Mp5k Version 3 Gearbox Spring Length

[Bar1975]

I am looking to upgrade my spring but the SHS M100 spring is a lot longer than the stock spring.

Are all springs compatible with all gearbox versions?

[Cliffradical]

What brand is your MP5K? How much longer is "A lot longer", 1/4"? 1/2"? 1"?

A spring should be a spring but if you're using a bearing spring guide and/ or a sorbo pad or silent piston head, you may have to check the angle of engagement and modify the piston to account for the travel distance.

Unless your gearbox is a way bizzarro V3, your spring should be fine. Sometimes you'll get a shorter but much stronger spring in a gun. A weaker spring can be longer while still creating less 'push' when releasing due to the difference in density between materials.
The point at which the sector gear interacts with the pickup tooth of the piston is the important part (AOE).

Edit: We still need more information, but when you re-assemble, make sure that the more tightly wound portion of the spring (if present) is sitting on the spring guide, not within the piston.
Second, if your spring really is too long, your piston can *potentially* bind and lock on that depending on the box and the dimensions of the piston mouth. The piston mouth can be modified to counteract that, but as I said; we need more information before that is even a concern.

[Styrak]

Different brand springs are different lengths, depending on many factors like material used, spring power, and just the brand itself.

There's no issue.

[Bar1975]

It's a Classic Army MP5K

I've rebuilt plenty of version 2's before and yes i do have a Sorbo pad and bearing spring guide on the way for this new one. I'll fix up the AOE no worries.. done it before.

With this particular gearbox it just seemed to me like the m100 spring i was putting in was way too long... i really had to cram it in there. I test fired a few shots and got some serious grinding noises... so much so that i think the GB locked up on me after only a few semi auto shots. (i stopped firing because i was afraid of destroying it)

I also replaced the bushings but did not alter the stock shimming job.. it's possible that I've got a shimming issue now as a result. I'll open it back up and check everything tonight

As long as there are no specific springs for different gearboxes then that removes the spring from the equation of why it locked up on me.

thanks for the help guys

[Cliffradical]

hmmmmm I've put an SHS 100 into a CA MP5K before... somethings not adding up.
Does the diameter of the mouth of the piston match the diameter of the spring with a bit of wiggle room, or do you have to cram that spring in there? Does the spring seat all the way into the piston?

As an aside, if you switched bushings you will definitely need to re-shim your gears. Stock CAs tend to sit quite high vs. other brands and you can be left with significant gaps where you had none before.

[Bar1975]

yea the stock bushings were plastic and very hard to punch out of the GB shell. I replaced them with 6mm Bearing bushings and noticed a significant amount of vertical play in the gears after putting it all back together.

So i guess that grinding/lock up sound that i heard after testing it was my gears getting stripped off those bearings!!!

The m100 spring fit the piston fine.. the only concern i had with the spring was that it seemed too long. But the gearbox went back together ok so it must be fine.

[THe_Silencer]

Spring length is NOT indicative of FPS.You should ALWAYS recheck your shimming after a gear a bushing change. Shimming is one of the most essential things to getting your mechbox to run smoothly. You should get that right first before worrying about AOE or sorbo pads. The reason you hear the grinding is because of your lack of proper shimming. If your gearbox still locks up after proper shimming, get a more powerful battering because the one you currently have isn't providing enough juice to pull the new spring.