DISCLAIMER!!!!!!!!!!!

I used this method to shim my gun today, and it has worked great. However, problems from shimming can sometimes only be visible months down the road, so yeah. I have a big game on Sunday, I'll report on problems and successes then, and again in a few weeks/months when I switch piston heads.


Sorry for the lack of photos, just use your imagination :)





So I've been working on the ol' mechbox lately, and realized just how vague many of the shimming guides are on details, so I decided to post a detail rich guide on how I shimmed. I was able to shim my correctly (I hope) in only about an hour or so. I was surprised to find that the gears spun so well with so little time and effort spent, since the vast majority of shim guides talk about how arduous shimming is and claims that 12 hours are required to do the job right. Anyway, on to the methods. I'm assuming you are already familiar with gearbox internals; if you are not, please familiarize yourself with unfamiliar terms and parts.


So on to some details: This was with a TM V2 box for my SG1.

So, let's assume you already pulled out the box, stripped it of all its parts, and have washed it clean of all the old, dirty lube.

Pop in whatever bushings you will be using. Use a small amount of lube to fix them into the gearbox shell only if you are being annoyed by them falling out of place.



So now that prep is done, it's time to shim. YAY!


Grab your spur gear, and set it into place in the left half of the gearbox shell (if you don't understand what I mean by left half, I mean the part that would be to the left if it was in your gun and you were aiming at a newbie). Spin it and watch to see how close it is to the shell; the gear should have long part of the axel pointing out towards you. If you can spin the gear without it touching the box, no need to use any shims. Otherwise, start with a 0.1mm shim and move up until the gear can spin without hitting the box.

Next, the bevel gear. Put it in to place so that the small part of it fits face down, making contact with the spur gear you just placed. Now, look very carefully at how the two gears interact. Spin them a little, and pay close attention to how they act and make contact. If it looks like the bevel gear is sitting on the spur gear, add 0.1mm worth of shims to it until it JUST clears it. Feel free to consolidate shims as well; no reason to use two 0.1mm shims when you could use a 0.2mm. Anyway, test spin after shimming the bevel gear, and if the two gears spin well together, it's time to move on.

Finally, the sector gear. Place it so that it meshes with the spur gear, and just like the bevel gear, observe the fit before adding any shims. If it looks to be resting on the spur gear instead of meshing with it, shim it up like you did the bevel gear. If it looks like it is floating above the spur gear, remove all the gears and add 0.1mm of shims to the bevel and sector gear. Once it looks like everything is meshing without resting on each other, try some test spins. If you have done it right so far, the gears should move with little effort.

But wait, you aren't done yet! Now, put the right half of the gearbox shell (complete with bushings) in to place, and while gripping the back part (where the spring guide would reside) and the base (where the bevel gear makes contact with the motor), try to spin the sector gear. Don't force it, try to gently spin it. If it spins freely, go right to the next paragraph. If it does not spin freely, try to look inside and/or listen to where the friction is coming from. If you can't see it or find it, lube the gear teeth (except the teeth on the sector gear that are meant for the piston) and try to spin again. This time, if it still won't spin well, open the box and look for where lube is that is not where it should be; that is where the gear was making contact. If that is on the left side of the gearbox shell, add 0.1mm of shim to every gear, and try again. If it is on the right side of the box, add 0.1mm of shim on the troublesome gear, repeating as necessary until the gears spin freely. Now, when I say spin freely, I simply mean that when you try to spin the gear, it moves pretty well, and with none of that grinding noise that comes from rubbing the side of the box or another gear the wrong way. If you don't know if it's spinning freely, randomly add 0.5mm worth of shim to a gear and see what it's like to have it lock up, and use that for a baseline of what sucking is :)

So yeah, your gears are in the box and are spinning nicely. You still are not done yet. Spin those gears, and pay attention to what the bushings and axels do. If they move, note about how much. If they do not move, push on them a bit and see how much they move on you. Pay attention to how much they move, and how the spinning is effected by them moving. An example: I found that the bushing to my bevel gear did not move at all, even when I pushed on it, while the bushings to my sector and spur gears moved quite a bit. I also noticed that they both wanted to move to the left side of the gearbox shell, and that they didn't spin well when I pushed them to the right. I think you see where I'm going next....

Open the box up again, and add the approximate amount of shims you need to make the bushings stop moving once the box is closed. If you can't tell how much to add, start with 0.1mm and work your way up. If you add 0.1mm worth of shim and it locks up or does not spin as well let it be. If the bushings move less than 0.1mm, let them be. You don't want to shim them too tightly, and using this method, you should end up adding only just enough. Now, once you have found your money combo, read the next paragraph.

Great job so far, but screws do a much better job holding your gearbox together than your hands do, so in order to check your job so far, you need to add at least 4 screws. Place them so they form a "x" across the gear housing section of the gearbox shell, although it will look more like a cross. After you have added the screws, check the spinning again; it should be unaffected if you have done a good job. Watch the bushings again, and make sure that pushing on them results in less than 0.1mm worth of movement and has no or very little effect on the ability for the gears to spin. If everything checks out, congratulations on a great shim job well done; now put the mechbox back together and enjoy.





Feel free to offer comments, if I screwed something up, I'd like to know ASAP ;)

I'll get some hi-res photos for you tommorow, as I have nothing better to do.

I love how you two have virtually the same avatars and Ralph is making guides just like you, Krytik!

Good job with the guide. Some mod should pin this...after the pictures are up.

Just wanted to put up a little update. I did some hard core airsofting yesturday and so far everything held up very, very well. So far so good!

Yeah, it's all a conspiracy, Kryptik = Ralph.

I can't believe I just said that...oh snap, I mean...uh.....POST #400!!!