Gen 8 Box Tail Problems

We all know the manufacturing tolerances of Jinming boxes are unbelievably loose but I keep having the same problem with my gearbox tail after trying three different boxes. When I load the spring and push the gearbox tail in, I’ve noticed it doesn’t sit flush in the housing and wiggles heaps. Effectively when the piston gets pushed back the spring buckles. I’ve been looking at gearbox tails on eBay and other places but I have no idea how I can be sure it will be the right size. What do I do?


Well looks like you have other problems there. I’ve never seen a spring guide bend like that so I’d get a metal one. Also I’d get one with a bearing so the spring can turn as it compresses if it needs to
Next it looks like the back of your gearbox is broken so you need to do something about that. The spring retainer should not be loose like that.

And what thickness is that spring? I guess if the motor can compress it it can’t be too strong…

The other thing I’d look at to prevent future problems is when the gearbox is in place and your blaster is assembled ready to use, there needs to be some support behind the gearbox. That way it’s not just a few mm of plastic taking all the force.

It’s running a 1.3 spring at the moment but have run an uneven 1.4 spring with my usual nylon box. I’m just using the plastic box so you can see the problem.
I want to buy a spring guide but most of the ones I’ve found are for gen 9/10 boxes and the ones I have seen for gen 8 look like the same products rebranded by people who don’t know any better.
Do you know anywhere I can get a guide you know will fit?

OK, I tried to replicate that (I have a Gen9 though) by purposely bending a spring like that and wasn’t able to get the stock spring guide to move (even without the screws clamping the case down)

Note: I compressed the spring more than that but its hard to do so with one hand while holding the case together and taking a photo :stuck_out_tongue:

Maybe your case is damaged where the spring guide rests, after twisting, leaving it free to float around a bit?

Edit: Compressed further (holds pretty damn well)

Idk if this helps at all but these are the dimensions of a stock gen 9 spring guide (might be the same as the gen 8?)

Lol, excuse the tablets in the background (I dumped them [inner health plus?] to use the bottle for something else)

I received a so called “gen8 metal spring guide” last week from AliExpress… I’ll measure it up and post the results… Haven’t put it in anything yet so the gods only know what it fits…

Edit, here ya go…

So that’s looking a lot like @XTOPC results…
Perhaps my gen8 is gen9 or they are the same…

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I added more pics after seeing yours and it seems the cap is 1mm thicker?

Might be worth checking the position of the pins on the side of the cap too (their depth)

Actually, that metal one is gen9
Gen 8 is totally different

Just remembered I have a tarvor with a gen 8 gearbox…

Little bastard nearly took my eye out when I removed it :dizzy_face:


That looks like stress fractures when your spring guide inserts