G&G CM16 gearbox

[RR01]

Hi,  not been on here for a long time, but have a problem.  I gave up airsoft about 7 years ago, but kept a fairly new G&G CM16 - 8L after I sold most of my other kit.  My grandson has started airsoft and I've loaned him the rifle until he's 18.  It started off fine, but over the last 6 monhths has lost speed and is now only doing about 210fps on 0.2s.  I've stripped and resealed the gearbox (I've seviced and built plenty in the past), greased everything and put in a new piston O ring and resealed the head.  Also fitted a new M100 spring from Zero One.  This didn't seem to make any difference and if you hold a finger over the end of the cylinder head outlet and push in the piston the air seems to leak. In the past I've built gearboxes so that they will compress and hold air without any leaks. 

So those that know, please what am I missing after so many years to get this back up to around 320-330?

 

[fafnirr]

Maybe the plastic parts cracked? Did you change the cylinder head and air nozzle o ring?

 

[RR01]

Didn't have a new cylinder head O ring, but used a trick I was shown years ago to wrap PTFE tape around the cylinder head where it fits in the cylinder and refit the O ring over that.  Makes a very tight seal.  That isn't leaking.  I've stripped it again today and removed and cleaned the piston head, stretched the O ring over the cylinder before refitting (something else I was shown years ago), regreased it with silicon grease and refitted.  Now seem to have a better air seal, but can't test as the battery is now flat and grandson didn't give me the charger.  Another short trip to Zero One seems inevitable to buy a spare charger.  Thanks for your feedback.

 

[Lozart]

wrap PTFE tape around the cylinder head 

View attachment 104245

 

[Speedbird_666]

Yeah - PTFE around the cylinder head is generally frowned upon these days, and stretching O-rings is often only a temporary fix as they tend to shrink back to their original size.

Whereabouts are you based? Sounds like you are close to Z1 - I am relatively local to Z1 (Christchurch) - I have some spare Cylinder and Piston Orings that you can have free.

Also - replace your hop rubber.

 

[RR01]

Hi Speedbird,

Yes, Poole Road, Bournemouth now, so quite close to ZO.  As I said I'm out of the loop, so rely on what was normal 7-10 years ago when I was still playing. I have plenty of new piston O rings curtesy of Airsoft World, but couldn't see and cylinder head O rings on their website, so one of those would be good.

I've replaced the hop unit and rubber with an SHS unit with the large adjuster wheel on the end and a twin prong hop rubber.  I used those in my rifles years ago to good effect and found them easier to set up.