HW77 Tuning

[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.

[bozzer]

I can't seem to edit the above post.

I re read through your posts and saw that you fitted a Tin Bum kit. So the spring and guides will be fine. So concentrate on sizing the piston seal.

There was a post on here where someone resized them a different way. They degreased, then fitted new seal. Then put piston ( with new seal ) inside comp tube. They then dropped the comp tube and piston inside a pot of boiling water and boiled the lot for about 10 mins. Then remove from water and allow to cool. Dry completely with paper and hair dryer. Apparently the seal is sized. I've not done this myself.

Other advice is available.

[dtdukok]

I’ll try this before going for the chop - thanks Bozzer 👍

[Rickenbacker]

Don't know if it's already been suggested (haven't read the thread properly ), but 2.5" preload? Tight?

Have you checked that it's not something daft like a 26mm piston seal shoehorned into a 25mm comp' tube?

[dtdukok]

It was bought as a 25mm seal but mistakes do happen so I’ll measure it when it is stripped in the morning just to be sure.

Thanks,

Darren