help me find a piston !!

[BeAcH]

Hey everyone,

Some history to start off with. I have broken two pistons now, the first piston

that came with the king arms m120 V2 mechbox i broke it in half in about

2500 bb's. So i bought a prometheus hard piston and today after about 1000

bb's my m4 stopped working. So brought it home, ripped it all apart and upon

investigation i noticed that their were no teeth left on the piston.

I like the piston design and body strength that the prometheus hard piston

has, but i need metal teeth to help prevent this from happening. So what

kind of piston does ASC recommend that i try next?

I am using 7.4v 20c lipo and 11.1v 20c lipo batteries with ultra deans

connectors, modify torque up gear set with the nano-class treatment.

cheers
beach

[Styrak]

Stop using lipos, is the solution. Or use a lower powered lipo like a 15C.

[lurkingknight]

find documentation on proper AoE correction. sorbo and first/second tooth removal, should help a lot. If you're stripping teeth you have an issue called pre engagement, the timing is screwed up if you're using higher power batteries though imo 20C is not really that high powered. What's happening is that your gears are doing more than one cycle while your piston is only doing 1 so before the piston returns to the front, the sector gear is already in the middle of another cycle.

You need a lighter piston assembly and you need to fix the AoE so the pickup tooth is the only tooth that gets hit by the sector gear even if in mid cycle. A full metal tooth piston will be stronger, but I think the prommy hard piston ( I haven't checked) is a metal piston which makes it heavier.

I'm using an SHS full metal rack and 2 CA blue pistons with metal racks in my aegs, I don't even have a full aoe correction done and I have not blown anything up, using 20C and 25C 7.4s and 11.1s. Though I am running computerized mosfets and only running 60% motor speed when I have the 11.1v in. I have run the guns for a few hundred rounds at 100% speed with no ill effects.

[phloudernow]

whoa dudeeeeeeee what power are you running at, i have no idea how you stripped a prometheus hard piston, ive had a high speed set up shooting about 320 FPS and the gearbox has been running strong for 4 years with over 20000 rounds through it. only thing ive done is regrease the gearbox every year. all parts are working 100%

I short stroked the piston for a faster rate of fire and it works great with my KA 11.1v Lipo

[iKliiu]

SHS pistons are great for both high FPS and ROF. But like lurkingknight said, AOE is crucial if you want your piston to survive.

[BeAcH]

thanks for the advice so far guys,

on the prometheus hard piston i removed the second tooth so the sector gear would have full/proper engagement, ya i couldnt believe what i saw when i looked at the teeth on the piston. im using a m130 spring, modify torque up gear set and a eg700 motor with 7.4 or 11.1 lipos, im not even that heavy on the trigger. Its mostly semi auto shooting that i do.....bad luck, im going to try this piston next Modify Quantum Piston....what do u guys think?

[phloudernow]

dude... if you going to be running anything over an m120 u need metal teeth.... prometheus piston is more meant for high speed low powered set ups and they work beautifully.

[iKliiu]

M130 is not high at all for a Prometheus hard. Also, just because the second last tooth is removed doesn't mean AOE is corrected. You really want the sector gear pulling the piston back at around 12:30.

As for the Modify piston, I would skip that and get this instead. No need to spend over $20 on a piston, IMO.

[Maethori]

Originally Posted by iKliiu

As for the Modify piston, I would skip that and get this instead. No need to spend over $20 on a piston, IMO.

Maybe true, but the Modify Quantum piston is really nice. I have it in two of my guns.

[ThunderCactus]

Prometheus pistons are tanks, but you have to use them with prometheus gears

The only time I've ever heard of anyone stripping prommy pistons, it was on somebody else's gearset. These pistons are supposed to go all the way up to 600fps (allegedly) or at least 1500rpm at 400fps. That's why prommy makes infinite torque/high speed gearsets and only ONE type of piston.

Your problem is elsewhere, as stated, probably just need to remove the second tooth since it's cycling too fast to engage properly on the first. If you switch to an all metal tooth piston right now without solving your issue first, I promise you're just going to wreck something else that costs more than a piston in the gun.

[BeAcH]

thanks for the helpfull advice,

How can a guy ensure that his mechbox is in the proper angle of engagement?

-remove second tooth off of piston

-make sure the sector gear contacts the piston at 12:30 position on a clock, just a little forward of center ?

-i dont want a repeat of this, so if im missing anything please let me know....i think im just going to stick with the 7.4 lipo too, i dont need a high cyclic rate.

cheers.

[lurkingknight]

some also remove a portion of the 3rd tooth as well.

you can correct the engagement position by putting nylon washers between the piston and piston head, but sorbo is generally a better choice since it also reduces shock at the front of the gearbox (good for V2s), but you will lose a few fps either method as you will effectively reduce volume of air in the cylinder. It depends on how far you are out of the sweet spot. maybe a single washer will do... maybe a piece of sorbo will do, or you may need sorbo AND a washer. Best to measure how far out you are from 12-12:30. sorbo comes in different thicknesses.

You also need to determine why your piston cycle is slow. Is it because of low spring power or weight. A 120 should be fine in terms of energy to return the piston forward, so it has to be the piston travel is slowed by something, either drag/friction or weight. If you can't adjust those any more, then you need to adjust battery strength or regulate the cycle speed of your gears with a computerized mosfet.