Prowin 8mm & Prometheus Standard Gears Issue

[colonel_kipper]

Hi,
I've recently built a Magpul-inspired M4 with a Pro-Win 8mm V2 gearbox (the latest generation, black anodized). I had very few problems installing it into the lower, with only minor filing required to allow channeling of wires. I spent two days building the lower, shimming the gearset perfectly and breaking the gears and motor in. Having built the gearbox, within 500 rounds the last tooth on the Prometheus sector gear has sheared off. The piston travels freely along the guide rails and the AOE has been corrected. Despite this, the piston is already showing alarming wear, suggesting that the AOE has changed as the gearbox was placed under load.

What causes a brand new $130 gearset to break within 500 rounds? Sadly, I suspect it was due to a casting imperfection; the break is clean and crystalline. However, this may not be the case - I'm probably missing something out!

This is not the only problem I have encountered; the gun is also misfeeding on semi - rounds simply roll out of the barrel occasionally. This must be a feed nozzle/tappet issue. I have checked everything over and there are no problems I can detect.

Parts list :

Pro-Win 8mm v2
Prometheus Spring guide
Prometheus Hard Piston
Prometheus Torque Gears
Prometheus Anti-Reversal Latch
Prometheus MS 100 (relatively weak)
Systema rear wiring loom
Systema M4A1 feed nozzle
Systema Magnum Motor
Systema Chrome Molybdenum Pinion Gear
Kanzen Ceramic bearings 8mm
Mosfet *not AB*
G&P EP Power 11.1v 1500mah 15c Lipo

I've already spend $2000+ on this build, and so to be left with a paperweight is more than frustrating.


Thanks in advance.

[ILLusion]

When the gearset broke, were you by any chance firing in full auto?

Based on your setup and description of damage/wear, I'd say your ROF was actually too high for the applied spring. It sounds like your sector gear slammed in to the piston as it was still moving forward back in to battery, causing the tooth to shear off from the stress.

[Dynamo]

make sure you have the roll pin holding the cylinder head in place.
mine had fallen out and i didnt notice untill i blew a gear set and piston. lost half the teeth on the sector gear.

[glancy]

i buy this gearbox. Where? PM me,thx

[colonel_kipper]

Illusion,
Unfortunately I was alternating between semi-auto and auto bursts as I was testing the gearbox out. The MS-100 is not a hard spring but has been used with great success in a HK416 which was running at 40 RPS; I am really baffled by this - the gears were broken in and run with a soft spring, and there is no evidence of premature engagement on the piston.

Dynamo,
I have checked this over and it is fine - I put loctite on all roll pins and hex screws. Thanks though, I wouldn't have considered that!

Glancy - Pm inbound. If you're looking for one, I believe they are out of production now but I've seen them in several stores in HK.

However, I was thinking that not all is lost - If I remove one of the metal teeth (the last tooth) on the piston, then shouldn't the gun function with no problems (except for slightly reduced FPS as a result of less spring compression)?

Thanks!

[ILLusion]

The type of damage I'm referring to comes from full auto use, or even two consecutive shots with TOO HIGH RPM.

It's exacerbated by the fact that you have an MS100SP spring (which you admit is a soft spring - THAT is the issue... it's softness. It doesn't matter if it worked with an HK416), combined with a 11.1v battery (which performs faster than a 12v Ni-Cad/Ni-MH) AND a Systema Magnum motor which increases ROF even more.

Here's a basic description of what's happening:

Your gearset is spinning WAAAAAY too fast for the spring to keep up. Because it's a soft spring, it returns the piston to battery a bit slower, and as a result, the piston ends up slamming in to the sector gear teeth which have already begun swinging around on their next rotation. Two opposing forces moving against each other generally aren't a good thing... it's worse when it's teeth meeting in mid-engagement, because it's probably already raked a couple of teeth or more till it finally caught one), and if the sector gear DOES catch a tooth on the piston (maybe one or two teeth prematurely), it will send the piston to the back, and once it reaches the back, the piston's last tooth will release the piston... the problem is, assuming the sector gear caught the piston one or two teeth early, then that means there will be one or two teeth left in it's rotation. So guess what happens? The piston starts it's return forward, but rather than going for a full stroke, it meets the first of the two remaining teeth on the sector gear... it survives... sorta... bruised and a bit damaged... probably raked one or two teeth on the way, the piston pulls to the back again, releases as the tooth clears, and WHACK. Smacks in to the second tooth and repeat.

It could be happening with more teeth... or just one tooth. Hard to say. But your part list is the perfect recipe for this type of disaster, and your described damage sounds like the result of this type of damage. This is why there's so much damage across all your piston teeth, but only the last one or two teeth of the sector gear have damage. Check the first one or two teeth of the sector gear as well... there may be some premature wear on there as well, while all the middle teeth should look okay.

As far as removing the last tooth of the piston... that will only work if you also equally remove a tooth off your sector gear. Otherwise, FOR SURE the piston will slam in to the last remaining tooth of the sector gear, because the sector gear will then ALWAYS release the last tooth of the piston with one tooth left in the rotation.
Yes, you'll get slightly lowered velocity due to the short stroke... but this is only if you are running with a full unported cylinder.

[colonel_kipper]

Hi Illusion,
I appreciate the explanation, and understand that this is the most probable cause, but it seems odd that the HK416 I referred to was running an MS 100, Systema Turbo motor, 14.4v Lipo (2500mah) and Systema High Speed gears, yet I didn't encounter this problem! I must have just been lucky! So, with your excellent explanation in mind, what would you suggest might resolve this issue?
Thanks!

[ILLusion]

Are there any differences in the cylinder porting? Or are they both the exact same type?

[colonel_kipper]

Actually, now that I think of it, the '416 was running a ported cylinder and I used the stock full (unported) cylinder which came with the Pro-Win, even though I'm using a Systema MC51 6.04mm barrel (285mm) in a 10.5" upper.

Update : Pictures!

Sector gear damage



Piston teeth damage





Here is another interesting area of damage - the cylinder has been struck by something (I hope not the sector teeth) and deformed - Should it be replaced, and how can I avoid this. Do you think it might have been caused by incorrect disassembly, or not releasing the anti-reversal latch before separating the upper from the lower?





Thanks!

[Sha Do]

Wow, excellent pics....they will surely help the ILLusion man with you diagnosis. As for the cylinder damage, the pre release of the anti revers latch is not the problem. As far as I can see, it appears that the sector gear tooth that broke off (or some foreign metal object) got slammed between the piston teeth and the cylinder on the forward stroke of the piston. This could also have caused the damage to the piston teeth indicated in the pictures.

SHA DO

[Amos]

Well.. if you ever want to short stroke something you've got a sector gear!

Illusion's suggestion is what I'm thinking it is, with the full cylinder installed in your gun the piston's not returning to rest fast enough (due to the build up of pressure from a BB in the barrel)

That set-up would work with a higher rated spring... or if you said you had a similar set-up that worked with a ported cylinder... I'd try that step.

I would advise changing out the cylinder, you could try straightening it out, but there has most likely been damage to the interior coating if it has one... (I had no idea what Pro-win cylinder's are like)

[colonel_kipper]

Excellent, I can't thank you all enough for your input, I'd be helpless otherwise!

So, things to do tomorrow:

1) Replace cylinder with ported counterpart
2) Potentially replace sector gear or remove last metal tooth from Piston rail
3) Examine rest of piston body and teeth ( I suspect there may be wear on the metal rail section of the piston rack)
4) Replace piston with new Prometheus Hard Piston ($30 wasted!)
5) Replace Tappet Plate (There is some deformation of the tappet plate caused by the sector gear nub engaging either at high speeds, or because of the broken sector gear tooth interfering)
6) Replace feed nozzle with PGC original Illusion - Does the Prowin have a proprietary feed nozzle length? I stupidly assumed that because the gearbox is for an M4, it uses an M4 length nozzle and so a Systema counterpart was installed in the first build - could this be causing semi-auto problems and other feeding issues, such as rounds rolling out of the barrel and shattering?
7) May install AB Mosfet for testing

Any ideas between now and then would be greatly appreciated.

Thanks!

[Dynamo]

Originally Posted by colonel_kipper

6) Replace feed nozzle with PGC original Illusion - Does the Prowin have a proprietary feed nozzle length? I stupidly assumed that because the gearbox is for an M4, it uses an M4 length nozzle and so a Systema counterpart was installed in the first build - could this be causing semi-auto problems and other feeding issues, such as rounds rolling out of the barrel and shattering?Thanks!

just a heads up, the nozzle included with the prowin gear box is 0.3-0.5mm too long. i had all sorts of feeding issues with the stock nozzle. some of the issues were chopped BBs, BBs rolling out of the barrel, and BBs getting jammed due to them having to squeeze past the nozzle taking the lower lip of the hopup with it. after switching to a Modify M4 airseal nozzle, i have had no more feeding issues at all. im running the prowin in my VFC416 with a 11.1v lipo, so any feeding problems generally ended up with a stripped piston. and as i think back i did have issues with a non-ported cylinder. with a high speed setup you need to make sure your piston can return to full battery before the sector gear re-engages it, if not you will keep stripping pistons and gears.

[ILLusion]

The full cylinder could have been a huge cause of your problems, because the compression is slowed at the beginning and doesn't reach terminal velocity till after the projectile leaves. If you're using a shorter barrel, I'd highly recommend getting a proper cylinder (Type 2).

Regarding the cylinder damage, I'm with Sha Do on his assessment... I'm also inclined to think that it was the sheared sector gear tooth dinging the cylinder.

My suggestion:

1. Replace your cylinder with a type 2 cylinder
2. Stick with your gear set
3. If your piston tooth rack is mangled to the point of no more function, then replace it. No need to remove the last tooth on it, since the piston will already release once the last sector gear tooth passes. Although... you could still remove that last tooth if you wanted to save that 0.1 grams on weight so that the piston picks up speed that much faster... lol.

Tappet plate wear is possible from the high ROF. I'd keep several on hand if I were you. If you don't have any domestic sources for the tappet plate, give me a shout. I have two spare ones lying around here that aren't moving, so I can see if I can dump it to you at a good price. Hit me by PM if you want it.

Regarding the feed nozzle, I've never used the ProWin one before. I always replaced it with aftermarket ones, so I can't comment on that. If you are having feeding problems such as the BB not shooting, even though it's been loaded, this can also be a cause of your problems. If the BB is stuck behind the hop up rubber (the Pro-Win white hop up rubber is notorious for being too stiff and causing this), and if your air seal is quite good, a BB stuck behind the hop up rubber can actually cause the piston to return to battery very slowly and/or will not come to a complete rest, which will mean that for sure the sector gear will slam in to the tooth rack before the piston is ready to accept it.
Dynamo covered this issue as well.

[Dynamo]

i had to use the unjamming rod to force the BBs off the hop-up. after changing nozzles i no longer had any problems.
and Illusion is right about the hop-up rubbers that come with the kit. the opening is far too tight.