Piston stuck in the back of the mechbox.

[Omi-san]

I'm in the process of downgrading a M4 to bring it under 350fps.

I changed the PDI 140% for a stock TM spring. Now when I pull the trigger, the piston gets pulled all the way back and remains there.

I don't understand what is causing this. I tried different pistons and spring guides. The gears and anti-reversal are all in place, so is the tappet plate. Everything looks normal to me.

Is the stock TM spring the problem?

[TokyoSeven]

Is the spring bent at all? Like is there a curve? Or perhaps the spring is to short? I remeber I had a spring that was to short, it would compress, but not that well, and often the piston would lock back because of it. I wish I could offer more information, but the only thing that remedied my issue was using a diffrent spring.

[Omi-san]

The spring looks normal. Even with the stock TM piston and spring guide, it still locks up. It makes no sense.

[Double Tapper]

Is the gear timing setup correct,is the piston in the groove guides?.
This happened to me a few times.Then found out the hop up was
jaming the BB's and cuasing back presure to cause the piston to
fall off the timing and jam to the rear.

[Omi-san]

Originally Posted by Double Tapper

Is the gear timing setup correct,is the piston in the groove guides?.
This happened to me a few times.Then found out the hop up was
jaming the BB's and cuasing back presure to cause the piston to
fall off the timing and jam to the rear.

The gears and tappet plate are properly set before I close the mechbox. the piston is in the grooves too (the mechbox wouldn't close otherwise?).

[TokyoSeven]

What do you have for gears? Just the stock ones?

[Double Tapper]

I had the piston off on one side and mech box with no problems,when it gets to the
rear it jams also.It was something I overlooked when reassembling the box.

[Omi-san]

Systema all helical, but the kind that works with a normal piston.

Could my problem be related to the fact to that stock spring was attached to the inside of the TM piston before I pulled it out?

[TokyoSeven]

As in it still has that little hook dealy that stock TM springs come with?
Did you reinstall it with the unique piston head attachment that holds the piston head onto the piston but also holds spring in properly as well?

I would have to say it was the gears and the piston combo, but you say that its suppose to work with regular pistons.

Whats the motor?

I dont know how or why but Im seeing this image in my head. Since there is a weaker spring, Im seeing the gears driving the piston back with alot of force but returning to their standard position before the piston can be pushed back into the cylinder by the spring, so the piston trys to come back forward but is caught on the gears.

[Omi-san]

Motor is EG 1000. The gears have a normal ratio.

By playing around with the TM spring and a Prometheus ms110, it's clear the TM spring is a bit larger and doesn't slide smoothly inside the piston. That might be the problem.

Should I put the PDI 140% back in, but cut a few coils away? Or else I'll need to order a stupid 300 fps spring from HK.

[Renegade)]

Is it only jamming with that stock spring?

[TokyoSeven]

Originally Posted by Omi-san

Motor is EG 1000. The gears have a normal ratio.

By playing around with the TM spring and a Prometheus ms110, it's clear the TM spring is a bit larger and doesn't slide smoothly inside the piston. That might be the problem.

Should I put the PDI 140% back in, but cut a few coils away? Or else I'll need to order a stupid 300 fps spring from HK.

Cutting coils is always an option but honesly I would just order another spring, or see if a friend has one they can loan or sell you for the time being.
When you cut a spring, you have to makes sure you do a clean job of it and file the end cause you wouldnt want to scratch up the inside of the piston.

I believe there is a demon in your mechbox. An excorcism using Franks Red Hot and forceps is in order.

[Cobrajr122]

May be a Muzzle Velocity Reducer will work instead of downgrading the internals.

Testing with G36C
Original - 82.1m/s - reduce 0%
Yellow - 67.1m/s - reduce 20%
Red - 52.5m/s - reduce 37%
Blue - 48.4m/s - reduce 42%
White - 44.2m/s - reduce 47%

[Styrak]

You could try these, hell of a deal:

http://airsoftglobal.com/product_inf...oducts_id=6756