Compression Problem ?

[Plester123]

Hello people, just finished after 4 hours of first time changing a spring. All back together and running ok. But when i came to chrono it a minute ago it chrono'd at 290 consistent. It was fitted with a systema 1J so it should be around the 328 mark. I have ptfe'd the hop but that has made no difference. Any other ideas before i buy a new cylinder and piston ?
thanks a lot

[Fuzzy]

Re: Compression Problem ?

This is pretty much the advice I got, and it worked for me so here goes.

When you rebuilt it did you remove lube or re lube the cylinder?

For compression take the gear box apart and then put then outside the gearbox assemble the cylinder head, piston head, piston and cylinder together. put a finger over the cylinder head nozzle and try and push the piston down, it should fight you quite a lot. Ideally you won't be able to move it all the way down without your finger being pushed off cylinder head.

If everything here is fine then put the nozzle from the tappet plate on the cylinder head and run the test again, you can get a lot of air escaping in there.

Finally, if you have a cylinder with ports in it make sure the ports are at the back :p

[Plester123]

Re: Compression Problem ?

hi, while i had it open i tried the pushing the piston into the cylinder test and had next to no compression just slipped what can be done about that ? will i need a new piston, cylinder and air nozzle ?

[Lee 303]

Re: Compression Problem ?

All you need is a new O-ring for the piston head

You could also soak the existing O-ring in car brake fluid
The brake fluid causes the rubber in the O-ring to swell and will often swell enough to form a good seal between O-ring and cylinder

[Fuzzy]

Re: Compression Problem ?

I've always thought of the brake fluid as a temporary solution. Most airsoft retailers sell them, they don't cost much at all. Just slap that in and apply a new coat of lube.

As for the lube you want to use silicon grease or Lith-Moly grease. I personally use stuff called "SuperLube O-Ring Grease" but was told by the good people at a major retailers specialising in car maintenance/bikes that "Comma CV & Lith-Moly Grease" is suitable for O-Rings and plastics.

The key really is you want it to be thick enough not to drip (silicon spray oil is too thin) and to not contain petroleum distillates/mineral oil that can eat plastics.


Edit: Did it slip both with the nozzle and with your finger directly on the cylinder head? Before you go buying a new O-Ring try it without the air nozzle, you can loose a lot of air in that gap and may just want a new nozzle with an o-ring included within it.

[JOE90]

Re: Compression Problem ?

dont test compression with the air nozzle or tappet plate attached, just purely test it with the cylinder and cylinder head, block all holes, push piston into cylinder, it shouldnt hit the bottom, if it does with ease, then grab an oring, also check the oring on the cylinder head, make sure its all lubed nicely when reassembing.

[Plester123]

Re: Compression Problem ?

thanks guys, had the gearbox open again and the compression is fine when the whole for the blowback is covered (G&G GR-16) so i believe its that where the bad seal is. Does anyone know how to disable the blowback so i can get a better seal ?
any help is greatly appreciated