Help stripping and sorting a HW35k

[T 20]

I have done mate, just haven't updated my profile on here.


Neil

Codder.

[Mr.Fixit-Norm]

Well I’ve made a start

The piston has been polished, the spring has had the sharp pointy end collapsed and cleaned up ( never new it was that easy to flatten a spring with nothing more than a blowtorch and a pair of 100yr old flat nose pliers - thanks tinbum video )
I took the pics before I’d done a bit of polishing on the spring ends, not gone mad as I suspect it won’t be the one I end up using.

I’ve also fashioned an insert for the oversize TP as well, I’ve put a 3mm hole down the middle and it’s a very tight fit at the moment ( have only pushed it in about 4mm so far ) I’ve left it attached to the doner brass for the time being till I measure up how long it needs to be, and do any tweaking also it’s not had the end cleaned up either.

I’ve also assembled the cylinder / piston / spring and trigger block with the trigger ( note to self, the safety pin and spring needs to be put in before the rear trigger pin is inserted ) ready for sorting after lunch

[T 20]

The transfer port is about 26mm long --- I normally taper the sleeve so that it just starts to get tight 1/2 to 3/4 of the way home.

http://www.airgunbbs.com/showthread....06#post6226406



All the best Mick

[Mr.Fixit-Norm]

The transfer port is about 26mm long --- I normally taper the sleeve so that it just starts to get tight 1/2 to 3/4 of the way home.

http://www.airgunbbs.com/showthread....06#post6226406



All the best Mick

Thanks Mick, handy to know. Looks like I’ll need to lengthen the sleeve a bit but that’s not an issue. There’s a definite lip on the inside close to the piston end of the port, not sure whether to leave that as a stop so the sleeve doesn’t go in too far or run a drill through to make it all the same size ?
I don’t think the lip is very big ( a 4.5mm drill goes right through ) and the hole is still bigger than 3mm so it may be better to leave it as is ?


Incidentally I weighed the piston before I reassembled it and it weighed 263g with the seal so that could be added to your chart

[Mr.Fixit-Norm]

The transfer port is about 26mm long --- I normally taper the sleeve so that it just starts to get tight 1/2 to 3/4 of the way home.

http://www.airgunbbs.com/showthread....06#post6226406



All the best Mick

This is odd, in your reply above it says 26mm, when the email came through with the notification of your reply it said 25mm - how strange

[Shed tuner]

Thanks Mick, handy to know. Looks like I’ll need to lengthen the sleeve a bit but that’s not an issue. There’s a definite lip on the inside close to the piston end of the port, not sure whether to leave that as a stop so the sleeve doesn’t go in too far or run a drill through to make it all the same size ?
I don’t think the lip is very big ( a 4.5mm drill goes right through ) and the hole is still bigger than 3mm so it may be better to leave it as is ?

problem with leaving the lip is for an unknown depth, there will now be a 4.5mm diameter void that will just waste air. However, if you could ascertain it's length, you could machine a step into your TP sleeve and knock it in from the front, abutting it to the lip, just like Mick prefers

[Mr.Fixit-Norm]

problem with leaving the lip is for an unknown depth, there will now be a 4.5mm diameter void that will just waste air. However, if you could ascertain it's length, you could machine a step into your TP sleeve and knock it in from the front, abutting it to the lip, just like Mick prefers

Hmmm yes, I’ll investigate that when I strip it down again in a little while.

I’ve just run a string through the combro ( god it’s an effort to cock ) and was surprised at the results. Given the cocking effort I was expecting it to maybe be a bit warm but no, it wasn’t !

I used std JSB’s as they’re my go to pellet and this is the results. Bit strange in the middle but might’ve been some odd weight pellets maybe ??
Ignoring the weird two in the middle it’s a 12ft/sec spread with a range of 9.6-10.1ftlbs , and still twanging like a mad twangy thing

Ft/sec.

530
532
527
527
522
494
502
527
527
530
524
534

[Mr.Fixit-Norm]

I suppose the question now is, if I sleeve the port down from 5.? To 3mm and eventually add the new spring/piston seal and guides will the power go up / go down or stay the same ???

Norm

[Shed tuner]

I suppose the question now is, if I sleeve the port down from 5.? To 3mm and eventually add the new spring/piston seal and guides will the power go up / go down or stay the same ???

Norm

the port sleeve will considerably increase the power and reduce the recoil ...

[Mr.Fixit-Norm]

the port sleeve will considerably increase the power and reduce the recoil ...

That sounds good, I’ve now measured the depth of the transfer port and its 24mm and machined up a sleeve with a 3mm port. I took a closer look at the existing port and it appears that rather than a step at the piston end, it’s actually a taper !

I’ve tried to machine the sleeve with a matching taper as well.

I also decided with my new found spring shortening skills to ‘go for it’ and cut two and a half coils of the existing spring, meaning there wasn’t any preload and I could screw the trigger block on without too much effort.
The result of which meant I can now cock it without risking a hernia, and butt pad shaped bruise on my upper thigh

Run through the chrono I was surprised to find it had made no difference at all to the power, a slight increase in the ft/sec spread but not much. The twang however now sounds very melodic and even has a tuning fork after ring too it

I did look around for something plastic to sleeve over the existing guide as it’s a very sloppy fit in the spring but I couldn’t find anything suitable, and the dog was giving me that ‘ stop making brass swarf and get my tea look ‘

Out of interest do you know what the expected ft/s spread would be with one of these guns ?

Norm

Ft/sec with coils removed

530
528
517
517
533
531
526
530
528
526
515
519
517

[Shed tuner]

any springer should be capable of a 20fps spread (+ or - 10 fps). With a modicum of tuning and settling 15 fps is easily acheived, and 10fps with consistent weight pelelts and a well bedded in gun is far from unnusual.

you will not notice 20fps spread at the target.

[TonyL]

Well done on your first attempt at shortening and refinishing a spring, Norm. You're a dab hand at it now and those skills will stand you in good stead for future tinkerings.

[Mr.Fixit-Norm]

Well done on your first attempt at shortening and refinishing a spring, Norm. You're a dab hand at it now and those skills will stand you in good stead for future tinkerings.

Haha, thanks Tony. It was surprisingly easy, I didn’t realise how little heat was required to bend the spring, especially a square section one.

[T 20]

This is odd, in your reply above it says 26mm, when the email came through with the notification of your reply it said 25mm - how strange

My bad, Norm.

From memory I'd made mine 25mm long, then I found the transfer port and SCR thread and noticed someone had written 26mm, so I simply edited my post when adding the link.
I'd rather you machined a transfer port 26mm long than make one 25mm long and find it too short.

After a bit more calculation last night, with a 5mm transfer port your 35 would have a Static Compression Ratio of 95-1.
Sleeving the port down to 3mm raises the SCR to 265-1.






All the best Mick

[Mr.Fixit-Norm]

My bad, Norm.

From memory I'd made mine 25mm long, then I found the transfer port and SCR thread and noticed someone had written 26mm, so I simply edited my post when adding the link.
I'd rather you machined a transfer port 26mm long than make one 25mm long and find it too short.

After a bit more calculation last night, with a 5mm transfer port your 35 would have a Static Compression Ratio of 95-1.
Sleeving the port down to 3mm raises the SCR to 265-1.


All the best Mick

Ahh that explains it, I guessed it was something like that

I’ve made the new one 27mm long just in case and it’s still attached to the doner brass until I take the gun apart again ( probably today ) so I can tweak the OD until I’m happy with the fit.

That’s a huge increase, I wonder what it’ll do for the power level and recoil ? If they both improve significantly it bodes well for the tinbum tuning kit

Cheers.