Piston scuff marks

[Geezer]

Not sure Terry Robb would be my preferred source of tuning advice. And yes, I have (years ago) used some of his stuff, on a springer, without great results.

[Hsing-ee]

Just check that the port is clean and free of debris. I did this once on an HW35 and there was still a lip of metal on the inner side where the drill had not gone all the way through. I gentle ran a rat-tail file through the port and cleaned it off, instant 1 fpe increase in power.

I think they are best left alone, unless you have engineering facilities to put them back to how you found them, it is a critical part of the system and easily bolloxed up. Why does the Robb ream them? So he can sell reamers? Sticking a venturi in or countersinking them is going to change the volume of the port and could mess things up big time.

[rg627]

Hi.

I'm out of ideas. I have stripped the gun and polished the piston 3 times now. I have even tried to de burr the cocking slot and gently turned some wet and dry inside the cylinder in case there are burrs on the inside. I don't want to polish any more in case I take too much metal off.

Each time I reassemble, the gun cocks smooth for a few shots and then it gets scratchy again when cocking.

I've tried little grease, medium grease and relatively heavy on the piston tail.

Where am I going wrong?

Am I missing something obvious?

It's as if, like someone mentioned, the piston doesn't sit central \ parallel in the cylinder. Almost slightly diagonal if extremely exaggerated.

I just wanted the gun to be smooth to cock and shoot. I understand it will never be up there with the likes of air arms or 97k etc

Can anyone think of any other ideas?

[bighit]

what rifle is it ?

[rg627]

Hello

Hw99s .177

[bighit]

Hello

Hw99s .177

could it be the cocking link that's making it feel rough? the link could be galling on the cylinder . my HW99s in .22 was doing it after i fitted a tuning kit . i have stripped the rifle right down and will have to fix the galling issue after i refinish the stock.

mine is a 2003 model.

and i only noticed it was a HW99s when i reread your first post

[rg627]

Thanks, but I don't think it's that. It has one of these cocking links.

http://www.airgunspares.com/store/pr...Cocking-Lever/

I'll try one last go, failing that I'll have to get someone with more experience to have a look.

Anyone know of a good tuner in the Manchester area?

[RebornAirgunner]

Thanks, but I don't think it's that. It has one of these cocking links.

http://www.airgunspares.com/store/pr...Cocking-Lever/

I'll try one last go, failing that I'll have to get someone with more experience to have a look.

Anyone know of a good tuner in the Manchester area?

DM80, send him a pm

[Telephonepete]

Have you got the dreaded galling. Gun cocks ok at first then sounds rough on the cocking and return stroke. If so thats easy.

[Telephonepete]

[QUOTE=rg627;7386049]Thanks, but I don't think it's that. It has one of these cocking links.

http://www.airgunspares.com/store/pr...Cocking-Lever/

I'll try one last go, failing that I'll have to get someone with more experience to have a look.

Anyone know of a good tuner

[Telephonepete]

How old is your 99?

[rg627]

Yes it could be.

I've done some research and found a thread that suggested removing the spring under the plastic cocking link.

I will give that a go

[robs5230]

Message Shauny on here. He's a dab hand at sorting the 99. Sure he'll advise you

[Craig-P]

Yes it could be.

I've done some research and found a thread that suggested removing the spring under the plastic cocking link.

I will give that a go

That’s the one. Pull the delrin insert forward/out toward yourself and you’ll see the spring underneath. Just fish it out and job done.
Whilst you’ve got the arm out, dress and tidy the cocking arm ears.

[venoman]

V-Mach do a V-Glide kit to fit the 99s i have fitted a few and they work well.