Gp Version 2 Gearbox

[lazareth1]

Hey guys, 

 

I'm having trouble with a friend's g&p sentry m4 version 2 gearbox. 

 

I cant seem to get the fps up past 260 on 0.2g bbs. I think I've figured out though as the piston is being clamped in as the last owner has put a nuprol piston in it. 

 

Does anyone with experience of this brand know what other parts of the gearbox are not your standard v2? So far I see that the piston is probably smaller, the tappet plate is also different. 

 

Where can I get a factory piston for this gearbox? 

[Asomodai]

G&P cylinder heads are naff and a little smaller in diameter then usual. But to put an aftermarket one is the alignment holes need to widened. I tried it myself and ended up destroying the front end of the gearbox. I just bought a new gearbox case instead. 

 

[lazareth1]

46 minutes ago, Asomodai said:

G&P cylinder heads are naff and a little smaller in diameter then usual. But to put an aftermarket one is the alignment holes need to widened. I tried it myself and ended up destroying the front end of the gearbox. I just bought a new gearbox case instead. 

 

Hmm I replaced that with a standard cylinder head and it fit fine? 

 

Did you use the same piston in the new gearbox shell? 

[Asomodai]

48 minutes ago, lazareth1 said:

Hmm I replaced that with a standard cylinder head and it fit fine? 

 

Did you use the same piston in the new gearbox shell? 

Maybe it was just my gearbox shell. But it was definitely funky trying to fit a standard Cylinder head in. 

[johnnyj]

Been using,building and breaking  g&p guns for a very long time  and while the the have had issues over the years , spur axles bearings etc most fps issues I come across are spring , hop related .

 

If the new piston is binding on the shell its fast to check,  close the empty shell ( screwd shut) with just the piston in and push it back and forth should be nice and smooth along the guides. If its stiff at points make sure the shell have not been twisted.. seem that happen before .