Ancient TM M4A1 hop unit...fun n games...

[Egon_247]

So....

Having been given a 20+ year old TM  m4a1 by someone, Im trying to get it up and running again.

Gearbox done, gears, grease n shimming, new piston n m100 spring. All happily doing their thing.

Only issue now is that it had a 2 piece hop unit. But alas, one bit was missing along with the barrel. 😕

So I've attacked it with a Dremel and made one fit (an old g&g I had kicking about), bought a barrel too

There's no space in front of it for the spring. 

Upon test firing just now it doesn't feed at all well (1 in 3 shots) but when it does it's up to 0.8j. 

I get the feeling that the g&g hop unit is crap, it's not a rotary one, so I've ordered a zci one to go in it. 

 

Is the spring an absolute necessity?

I've heard tales of o rings being used to shim it back to the V2 gearbox. 

The mag lines up ok but my concern is that if I shim the hop back to the gearbox, the mag won't line up. 

 

Any thoughts? 

 

 

[Lozart]

The spring is there to make sure the nozzle seats against the hop rubber properly, that's all. You can definitely use O-rings but they're less forgiving of any magazine misalignment.

[Egon_247]

3 hours ago, Lozart said:

The spring is there to make sure the nozzle seats against the hop rubber properly, that's all. You can definitely use O-rings but they're less forgiving of any magazine misalignment.

Cheers matey. This is the first time I've done a hop unit that wasn't a straight swap. It's sat against the gearbox pretty solid but I'll give the o rings a shot 😁👍

[Egon_247]

Aha...eureka moment. Looked into the feed tube and the nozzle isn't clearing the tube enough to allow it to feed. 

Looks like it might be time for a sector delay thingy. Might pull it back far enough to work. 😁😂

[Rogerborg]

5 minutes ago, Egon_247 said:

Aha...eureka moment. Looked into the feed tube and the nozzle isn't clearing the tube enough to allow it to feed. 

Looks like it might be time for a sector delay thingy. Might pull it back far enough to work. 😁😂

 

Ah, that makes sense, especially if the tappet plate is a bit worn. Thanks for the followup, it's good to hear solutions to the questions.

[Egon_247]

1 hour ago, Rogerborg said:

 

Ah, that makes sense, especially if the tappet plate is a bit worn. Thanks for the followup, it's good to hear solutions to the questions.

I just tried a shorter nozzle and it's feeding, just at 0.2j. 😁😱😂

Looks like I need the original nozzle to come back a bit further to clear the feed tube. 

I wouldn't mind so much but the front wired M4 is a pig of a fiddle to do. 🤬😱😂

Actually, thinking about it, I can't do that cos the tappet plate is held against the cylinder head isn't it?

Oh well. Hop unit change. Grrr.