Help fixing a gearbox (or repairing, advice needed)

[Enbernz]

Hey all,

Getting back into airsofting after a few years and I pulled out my old DBoys full metal HK416 and it's completely buggered.

I've ripped the whole thing apart and something is playing up with the gearbox and/or hopup and basically my BB's are dribbling out. They shoot about 30 feet before dropping and go about 40 feet overall at a push.

I'm looking to either buy a complete gearbox or rebuild this one. My issue with rebuilding is

1. I've never done it before (although I'm mechanically minded and I've watched about 20 hours of YouTube videos. I'm convinced I can do it successfully.)
2. I've got no idea what is and isn't working in the gearbox so I'm inclined to replace everything.

Problem I'm having is it appears to cost almost as much as a new gun to buy the bits to rebuild, and a similar amount for a complete gearbox.

I've found this JG V2 complete gearbox at ***** for about £70 with an M100 spring.

Is there anything inherently wrong with this gearbox, or should I be better just buying all the bits (at a cost of roughly £130 I've worked it out) and building it myself?

I'm looking to get the best value for money in fixing this gun. Option 3 would be scrap it and buy a new gun, however the body of this gun is VERY nice and it's entirely metal so seems a shame to waste it.

Thanks in advance for any and all help offered.

Ben

[sj_asc]

Re: Help fixing a gearbox (or repairing, advice needed)

I would avoid wasting that kind of money on a whole new gearbox which isn't significantly better than the one its replacing, and Dboy's spec external spec tends to be a little different to that of JG, so keeping the existing shell will likely save you a headache of compatibility problems with the externals (unless you are prepared to do a bit of work with the dremel).

Your most cost effective bet would be to work with the existing config and try to identify what caused the sealing problem in the first place.
For the issue of bbs dribbling out of the end, I would start with the hop assembly before digging into the gearbox (unless there is anything clearly wrong with the nozzle or tappet (cracked nozzle or nozzle not returning after being pressed in).

Check the hop bucking, and that the chamber is sprung correctly against the front of the gearbox.

Once you have identified the major sealing problem then you can work forwards with the rest of the parts.

[Enbernz]

Re: Help fixing a gearbox (or repairing, advice needed)

Awesome thanks for the speedy response!

So the gearbox that is currently in my gun came out of another gun years ago (it was an M4, mine is an HK416 which is an M4 variant I believe - could be wrong) and I honestly can't remember if it worked fully when it was swapped over.

The air nozzle has fraying around the end of it (it's plastic) and I did notice this when putting the gun back together however it didn't seem that it could be bad enough to reduce the speed of the BB that drastically - again I could be wrong.

Likewise I couldn't tell whether the hopup unit itself is damaged or broken - seeing as it's relatively cheap to replace perhaps I should start here?

[sj_asc]

Re: Help fixing a gearbox (or repairing, advice needed)

Ah okay. Is the box that's currently in there also d-boys?
As for the existing hop unit, check that it has all of the components first (including the spring that holds it to the front of the gearbox as this can be responsible for sealing issues too).

Also check the hop bucking as it is sealing part, if there are any rips/tears/folding then this could also cause severe fps problems.

[Sitting Duck]

Re: Help fixing a gearbox (or repairing, advice needed)

D-Boys m4 gearboxes are a bit qwirky but not bad

2 things spring to mind....

They are reinforced at spur gear and need machining out a bit to get any higher speed gears like 13:1 in there

The front of the gearbox is a bit thinner than others, the front of the cylinder head is about 2.65mm compared to others which is 3.1mm or so. This can cause misfeeds as nozzle or other hop units can protrude a bit more/less

So a little more care in checking stuff is needed on them but a nice box all the same
A Element G36 type is in mine but needed to add a o-ring to hop unit to push it away a whisker and feed perfectly on auto @ speed.

Quite a solid gun, mag wobble on 416 with tape but looks and feels nice - sling is a wise addition though

[Enbernz]

Re: Help fixing a gearbox (or repairing, advice needed)

Ah okay. Is the box that's currently in there also d-boys?
As for the existing hop unit, check that it has all of the components first (including the spring that holds it to the front of the gearbox as this can be responsible for sealing issues too).

Also check the hop bucking as it is sealing part, if there are any rips/tears/folding then this could also cause severe fps problems.

The gearbox currently in there is not a DBoys.

I actually think there may have been a very minor tear in the bucking, however it is over a solid part of the barrel so I would have thought it made no difference.

I may replace the hopup and see if it was that!