Bit of post-fix advice required!

[dfrear]

I'd been having lots of trouble with my GR-16 gearbox recently, the story is as follows:

Went to a game and upon firing the gun bb's proceeded to roll out of the barrel with no power whatsoever, those that did manage flew around 1ft!

At first I thought this was to do with the hop as it's the last thing I'd messed with, field stripped and had a look - nothing wrong. Fired the gun without the front end to see just how much air was coming out of the gearbox, bugger all.

After getting her home I opened up the gearbox to find the piston completely stripped of all teeth and the 1 metal tooth knocked on its side. So having ordered a new piston (reinforced as I thought this was to do with the gearbox being reasonably high speed) I proceeded to fit the piston only to find that 90% of the time the gearbox locked up with the piston all the way back and the only way to fix that was to open it up.

So next I tried reshimming with new shims, cleaned and re-greased the gearbox while I was at it - same problem. Swiss cheesed the piston, took teeth off, adjusted AOE. Same problems.

At this point I noticed that the air nozzle was broken at the point at which is connects to the tappet plate! The nozzle had been loose the whole time. New nozzle ordered.

Gave up and ordered a TM piston on advice, piston arrived with a spring and all new piston head etc - installed "as is" and tested, popped new nozzle on. Perfect, no problems whatsoever.

However, the new TM spring was very weak (don't have a chrono so can't find out just how weak it was, but a few bb's were actually sticking to a cardboard box from 5ft rather than peircing it!) so I popped my old G&G standard spring in - which has always given around 350fps+

Now all the problems started again, locked up immediately. Opened her up and cut down the spring a little. Now with the spring cut down the gun fires as normal again - I haven't had a chance to test the performance but at least gearbox cycles again!

Now my question is, why would this occur? I haven't changed anything like the gears or the motor (G&P M120) and yet the box just doesn't like to work with that spring in it's original condition - even though it had for quite some time before that!

[jagillham]

Re: Bit of post-fix advice required!

What battery you running?

[dfrear]

Re: Bit of post-fix advice required!

Only an 8.4 but again, this hasn't changed either

[jagillham]

Re: Bit of post-fix advice required!

I'd suggest that maybe the battery did not have enough power for the job.

Low FPS with a TM spring isn't too much of a surprise, as they come in roughly 290fps. Cardboard can also be surprisingly tough!

[dfrear]

Re: Bit of post-fix advice required!

Aye, I wasn't expecting much of the TM spring - I only wanted the piston really, just so happens they all come as one for a very, very reasonable price lol.

This still doesn't really explain why that exact same battery has been completely fine in the past, with that same spring? Maybe the piston has been stripped for quite some time or something similar? It did seem to still draw the piston back ok, even with all the teeth removed lol

[jagillham]

Re: Bit of post-fix advice required!

Possibly the battery is coming to the end of it's life?

You've changed a lot of things, so many variables to consider, lol.

[dfrear]

Re: Bit of post-fix advice required!

Yea - I guess so, but the battery itself seems perfectly fine. I don't think I'll get to the bottom of this one, just have to chrono the gun next time I get to a game and see what happens.

Thanks for the suggestions

[Secretsquirrel]

Re: Bit of post-fix advice required!

Had something similar on a 416 and it turned out to be the motor going bad.
TM 1000 sorted it.

[jagillham]

Re: Bit of post-fix advice required!

I don't think I'll get to the bottom of this one

Welcome to the world of "airsoft tech" where you have to replace every part 5 times before it suddenly starts working again! :D

[laladijaan]

Re: Bit of post-fix advice required!

also had a simialr problem in the past too, turned out to be the bearing on the spring guide had failed (that is if you have a bearing on your spring guide )

[dfrear]

Re: Bit of post-fix advice required!

I believe I do have a bearing on there, may have a look at it. I'll probably drop a fresh gearbox in soon if I continue to have problems. That or sell a few guns and buy new again!

[Just an Airsofter]

Re: Bit of post-fix advice required!

wen you replaced the original piston, was it exactly the same dimensions internally as the original.

If it wasn't the locking up may well have been from the spring not having enough room to compress in the gap it had. The TM spring would have been weaker and would have compressed more. When you replaced it with the original, did you leave in the TM spacer block that holds in the TM spring and piston head? If you did the gap would have again been smaller and the spring wouldn't have been able to compress fully.

By clipping the spring you have removed coils which means the spring when compressed takes up less room.

Clipping the spring isn't an issue, as long as you put the cut portion into the piston, otherwise it will ride over the spring guide and cause further problems down the line.