Have I shimmed correctly?

I have recently shimmed (or attempted to) my gel blaster. I have not been to any games yet or heard blasters other than my own fire. I have made my first attempt at shimming a blaster, and want to see what everyone on the forum thinks about how my blaster sounds. I thought it was very high pitched, and have considered reshimming it but want to make sure it is necessary before I pulled it apart.

Metal gears 7.4


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It can scary shimming for the first time hey…

I listened to your vid but it’s hard to tell ay.

You can sort of check it without opening the gb, there’s a few indicators…

Shake the GB, is anything moving…

Poke the shafts of the gears, any movement…

Using the shell window next to the bevel gear… try poking something in and turning the gears, should be turnable…

Same window with motor/grip on, ensure there’s a lil “knock” (pinion and bevel have a weeeeee gap between them…

Good luck

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Thanks for the input and the luck

Nothing seemed to be rattling and the shafts seemed in place, unfortunately is a classic army gearbox so it doesn’t have much in the way of windows, but everything seems ok. If anything I was worried about putting too many shims on, and if this would cause any damage to the blaster.

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It does sound a bit tight in there :thinking:
You could try and adjust the motor slightly and listen for slight sound changes

Sound and RPS…

does sound like pinion to bevel not right.

I couldn’t get the video to work. But a general check can be this.

First. Motor height. High Screamy is generally to high motor height. Low screamy/Grindy is too low.

Experiment a little and you’ll notice the tone change. If it’s still loud or if the motor or grip are getting hot quick your shims are likely too tight. The others have talked to you about the shaft movement.

If you’re still worried. Take out the cylinder and related parts so it’s just the gears j. Close and screw in the gearbox and try to spin the gears. Do they spin freely or require effort and stop quick. That’s an indication they are too tight. If they spin freely check the shafts for lateral movement again and adjust as needed with shims.

Too many shims would cause the gears to not spin easily/freely, which would make the motor work harder, so it and the wiring/battery may get warmer than usual.

Ur GB should/will have some windows. Poke something in somewhere and see how easily they turn (with the spring out)…

I think it isn’t the motor height, because the adjustment scre at the bottom of the grip is as lose as it goes. I think I may have put too many shims on the bottom side of the bevel gear, which would push it into the pinion. This could be related to another problem I had when reassembling which was that the motor would need to be pushed far to one side of the grip to go the whole way in.

… i cant find the link, but bunnings sells a set if mini files made by trojan.

Its gunna sound funny, but they have been invaluable in building gearboxes

There is an oval one with a point, and a flat one

The flat one will help you with the ar latch. You can hold it in place through the motor hole, and the oval one helps you position the gears when closing the box up

The oval one also is perfecy for checking shimming.

In 95% of all boxes, you want 0.05-0.1mm of movement once you close up the box. If there is no movement it’s probably too tight

The only box ive shimmed out 100% of movement and the gears still spun freely was the laylax Prometheus box

I personally start at the spur gear, then the sector, leaving the bevel last.

With the box empty, shim the spur, so its just clear of the box. Start with no shim, and add 0.1 until when you spin it, it spins freely, and doesn’t touch the housing

Close up the box, with a screw at the back, near the trigger, and one near the motor. Tip it upside down, and push the spur gear up with something pointy, that file I mentioned, and check movement. Should be heaps. And shim till there is very little

Next, the sector gear. Add that and you want to shim it until its just clear of the spur. Will be scratchy like the spur until its clear. Close up the box and do the above check.

If you have it right, you should be able to spin the sector and both gear should spin freely, and for a while, without grease. Bearings will spin longer, bushings should still get plenty of rotations

If you dont, something is too tight

Edit - forgot this bit.
Hold it flat and spin. Should be quiet. The. Flip it over and spin it. If its scratchy, shim the sector away from the spur a little more until its quiet both up and flat on both sides

Make notes as to how many shims per side per gear

There are a couple of different ways to shim the bevel

I shim the bevel until its like above but centered in the box. So the same number of 0.1mm shims either side

Take the top of the box, the bevel, and the shims for that side. Attached the pistol grip to the side of the box, add the bevel and shims, and add the motor.

Here you adjust the pinion height until the pinion is as centered on the bevel as you can make it.

If the bevel shifts, its to high, and pull a shim out of that side until it doesn’t shift. Make sure you add those shim to the other side.

If its loose, go the other way, until its not.

Make more notes

To test shimming, put all the gears and shims into the otherwise empty box, and see if you can spin the gears.

They should spin freely, but due to the bevel not like before.

If its too tight, youll struggle to spin the gears

Now you grease. If you try and spin the gears once greased, it wont spin. You have to do it before you add lube. Sounds silly, but …

Then. Build the rest of the blaster.

Dont forget to check the height of the ar latch. If you have had to shim the height of the spur plenty to clear stuff, like i had to with an mk box, your ar will catch, and you will need to shim. This will make the ar latch really hard to keep in place while closing the box. Ive found the $5 ar and the shs ar latches have a short shaft and suck installing.

The lonex latch is nice.

If you get spur and sector right, it should be very quiet.

If its still scratchy, the grip is out of alignment and the pinion is not centered on the bevel properly


Awesome write up m8 the moderators or someone should save that in the begginers biy as that was really informative and yet easy to read… Well done cheers

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Shimming methods vary and everyone has their own method.

I usually shim until there is minimal play in each gear axle. This is confirmed by pushing on the axles from either end with the gearbox closed up. If this can’t be done or the axle does not have enough purchase on the bearing/bushing then that needs to be addressed.

Then I work out whether the shims go above or below each gear starting with the sector gear centred and meshing with the piston ladder.

I figure I can modify the motor/pinion height at the other end whereas the ladder position is what it is. Again, that’s just me.

It’s a relatively quick process. :sunglasses:


The sound of pinion to bevel. Adjust the motor mate check shims. From the video it doesn’t sound right.

Fair few videos on the tube that will be of very good assistance.


Strike 4 :joy:.

Ok I’m officially out tonight. Have a good un chaps :beers::tada:

Edit: comment above.


Peace out brother :sunglasses::+1:

Today I pulled the blaster apart to look at the shims and if the gears are too tight, and I think I’m going to need to reshim the gearbox. When I was testing, I was using a thicc RV car battery, that is a 7.4v lips with 50c discharge rateusing the deans connector. I noticed that the cable that connects the gearbox to the battery connector was very hot, and I was wondering if this is to be expected with bigger batteries?

In my experience, no.

Your wires got hot cos the motor was struggling to turn the gears.


Yeah most likely too tight shimming or motor height so too much draw from motor trying to turn it all

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First shimming video i used to shim my first box. A gen8 - https://youtu.be/m0yU-_prZyY

Was a 2-3 hour exercise

Watch this, (how i shim now) - https://youtu.be/CbJbRpwII_0

Usually done in 5-10mins. Then 30 to put the box back together and test. It’s easier completely empty, without the trigger block, but not 100% necessary

And watch this - https://youtu.be/ECRhjvhkTic

the first one from TheAirsoftTech ive watched before and is quite good.
that second link is a painful watch. dude rambling about crap for the first half.

highly recommend Rattler guide - Shimming for dummys guide - AEG Automatic Electric Gel Blaster / Gearbox & Gearbox internals - Gel Blaster Forum