G&Gm4 Lockup
 

Hey guys,

Unfortunately I can usually figure things out but this problem is weird.

Shims are working properly (Checked shism and work great)
Motor is working properly (used 2 different motors)
Used an 8.4v and 9.6v batteries, both charged.

Ball bearing spring guide
ball bearing piston head
silent piston head

Basically, I put the gearbox back together pull the trigger and it fires a good 3 round burst. But after the gearbox simply seizes up.

The piston simply gets stuck in the back near the spring guide. I know the spring is not buckling over the side of the spring guide. The gearbox simply cant pull the piston back all the way.

In the picture below is an example where the piston stops.

You help would be greatly appreciated.

Are you using large or mini type batteries?

Yeah, we need more details. Strength of spring, battery type/size, gears being used, etc.

You batteries maybe on there way to the garbage bin is my best guess. Since its able to fire at first, meaning that the spring isnt to long so its unable to compress it all the way back.

Try new batteries I'm almost sure that's why its seizing after a few shots, that its drains the little juice you have left in you battery then doesnt have enough to make the next cycle.

does the gearbox strain when it does shoot?
maybe the Ball bearing spring guide along with the ball bearing piston head are taking up too much room and jamming the piston when the spring is fully compressed. you only need bearings on one side of the spring, on the spring guide or on the pistonhead.
try removing one of the bearing sets and see if it helps.

its a hurricane M120 --good for 375-400 fps

8.4v large, 9.6v mini...the size of the battery does not matter in this case sicne voltage is what powers it.. its not the batteries, trust me on this one.

I just cant figure this one out:/

I see what i can do about removing the bearings or making the spring smaller.

hmmm bizzare... piston locking at this emplacement is usually due to spring overlapping the spring guide, maybe throw in a non bearing spring guide

No, the batteries and what size they are make a huge difference.

But try the bearing-removal first.

-ensure that you have full juice in the batteries
-ensure your bearings are all in pllace
-ensure that the piston doesnt jam due to overlap of the spring on the spring guide

odd problem, definately looking forward to a reply once figured out watsup with it.

Try with a stock non-bearing spring guide...if it works...toss the spring guide and/or spring.

I've run into several instances where the spring didn't seem to overlap the bearing spring guide thrust plate...but it did once things got going.

Almost without exception it's been the above issue when it works for a shot or two and then jams almost fully back (some get stuck so hard that you can pull the whole thing out still compressed).

The only exceptions were due to a mis-match between the piston body and rear of the mechbox. The back end of the piston was a little wide and was jamming are the very back position. As a weird thing to do...loosening the rear screws that hold the mechbox shell together allowed it to fire so I wouldn't have to crack it open with the spring fully compressed. Shaving down the back sides of the piston body rails fixed them. Not much...but enough to jam.

Good luck.

Tys

I've had that happen before. Spring guide, spring, and piston coming out all as one piece. That's fun.

Were you using the same spring before you installed the bearing spring guide/piston head? If not and you installed it at the same time, try putting in the stock spring.

I just went through a similar problem, where i installed a modify s120 spring in my gun with the same parts you mentioned and my motor just didnt have the torque to pull it over. I tried an s110 spring, and the motor would pull it over once or twice, and then jam up just like you mentioned.

I went back to the stock spring for awhile, and it fixed the problem. I then upgraded the motor and installed the new spring, and it seemed to work fine.

Ryan

you see the gap in the mechbox?
try filing chamfers where the piston re-engages the rail
I've had 2 mechboxes lock up on me because the piston was a little loose in the grooves and got hung up where its supposed to track back onto the rail

Dynamo is right you do only need one bearing. Just on the guide. The piston is jamming on full compression because there is not enough room in there.
I have seen this plm tonnes of times. HOPE IT WORKS OUT FOR YA CHEERS.

I'd normally point this out as well as a possibility....but if the mechbox has sucessfully shot ("...it shot three times and then locked up...") already, then it's highly unlikely that there isn't enough room for the spring to compress. It'd jam on the first shot.

I do agree with Dynamo's and your comment of a single bearing stack...but I've seen/done plenty with bearings on both ends. Depends on the spring.

Below are somewhat-wild-ass-Internet-guesses....

It's locking up at the rear of the stroke...where spring pressure is at it's max. So additional power (i.e. larger battery, stronger high-torque motor, torque up gears, etc...) might power through that resistance and it'd shoot "normally". If you stick in a strong motor and hook up a good fully charged 8.4v large battery...it should easly pull that spring. If it locks up...you've got a physical interference problem.

Try only testing after you reset the mechbox with a fully charged good large battery and semi auto only

Or there's some drag/catch that it's hanging up on (i.e. shimming is a little tight, piston is rubbing a little hard somewhere, spring is physically binding). Guessing.....With a charged battery at rest...the pack puts out a good burst of power to push through that resistance (with that motor). When drained a bit (i.e. during the burst) the power drops off and the motor can't torque through the resistance. If it looses momentum at a fully compressed/slightly jammed position...it probably won't do anything regardless if you try a fresh battery or not. But most times that I've seen it lock up immediately or after just a few shots....it's a spring/spring guide/piston body fitment issue.

Best of luck,

Tys