and rod extension.) Basically, power on this gun is quite low, and I was wondering if it might be a 7.5 joule power-limited German action.

It's .177, has a 1980 serial, and is ostensibly a full-power US Beeman import, sans the dreaded "pentagon F" marking. But I can't get it to shoot much over 600 FPS. It's seen very little use, the piston seal and innards look near-new, and I've tried a full-power Jim Maccari mainspring.

I've read that some old HW 35's have problems with air leakage at the front receiver section's brazing. That looks fine to me too.

Another interesting detail is the transfer port is about 3mm in diameter. I have another leather-sealed 35, built before the limit went into effect in 1970, which has a 4mm port. I know 3mm is used on newer plastic-sealed HW's, but 4mm is typical for every other old leather-sealed HW 30/35/50/55 at my house.

 

[landymick]

I’ll try and check dimensions at some point .
It could well be the leaky plug syndrome. It’s worth sorting it out just to be sure , 4mm TP is common on older models yet my 1968 35S has a 3mm T.P
You could also try a new type piston and synthetic seal since you have the smaller port .

 

[landymick]

If the leather seal is too tight in the cylinder it will sap power but shoot nice

 

[flatrajectory]

MDriskill,
The tp for a 35 with a leather seal should be 4mm. Your 3mm tp is for the later synthetic piston seal. I have only recently tuned an older leather sealed 35 with the F in a pentagon stamped into the breech. As soon as I fitted new synthetic HW parachute seal, I gaind 100 fps in my .177 example. I also replaced the oem mainspring to a much lighter guage wire, as the oem HW mainspring is way too thick and very difficult to cock.
You will need a synthetic seal and a seal adapter, which screws on in place of the original leather seal assembly ,
see photo.
In the photo you will see the original leather seal, the steel adapter and below that a delrin seal adapter I made myself . The red seal is a ` Britseal` synthetic one, buyt the oem HW synthetis seal is equally as good.
Pete.

 

[flatrajectory]

Also.... the steel adapter weighs 40 grams !, so I turned down the very thick base part of the adapter ( in my photo it is upside down ), and parted it off so that is matched the dimensions of my delrin adapter. This reduced its weight to 18 grams, as the piton is already heavy at 300 grams. With this seal conversion and a softer mainspring my 35 . previously a 6 foot pound German market model, now gives me 10.5 to 11 fpe depending on pellet , in .177.
Pete.

 

[Rifle Captain]

I've got old one pre safety catch with leather seal. It's got a gauled transfer port from the barrel latch. Foes yours have this? .. I'll open the gun in due course to measure the piston but not right now as got my hands full.

 

[Deejayuu]

May not help.Can do more accurate if need be. For info., top piston was leather seal but adapted as @flatrajectory describes.
Overall length of later is shorter by 3mm but would be greater difference if leather seal stud was intact

 

[flatrajectory]

I've got old one pre safety catch with leather seal. It's got a gauled transfer port from the barrel latch. Foes yours have this? .. I'll open the gun in due course to measure the piston but not right now as got my hands full.

The tranfer port cannot be galled from the barrel latch, as the latch is way over to the l/h side. Explain please ?
Pete.

 

[Rifle Captain]

The tranfer port cannot be galled from the barrel latch, as the latch is way over to the l/h side. Explain please ?
Pete.

Yeah not the transfer port itself but that general area I.e within 10mm radius of the transfer port the barrel latch has gabled the rifle

 

[Rifle Captain]

Was a restoration project I have recently bought a welder and will bite the bullet and weld this groove and attempt to file it flat. It's otherwise destined for the scrap heap. 1960s 22 I believe

 

[flatrajectory]

Yeah not the transfer port itself but that general area I.e within 10mm radius of the transfer port the barrel latch has gabled the rifle

As long as the breech seal is sealing then do not worry, its comm and rarely has any effect unless absolutely dire.

 

[Rifle Captain]

It's not sealing. I might change it for a new one though and see if it works.

 

[MDriskill]

Was a restoration project I have recently bought a welder and will bite the bullet and weld this groove and attempt to file it flat. It's otherwise destined for the scrap heap. 1960s 22 I believe

Your photo shows residue from an old seal stuck to the standing breech face. Iif you cleaned that up and installed a new breech seal it would probably be fine. If the gun originally had a leather breech seal it may take some time to clean out its seat in the breech block, but a modern plastic HW breech seal is a drop in fit once that is done.

 

[MDriskill]

Gentlemen, thank you VERY much for these responses - your expertise and patience is much appreciated!

It appears that HW 35 pistons do indeed have some variation in length, and that mine is a longer one.

Re: transfer port - I have three old leather-sealed HW 35's. All are in excellent unmolested original condition, and all were ostensibly full-power US imports by Air Rifle Headquarters or Beeman. Together with a couple of interesting dates, they are:

+ 1966: HW 35E no. 241974 - 4mm TP
+ (1970: German 7.5J power restriction goes into effect.)
+ 1973: HW 35L no. 481499 - 3mm TP
+ 1980: HW 35EB no. 804176 - 3mm TP
+ (1980: No. 843636 is first Beeman HW 35 with plastic piston seal.)

So the TP size may involve something besides the piston seal material...though exactly what I can't say!

 

[Rifle Captain]

14.5 mm from front of piston assembly to the sear
TP is 4mm
Trigger laminated

 

[chouchin66]

Was a restoration project I have recently bought a welder and will bite the bullet and weld this groove and attempt to file it flat. It's otherwise destined for the scrap heap. 1960s 22 I believe

Don't go there with a welder ! You'll likely warp that fekker beyond belief...just keep mechanisim lubed & free.

 

[Rifle Captain]

Don't go there with a welder ! You'll likely warp that fekker beyond belief...just keep mechanisim lubed & free.

Will give breech seal a go. Failing that. A fast pass or a few tacks may be the last resort. Would be very chuffed to have this rifle working properly