HW 35 transfer port, your thoughts

[I. J.]

Good old Araldite would solve the problem, but with air chambers on here fetching about £20 posted why bother.

I have tried filling the dead space in the breach block with solder, which proved to be a tricky operation and very time consuming, and not very successfull.

After spending hours on the gun I decided to join the BBS, make new friends and wait until someone advertised the parts I needed.

All the best Mick

I remember the original article published in AGW by Gerald Cardew about the lost space when the end plug isn't solder correctly into the cylinder and this fault being responsible for low power in some examples.
What I wonder is why, with all the possible years of use, this, I take it to be a very small crack or flaw, has not filled up with the pressures involved with gunge, bits of leather washer and cr@p from normal useage?
Just a thought.

ATB
Ian

[99CLOMP]

I remember the original article published in AGW by Gerald Cardew about the lost space when the end plug isn't solder correctly into the cylinder and this fault being responsible for low power in some examples.
What I wonder is why, with all the possible years of use, this, I take it to be a very small crack or flaw, has not filled up with the pressures involved with gunge, bits of leather washer and cr@p from normal useage?
Just a thought.

ATB
Ian

A very good thought, but it makes no odd's, my .177 IS going to do 10ftlb, it is, it is, AAAAAAAAGH

[T 20]

Hi I.J
I think the reason the void in the chamber doesn't fill with crap is because the gap into it is very small, also the pressure entering the void on firing would blow back when the piston came to rest, so clearing itself.

The other good reason it hasn't filled, is the fact it was only producing 4.5 ftlb's when I got it and I haven't used it in 20 years. The only way I could humanely kill anything with it would be to smack whatever it is over the head with the butt. In all honesty my mate who gave me the gun never used it much either because he reckoned it was horrible to shoot. The gun recoils like made due to the piston slamming into the end of the chamber, this is caused by the lack of pressure build up in front of the piston.

Cheers Mick

[T 20]

I'm sorry to bump this thread back up, but as RustyBuzz said in his original post that one in three HW35's suffered with a faulty air chamber, that would be about 660,000, so I thought I'd pass on how I cured mine.
The original Airgun world article by Gerald Cardew raised two questions in my mind, what was the resin used to seal the chamber? and who the hell has a vacuum chamber in their house?

Last week I called in at John Knibb's place and bought a new Nylon piston seal and reasembled my 35, result - 420 fps.
I took the gun apart and machined down the piston washer OD to reduce friction a bit, result 380 fps. I also noticed that when the gun had been fired, the next time the gun was just cocked enough to slightly raise the piston I could hear trapped air escaping from the transfer port. The air was trapped in the void in the chamber and also in the anular groove in the piston washer. As I had reduced the OD of the Piston washer the anular groove had opened up to trap more air so lowering the velocity even further.

I stripped the gun again and machined up a brass plug just small enough to enter the air chamber this was used to lap the chamber out using grinding paste of decreasing grit sizes. when I was happy the cylinder was true I washed it out several times with celulose paint thinners. The brass plug was now put back into the lathe and I machined an O ring groove in it to accept a BSA mercury sized O ring. Now I had a clean chamber and a piston i could use to create a vacuum or produce pressure inside the chamber, all I needed to do now was to find something to fill the void with. I originally thought that Araldite would do the trick, but after mixing some up I realised it was far too thick so I had a look round my workshop and found a bottle of Locktite 271 Threadlocker. The Locktite is fairly thin so it would enter the void and when it dries it becomes really hard ( just the job ). I stood the air chamber upright and poured some Locktite into it so that it ran round the joint between the air chamber and the breach block, then I inserted the piston I had made. By pushing the piston to the bottom of the chamber and then blocking the transfer port with my finger, I was able to pull upwards on the piston to create a vacuum. I repeated this several times to make sure I had pulled all the air from the void in the chamber. The next step was to block the transfer port from the inside with a rubber bung and then use the dummy piston to pressurise the chamber. I used a drill press to push the piston down and I left the whole lot like that overnight to let the Locktite harden off.

The next day I released the piston from the chamber, removed the bung and removed the excess Locktite from the chamber. The next problem was the fact that I didn't have a piston seal to use. As the dummy piston I had made up was no longer needed I machined that down and tapped it so that it could be screwed onto the original piston threads which held the leather piston washer. After reasembling the gun using silicon oil on the piston head and a very thick molly grease on the ends of the spring I fired a few test shots to clear the action.

Over the crono the gun now produces
665 to 670 fps with Hobby's
610 to 613 fps with Superdomes
585 to 620 fps with Wasps
500 to 505 fps with Baracudas

I don't think the gun is really running right yet and it seems to be oversprung but I'll have to have a play with it again someday, but at least I've cured the chamber problem. I hope this lot is of some use to somebody else with a rogue HW 35.

All the best Mick

[baz]

The problem with the 35 was the length of the port rather than the size, and the porous brazing, some also had tapered cylinders which didnt help too much either

Its been a good while since I did much to one but I think the best overall size for the port was 3mm

[T 20]

I forgot to say the transfer port in the gun I've been playing with is 4mm diameter. I think this might be the result of someone trying to tune it due to it's terrible power output.
If the standard size of the port is 2.8mm then a 4mm port is double the volume, as I've posted earlier Mike Wade engineering recomended a 3.125mm port and Venom said they didn't alter the port when tuning.
I have a spare cylinder with a 2.8mm transfer port so I'll build that up when I get time and see what that one does.

All the best Mick

[99CLOMP]

I forgot to say the transfer port in the gun I've been playing with is 4mm diameter. I think this might be the result of someone trying to tune it due to it's terrible power output.
If the standard size of the port is 2.8mm then a 4mm port is double the volume, as I've posted earlier Mike Wade engineering recomended a 3.125mm port and Venom said they didn't alter the port when tuning.
I have a spare cylinder with a 2.8mm transfer port so I'll build that up when I get time and see what that one does.

All the best Mick

interesting stuff, I am waiting for a few bit and bobs from J Knibbs before I have a go at my 35e,

[T 20]

Hi 99CLOMP
As previously posted I managed to cure my cylinder problems but my 35 was twangy and felt very oversprung using the Titan XS mainspring. I know you have ordered the same spring from Knibbs' for your gun and your transfer port is about the same size as mine.

Today I decided to mess about with mainsprings to see if I could get my 35 to run better and not be so close to the limit. The Titan XS spring which I had originally fitted had about two inches of preload and I had to wind it into the chamber using the tailstock of the lathe as a spring compressor. The gun took a lot of effort to cock and was twangy and recoiled a fair bit on discharge. I took the XS spring out of the gun and had a look through my spare springs, the most obvious spring to try was the cut down OX which had come with the gun twenty years ago. The OX had been cut down to such an extent that when fitted it only stuck out of the spring chamber by half an inch and made the trigger housing dead easy to fit as there was next to no preload. I put the action back into the stock and fired a few shots off, the gun is now dead easy to cock and has hardly any recoil, in fact it's a pleasure to shoot and I was getting quite fond of it, after hating it for twenty years.


Then I made the mistake of checking it on the chrono.


Using the XS spring I was getting 665-670 fps with Hobby's


Using the cut down OX I'm now getting 720-730 fps with Hobby's


That averages out to about 14ftlb

I think the next step will have to be the machining of a new longer piston head to reduce the piston stroke. This should give a faster lock time even less recoil and hopefully less power as well.
All this messing about makes me wonder if all HW 35's had cylinder problems, but some were just worse than others.

All the best Mick

[99CLOMP]

thanks for the info mick, I have found one or two springs in my box, it will give me somthing to do on those dark winter nights,

[T 20]

Hi 99CLOMP
I think if I ever had to play with another 35 the first thing I'd do to it would be to degrease the chamber, then warm it up, stand it on end an run some Locktite round the breach joint.
If I was using a nylon piston head and it needed reducing in diameter I'd remove material from the front face of the head instead of the OD. As the piston seal is tapered, removing material from the front face would reduce the OD, lower the lost volume in the anular groove, and give a very slight increase in the piston stroke.

Hopefully on the dark winter nights I'll be lobbing .22 Hobbies at unsuspecting Rats.

All the best Mick

[99CLOMP]

It may be that the .177 is a home-market HW, where the rifles are restricted to 6 ft/lbs or so.

Check with another .177 owner before modding the port as once you have taken the metal out its difficult to put back! The transfer port is an incredibly sensitive link in the power train and it is easy to knacker a rifle by opening it out too much. Yours does sound rather narrow though.

One thought is that has it been drilled properly? My HW35E had a transfer port which was not completely drilled through and a lip of metal had been left, effectively closing off 20% of its area. I slipped a rat-tail mini-file though the port and opened it up as it was supposed to be and hey-presto! an extra 2 ft/lbs appeared!

well while waiting for some bits from J Knibbs (19 days and counting) I decided to get the 35e ready for a full tune, and noticed a tiny lip at the bottom of the transfer port, this may be why the gun was a bit low on power, any way the transfer port is now at 3.1mil In fairness to J knibbs I have ordered a new piston( but they did state a week or two) just got to hope the lady who took my order under stood "I dont want a screw on head"

[I. J.]

just got to hope the lady who took my order under stood "I dont want a screw on head"

With a mush like yours I thought you would have wanted to change heads.

Good luck with the re-built. It should be ready (and run in) for the Classic/Collectors meeting of 1st Feb. at our indoor range.

ATB
Ian

[99CLOMP]

With a mush like yours I thought you would have wanted to change heads.

Good luck with the re-built. It should be ready (and run in) for the Classic/Collectors meeting of 1st Feb. at our indoor range.

ATB
Ian

My Mrs says I have always got my DAFT head on

[dvd]

I like these hands on threads very much.
I wonder if the vacuum bags that are used to pack clothes and bulky clothing to make them into a smaller package, can be used to create the vacuum "chamber "required to have the glue sucked into all voids in the cylinder plug joint?
The setup just needs a vacuum cleaner and a cheap plastic packing bag as described.
Mrs can use it later as well!
Just a thought.

[TonyL]

Brilliantly timed thread revival.

It was great to read people's references to the Cardew article and to read of T20's early posts of 11 years ago on this very topical subject.

And Mick will also be the one most in the know on this........earlier, leather sealed guns have a larger diameter TP and later ones with the synthetic seal run a smaller one.