[Jimps]

Well no matter what, I would say ditch the SHS bearings. They are GarboDookey... I use EZO J-caged bearings. They cost $40 though. Sometimes I put a bushing under the spur, but not always. Pack them with MolyKote33, or something similar. Don't think that is your issue, but a future issue maybe. I have a weird way I shim my motor grips to my receivers. I have like 3 different grips I use only. I took one of each and cut a hole in the side of the grip. I can then see where the gearbox shell is in relation to the motor grip. I take feeler gauges to measure the gap. I then cut the correct size feeler gauges to make a shim for the new corresponding grip. When I shim the bevel gear using the half shell method, I have the shim in the grip attached to the shell half. I bought a ton of cheap feeler gauges on amazon. I cut them on my band saw and use my drill press for the screw holes, motor tower, and notches. I got a jig made, so it is not as much work as it sounds. This way I don't have a gap between my motor grip and receiver. I also know the bevel is set correctly in relation to the pinion.

I also slide the feeler gauge left and right to make sure the gearbox is not at an angle.

 

[Jimps]

I should probably make this its own post, but it seems like it fits with this one. The way I shim is also weird. As Ben said, using the half-shell method can have its issues. I call my method the 3/4-shell method. I have collected broken gearbox shells and cut viewing holes in the broken top shells. I have different shells for different brands of gearboxes. Like G&G puts their screws on the wrong side, so I have to use a G&G top shell when shimming G&G. E&C/Arcturus have a different-shaped shell; KWA has a different shell; and so on. I find the six top shells I have modified pretty much cover all the common current V2 shells. This Dytac shell lines up perfectly with a VFC bottom shell. I check bushing holes using a rod and dial indicator to assure everything is lined up correctly when mixing shell half brands. I use this along with the grips I cut and modified to shim every possible part in a V2 AEG. I find the bevel gear to be the most important gear to shim correctly. The shims under that one gear can make or break the entire performance and durability of an AEG. (This is just a selection of random parts to show my process. This is not an actual build, just an example.) I always use one of three grips on my builds. I have a test grip with a viewing hole cut in each of the 3 grip options. I sand and stipple most grips, though not always.

The first thing I do is put the gearbox shell into the lower receiver with all pins installed so that the gearbox is as it will be when done. I then screw on the test grip to the gearbox shell. This allows me to use feeler gauges to measure the gap between the motor grip base and gearbox shell (indicated with the red line in the above picture). The issue people who are new to tech work have is that when they shim a gearbox, they don't account for the motor grip and lower receiver not aligning correctly. This causes the motor height and bevel shimming to be off. A common solution is to shave the motor grip so the gearbox can sit flush with the grip (indicated by the green line above). What happens most times is that people shave too much, causing an ugly gap between the lower receiver and motor grip, as pictured above. My method allows me to measure the gap exactly, and I then cut/make a shim using a jig. Sometimes just the top or side of the motor grip/lower receiver is off, which causes the motor angle to be off. With a shim, I can be sure the grip is perfectly flush without the ugly gap between the receiver and motor grip. So the picture is a PTS grip; I would obviously use a new PTS grip and add the shim to the final build. (((The PTS grip above was a failed stippling attempt. It was shaved to fit a receiver already. This was my concept grip to test my method. I now have an unshaven PTS grip with a viewing hole cut in it to use as one of my test grips. All my stuff is in the shop at the field where I do work. These are all just junk parts used as an example.)))

With the shim added to the grip, I no longer need to put the gearbox in the lower receiver for shimming. I can now start the process of setting the motor height and shimming the bevel gear. With the modified top shell, I have a clear view of the pinion and bevel gear alignment. Different pinions and bevel gears require different motor height positions. I have a perfect view and can set it exactly where it needs to be. From here, I start adding shims under the bevel gear until it is at the right height. From this position, I take a pick and move the bevel up and down to get a rough idea of the amount of shims I need under the bevel. It is mostly just trial and error, though. As soon as I get the bevel at the correct height in relation to the pinion, I move on to the spur and sector gears. Motor height, grip to lower receiver, and bevel height are now all set.

Now on to the spur gear. With the height of the bevel set, I can shim the spur gear to get the maximum contact area with the bevel, leaving a small gap for any expansion of the gears while under load. I have modified offset feeler gauges to measure the gap. I can fit them in easily to measure with the cutout in the top shell. I repeat the process with the sector gear. I set the gap with the feeler gauges, but it just depends; every build is different, and sometimes you don't have much of a choice with setting the gap ideally or perfectly. I can then throw a piston in and check the sector and rack alignment. The top shell in the picture was also my concept shell. On the top shells I use now, I have a hole cut where the Titan optical sensor sits. This way I can check to make sure there is no interference between the sector and top board. I can now use the actual top shell and add shims to the top of the gears. I have never had a situation where one of the gears was shimmed too high when adding the actual top shell. I have found parts that work for me, and I stick to them. Everything is now set shimming wise. This has been very successful for me. I might have made it seem complicated, but it's really easy and quick.

I can also use this to check other parts in the gearbox. As you can see above, these random junk parts would not work well. The cylinder head is sitting flush with the gearbox at the bottom but has a gap at the top. This means all the force from the piston will be directed to a smaller point instead of spreading out over a large area. It could crack the bottom of the shell. (The cylinder head is not resting on the guide pins, but that is another thing to consider as well.) You can also see the tappet plate is not in good shape. It is past 90 degrees and will push the nozzle downward. It is also very common for tappets to not fit nozzles very well. You can see the gap between the nozzle and tappet; it is not seated all the way in. This, along with a poorly fitting nozzle to cylinder head, can cause mid-cap syndrome. If you have a well-fitting nozzle on the cylinder head, this gap is not a huge deal.

I get that this is not something most people will do, but it is how I have gotten the best performance possible. Millions of combined cycles over many rentals, DSGs, customer guns, personal guns... Like I said, I have parts I like to use because they work well for me and the builds I usually work on. There are always exceptions, and it is airsoft we are talking about. If a customer brings me all his own random parts and wants me to only use his parts, this method might not work out. He might not have the same grips I use, so I won't have a test grip for shimming this method. Maybe he has a gearbox that none of my top shells will fit on. You get what I'm saying.. Just what I do, everyone has their own way of doing things, I'm OCD when it comes to tech work, so I usually take it too far, lol. Hopefully this made sense. It makes sense to me, but I'm an idiot.