Piston in G&P M4 Spec Op

[matthewsmith]

Hi

I hope some one out there can help me.

I've had a G&P m4 spec op since March 09. I recently changed the standard barrel to a Mad Bull 6.03mm tight bore barrel to improve accuracy, range, etc.

Since I changed this I've stripped the original piston. It was then changed to a Classic Army piston which was stripped again and now a TM piston has been put in, (I'm yet to test it).

Everyone I've spoken to has said that the change of barrel shouldn't have caused a problem.

The AEG has always had a high rate of fire.

I would appreciate your thoughts guys on this.

If I change to a reinforced piston do I risk stripping the gears?

Many thanks

[The Keeper of Secrets]

Re: Piston in G&P M4 Spec Op

If you put a metal piston in youir gears will most likely go yes. You want to avoid that.

A piston is a mechanical fuse. The fact they they're being stripped means something is amiss in your gearbox. It could have been reassembled badly (no offense meant), or could have preenegaement issues due to the higher ROF.

Post up some pics of the stripped pistons and that'll help.

[matthewsmith]

Re: Piston in G&P M4 Spec Op

Many thanks for your reply.

No offense taken, I'm grateful for peoples time and help.

Could you please explain 'preenegaement issues due to the higher ROF'.

Cheers

[The Keeper of Secrets]

Re: Piston in G&P M4 Spec Op

Sure, it occurs in high rof setups.

The piston is drawn back and released.

When the piston is released, the gears now have very little resistance, and under a high speed setup will turn extremely quickly. If the spring is weak enough, and the ROF high enough, the sector gear will re-engage the piston as the piston is still travelling forward. This will cause the piston to break very quickly.

The mod to avoid this involves removing the second tooth on the piston, and you can also space the piston to correct angle of engagement.

[jagillham]

Re: Piston in G&P M4 Spec Op

Pre Engagement....

You'll need to visualise the inside of a mechbox.

As the gears spin they move the piston back (compressing the spring). When the last tooth is reached the piston then flies forward and sits at the front of the mechbox waiting to be picked up by the first gear tooth as it comes round. Bearing in mind this happens 16 - 30 times a second.

Pre engagement is when the gears are spinning so fast that once it lets go of the piston the 1st tooth is back round before the piston gets to the front of the gearbox. At that point the 1st gear tooth smacks into the piston teeth travelling the other direction towards the front still, and breaks them off.

Edit: I KNEW somebody would beat me to it, lol! :D

[The Keeper of Secrets]

Re: Piston in G&P M4 Spec Op

Ah, but your explaination was far better. Essay writing has killed my brain and I need a cup of tea

[bert uk]

Re: Piston in G&P M4 Spec Op

not sure if this helps but i stripped the piston in my old g&p m733 by putting the hop rubber in crooked,when i assembled the barrel in the hop unit i somehow twisted it causing it to twist the rubber out of shape...concequently the bb's got jammed against it...the piston couldnt go anywhere and....grind rend etc....damn!!

[sj_asc]

Re: Piston in G&P M4 Spec Op

Like said, do you have any pictures of the failed Pistons? or at least where did they fail? Did multiple teeth get stripped from the release end of the rack, or was the chunky pickup tooth ripped clean off?
I suspect the last one, in which case you won't be needing another piston if you already have the Marui.