HW77 Tuning

[Scubashot]

Has the new piston seal had an opportunity to bed in?
After fitting a V Mach kit (including a new spring and seal) to my 1987 HW77 0.22" rifle the power was way down, even with all the preload washers installed.
As the seal bedded in the power just kept climbing. I had to remove all of the preload washers and collapse a coil of the spring to keep it legal. Even now I have to keep an eye on it and have had to reduce the thickness of the top hat to fine tune the power level.

[Phil Russell]

I wonder if the rifle is over sprung. Until you experience this for yourself it is difficult to imagine: a too strong a spring can actually result in a decrease in power. Certainly the amount of preload you have ... and I assume by preload you are referring to the length of spring sticking out of the cylinder before you try to put the trigger block back in, is quite a lot. My 77k runs at about 1cm and it is no effort to fit the back block.
Can you try removing all preload (power) washers and see where you get to? This may tell you a lot.
Cheers, Phil

[madcarlos]

Has the new piston seal had an opportunity to bed in?
After fitting a V Mach kit (including a new spring and seal) to my 1987 HW77 0.22" rifle the power was way down, even with all the preload washers installed.
As the seal bedded in the power just kept climbing. I had to remove all of the preload washers and collapse a coil of the spring to keep it legal. Even now I have to keep an eye on it and have had to reduce the thickness of the top hat to fine tune the power level.

I had the same as you with my 177 77k, Had to remove all the washers in the end but lucky enough its settled to about 11.2

[dtdukok]

Scuba, Phil, Carlos... many thanks for the input. It is appreciated.

I doubt the piston seal has had a chance to bed in yet and it was pretty snug on reassembly. The spring is HW from the TBT kit and I have read on here that the old 77s had quite a bit of preload as standard? And yes, I mean how much spring is on show before the trigger block goes back on.

Should I remove a coil or two then at the risk of having to get another spring if it makes things worse?

Adding or removing both the power washers made little difference either way.

Thanks again,

Darren

[deejayuu]

Not advice just relating my findings. HW 77 cal. .177 8.3 gn Superdome New seal tight 595 ft/sec
slacker seal but still push fit 740 ft/sec
slack seal piston falls under own weight 750 ft/sec
Got spring data somewhere, for the .22 and .177 will have a look if you're interested.
Both make power (too) easily. Very pleasant at around 11 ft.lb. with Superdomes.

[dtdukok]

I’m going to try losing a couple of coils but can the seal be taken down or is it just a waiting game to let it bed naturally?

Thanks,

Darren

[Scubashot]

I’m going to try losing a couple of coils but can the seal be taken down or is it just a waiting game to let it bed naturally?

Thanks,

Darren

It can be carefully resized until the piston will drop under its own weight until the TP is blocked. However, I always let mine wear in without interference. It may take a couple of tons of pellets to do so though.

[bozzer]

STOP

Don't start lopping off coils.

It's most likely a tight piston seal.

Take the rifle apart. Take out the comp tube and the piston. Degrease. Hold the rear end of the piston rod in your thumb and finger and see if you can slide it easily in and out. If it takes some pushing in or pulling out then it's too tight. It should slide in and out easily with just the tips of your thumb and finger. If you stand it up with the comp tube down and the piston rod at the top I wouldn't want it easily falling under it's own weight. I would want to be able to gently push the piston rod down with the tip of a finger and it falls easily.

Put a Marigold rubber glove on. Pull the piston back so that it draws air in through the transfer port. squeeze a finger or thumb over the TP hole and try and push the piston forwards. It should go a short distance and then you should hit resistance from the compressed air. When you let go of rod it should bounce back slightly.

If the seal is obviously too tight then I wouldn't waste time and pellets trying to shoot it to size. I chuck them up in a normal hand drill via the end of the piston rod. Then place some very fine Wet n Dry around the piston seal. Wrap it around so you are contacting all the circumference of the seal as best you can. Start the drill spinning ( maybe hold it flat on a table with the trigger locked on ). Use a curled finger and thumb to gently apply pressure around the seal with the Wet n Dry. Just a couple of seconds and retry in the comp tube ( let it cool for several seconds before trying ). Keep doing this until you achieve what I described above ( easy slide fit ).

When you are happy then re-lube and refit to rifle and retest power.

Also check the spring guides. Are they a tight fit inside the spring. Different opinions here ... some like them quite a firm fit so they will be a slide fit when the spring is compressed ( gun cocked ). I have them so they slide in and out quite easily. Certainly not a gravity fit but no real friction. If you have to push and pull hard to get them in and out then they are too tight in my opinion. This will also steal power.

Do these things first before you start chopping coils off.

Good luck and let us know how it goes.