[Ettus]

I have been working on a high-ish rps V2 aeg build from scrap parts for about a month now and have come across an issue that I can't seem to find a solution to. I have been working on guns for several years now and have built multiple field rifles as well as dmr's and wanted to try my hand to see what I could learn from doing a higher rps ssg build. I have got compression and all the other basics nailed down in in the build but for some reason keep getting super rapid wear on my bevel gears ~1000 cycles. Shimming done pinion to bevel exactly as outlined in TheAirsoftTech's youtube guide, as I've been doing for years now. Motor alignment has been checked using the alignment checker from Brill armory and is dead on, measured with digital calipers. I've been racking my brain over what could be causing this for about 3 weeks now and would love to know if anybody here has any ideas before I scrap it and just dmr the gun. First picture is shs 10 tooth and g&g stock 10 tooth, second picture is the shs again, 3rd picture is unknown stock bevel, and 4th pic is another g&g 10 tooth. Thanks.

Complete GB build list:
Rocket 16 tooth steel rack piston SS by 3 teeth with 2nd tooth shaved down for aoe
Shs 12:1 gearset SS by 3 teeth on pickup
Lonex V2 tappet plate
Shs bearings, steel bushings on spur
Vfc oem antireveral
Retro arms QC spring guide
M130 main spring
Rocket airsoft cylinder head
Zci air nozzle
Krytac stock 3/4 ported cylinder
Microswitch trigger
Gate warfet, no AB, rof 100%, 0 precocking
Shs HT 16 tpa motor
JG QC GB shell

395~398 fps at 28 rps 11.1v 35c

 

[Ettus]

Here are some more pictures. The grub screws on the top of the motor grip are my latest attempt to correct this issue, was shredding bevels before installing them. I noticed that the shs bevel and the no name bevel seemed to suggest the motor height was too high as well. If it would be beneficial I can take the gearbox apart and get a picture of the current bevel gear's teeth as well. Could you elaborate a bit more on what you mean by shimming to have a .3 ~.5 mm gap, my interpretation would be the play in the gear, side to side? Also, any ideas on how to check for bevel gear centering in the case? I'm a senior in mechanical engineering so feel free to get extremely technical if needed lol. Thanks again.

Something else that may be beneficial to know, measured amp draw on the gun currently is 16 amps continuous, not sure of accuracy of my tester's peak measurement however, so not included.

 

[Ettus]

I need a photo of the pinion too.

Keep in mind not every pinion fits every bevel. But something else is off by a lot. The tips of the bevel teeth aren't as worth. Suggesting the motor height is way too high. A pinion with fatter teeth basically needs to sit edge to edge with the bevel. Thinner teeth pinions will set higher where you can't see the edge of the pinion teeth. After than you shim the pinion bevel tight but with a .3mm to .5mm gap.

If the shell bottom is ground improperly it can seat the grip off. The grip should be sanded so it doesn't rest all its pressure on the lower receiver and sits flush on the gearbox, unless the receiver is a better fit than the gearbox, which happens. The grip hole should not touch the motor tower first, the motor tower should contact the gearbox hole first. This will screw up the motor angle checker tool.

Another thing, a ton if gearbox shell manufacturers modified molds to make their 6mm or 7mm gearboxes into 8mm gearboxes. Because of this some brands poorly centered the hole and the bushing or bearing will sit off center, making the pinion wreck the bevel as it's not lined up. Even some high end cnced gearboxes such as the beloved retro arms shells have improper 8mm bearing holes due to inability to properly design a gearbox for some reason. So if your bushing/bearing is off it would cause insane wear like this, and the gearbox/motor grip would clamp down on the angle tester giving a false impression its passing the test.
View attachment 282560

The gearbox itself could also be sitting back tilting. Either due to fitment or other issues. If the grip is resting on the lower but the gearbox is tilted back from fitment issues or tightening the stock screw first it will cause alignment issues.

Best of luck.

Oh and this wear has nothing to do with the spring, rps or anything. I have plenty of high rps builds running every weekend that have very little wear on the bevel and pinion. You will likely see a rps improvement once you fix this issue and the aeg will become super quiet.

I also wanted to go ahead and include a video of the gun cycling, just to help familiarize you with this particular case as much as possible.

Rapid bevel wear issue build

 

[Ettus]

Well keep in mind, some motors don't fit the same at all and will push the motor way to high regardless of how much you lower it. Shimming the motor armature or sanding the endbell of the motor can help, but you need to know what your correcting if you do this. Some grip caps fit weirdly with some motor endbells too. The motor tower also needs to be shimmed snug into the gearbox hole. If its sloppy it will wear things out.

I shim completely differently than anyone else. So it's hard to recommend how to check shimming without literally writing a guide on how I do it. But you have something way off and it's screwing you over. I'll give it more thought and post back here if I can think of anything else.

Sounds good, thank you much. I'll take the gearbox apart sometime tomorrow after I'm done with classes and send a few pics of it in the "half shell" configuration to see if you notice anything I'm missing. Looking at the way the gear is worn, it almost looks like the grip needs to be canted further forward toward the magwell as i kinda looks like the pinion teeth are slapping into the top of the bevels teeth, increasingly so closer to the edge, rather than slotting into the next gap on the bevel like it should. Ill

 

[Ettus]

First, I want to say thank you to all you that have taken the time to post and try to help me out with this issue. That said, there has been some great ideas about what the issue may be and I was wondering if any of you think this could be caused by PME? Previous bevel gears were ruined with the gun SSd by 2 teeth rather than the current 3 and using an sp120 rather than m130.

I have opened the case and double checked my shimming of the gears and to the absolute best of my knowledge they are as good as I can get them with this shell, about 0.1~0.15 mm vertical play in each and getting roughly a dozen revolutions spinning with finger from cylinder window, with superlube. I haven't changed any of the shimming from what it was previously.

I assembled the gb with only the wiring and another loner g&g bevel gear I don't care about and installed the motor as it would be on the rifle and but left the grip screws loose so I could play around with angles. I then trial and errored moving the motor grip around forward and backwards to find where it was the absolute quietest I could get it (basically just plain motor whiring but a little louder) and had a friend mark the perimeter of the grip with a sharpie while I held it. I then shimmed the grip to match this line when screwed in tight. I followed a similar procedure with the motor height. I then marked the teeth of both the bevel and pinion with a blue sharpie like one would when sharpening a knife to check for uneven wear, and so far, no signs of uneven wear. I will continue to monitor for any wear, but I think this may have worked for me and wanted to share. Included are pictures of the bevel and pinion after running about 100~200 cycles with everything installed.

 

[Ettus]

PME isn't a bevel and pinion issue. It's a piston and sector gear issue. ie...the sector is coming around to pick up the piston before the piston has fully made it forward to the resting state.

Plus a SP120 is the same as a M130 and unless you are running an insane DSG...you shouldn't be PME'ing with these springs at all.

That's what I figured, I know that pme is a sector and piston thing, but I thought maybe it could be a "weakest link" type deal with the bevel teeth being the smallest and thinnest in the gb with nowhere to go due to the ar latch, causing it to fail as I've seen the bottom teeth of the bevel in poorly shimmed GB's as well as spurs fail due to pme (I could hear it right before the guys gun broke, super light spring~m90, at least 25 rps) Thanks for the info on the springs. I actually saw a 25 fps difference in the m130's favor swapping from the sp120, which is why I swapped it, both were new.

 

[Ettus]

M130 short stroked 3 can hit like 38 with a long 6.01 and 42 with a long 6.03 with a .28 bb. Lighter bbs or shorter barrel means even higher pme ceiling.

This isn't pme wear. Pme wear is mostly on the piston then sometimes a broken shaft or tooth. But not the part that touches the pinion.

Ok, cool, it was just a thought I wanted to run by you guys to see if it was feasible. I'm running .32g BLS bios at the moment since they're the lightest I have, just for reference.

 

[Ettus]

Another thing. American Consumerism Does Not Apply in Airsoft.

There are no standards in this industry just a guide line that is loosely followed at best. A true M130 out of the package is not that common. The only way to get this is if you buy a hard spring and the rating is true, like from a Japanese supplier.

Unlike a M130 made from a soft alloy where it needs time to settle to the M130 rating. Thus you overstress your mechbox and it gives you a false positive until the springs settle. This was the issue with SystemA springs from 23 years ago. It took the spring about 2-3 weeks in a compressed state to "settle" down to their spring rate. When newly installed a M100 shot like a M120...people were like WTF? Maker never mentioned that you had to compress it to settle it. Events like Savage Garden 3 really messed users up because they thought they installed a M100, but when they chrono'd they were 40fps over..."but I bought a M100"...

Then you just have low end makers like Matrix Springs which is a Evike House Brand...they are just bad. I mean...who would buy a spring that has a FPS rating like this:

235% (M130) ~420~500 F.P.S.

Sadly...thousands...a M130 should never hit 500fps. That is a M150...but the alloy...soft...cheap...and end users not know the details of the spring...

Oh yeah, I definitely get that. I don't think I've ever had a part just "drop in" without needing at the very least a little sanding or filing, excluding oem replacements.

 

[Ettus]

Very late on this, but just wanted to give everybody who helped out a big thank you for all of the shimming insight as well as to give an update/final build details. I seem to have fixed the issue by discovering that the armerature it's self on my SHS HT was ever so slightly bent.The JG shell also ended up developing cracks in the lower part of the cylinder window so I went ahead and picked up a Retro arms shell from Brill to also eliminate the variable of the bushing holes being off spec at the same time. After getting a new motor, I double checked my motor angle with the Brill tool by comparing the result with my krytac's motor angle and matching it. So far about 2,500 cycles in with no obvious signs of wear on neither the bevel nor pinion on a m130 SS'd 3 teeth running at 32 rps @380fps +/- 2. On 11.1v 30c lion battery. Again, thank you all for your input and knowledge, I'll be sure to put it all to good use in the future and, hopefully, it will help somebody else down the road.

 

[Ettus]

Lipo or ion battery? No such thing as a 30C ion pack, it might claim to be but it is not. Lipo battery is really superior in every way.

Honestly, I'm not even sure, thats just what it says on the pack, maybe its 30c burst rather than continuous. It's one of those crummy matrix batteries from evike that I bought when I was young and first getting into airsoft and didn't know any better. It seems to last pretty well though. I like the rof and trigger response it gives so it works well enough.

 

[Ettus]

Good to hear things have worked out! BUT...

Not to burst your bubble, but RA shells are known to have off-spec bushing holes as documented here by a few members. Yours may or may not have this issue, but just wanted to bring it to your attention.

Yeah, I think somebody previously said something about that in this thread, maybe it was Ben. I'll definitely keep an eye on it. I think RA might have actually acknowledged and supposedly remedied this in their newest generation (I guess that's the right word) of shells in their product notes on their website (I think).