Motor height adjustment: the free upgrade everyone forgets
motor height adjustment is the one upgrade that costs nothing, takes ten minutes, and makes your AEG noticeably better and more reliable. and almost nobody does it.
i've had replicas straight out of the box that were eating their bevel gear from shot one because the factory just ran the screw in at random. so check this, even on a new replica.
what motor height actually is
your motor sits in the pistol grip. on top of the motor shaft is a small gear: the pinion gear. that meshes with the bevel gear, the first gear in your gearbox.
at the bottom of the grip is a grip plate with a screw in the middle. that screw pushes the motor up or lets it drop. with it you set how deep the pinion meshes into the bevel.
that's all. one screw.
what goes wrong at the wrong height
too shallow (motor too low). the teeth barely touch. under load they skip. you hear a rattling, skipping sound. the teeth of both gears wear down at the tips, and then the problem gets worse. eventually nothing meshes anymore.
too deep (motor too high). the tooth tips of the pinion press against the bottom of the bevel's tooth gaps. enormous friction, a lot of heat, and the pinion literally eats itself into the bevel gear. you hear a high whine or grind. your motor gets hot, your battery drains faster, and you lose power.
both situations end with a new gear set. a decent gear set costs 25 to 60 euro plus re-shimming. for a screw you could have turned a quarter turn for free.
side effect: a motor set too deep draws more current, and that means more load on your trigger contacts and more heat in your wiring.
the method: adjusting by ear
there's no measuring tool for this, so you do it by sound. sounds imprecise, works fine in practice.
what you need:
- an allen key or screwdriver that fits the motor height screw (look at the bottom of your grip)
- a charged battery
- your ears
safety first: magazine out, hop-up open, and point the replica in a safe direction. you're going to shoot.
step by step
1. back the screw all the way out (counterclockwise), until the motor sits as low as possible. not so far that the grip plate falls off.
2. battery in, and pull the trigger. what you hear now is a rattling, skipping, irregular sound. the pinion isn't grabbing the bevel. this is your starting point.
if it already sounds normal here, your motor is already too deep at this setting and you have a replica with something else going on.
3. run the screw in a small amount. a quarter turn, no more. test again.
4. repeat. test every quarter turn. at some point the skipping sound goes away and it just sounds like a normal AEG: an even, slightly buzzing cycle.
5. from that point turn about an eighth to a quarter turn further. this gives some margin, because the motor can drop a little under load.
6. now find the other side. keep turning in quarter turns until you hear the sound go higher: a shrill whine or grind. that's too deep. note where that starts.
7. set it back. your optimum lies between the point where the skipping stops and the point where the whine begins, and then closer to the first. if the skipping stopped at "point A" and the whine started at "point B", sit somewhere around a third of the way from A.
8. test with a full magazine and a few bursts. does it sound even? does the motor grip stay cool after thirty shots?
how good sounds
let me put it in words, because it's tricky:
- too low: rrrrrat-rat-rrrrat. irregular, sounds like something's skipping. because it is
- good: an even, slightly buzzing cycle. you clearly hear each shot, and it sounds the same on every shot
- too high: a high whining or screaming sound over the cycle. often there's more resistance and it cycles slower
if you're in doubt between two settings, pick the lower of the two that doesn't skip. slightly too shallow is less damaging than too deep, because the friction when too deep eats your gears much faster.
the heat test
after adjusting: fire thirty to fifty shots in a row (semi is fine), then feel the pistol grip and the motor.
- hand warm: good
- clearly hot: set too deep, or your motor is overloaded by a strong spring
- cold but it skips: too shallow
when to re-adjust
- after replacing the motor
- after opening the gearbox
- after replacing the gears or re-shimming
- when you start playing a new replica (including a new one out of the box)
- if your sound changes. this is a good reason to listen briefly after every game day
common mistakes
running the screw in as far as possible "so it sits tight". this is the most common mistake and it's exactly wrong. you eat your bevel gear.
adjusting with a half-empty battery. the motor turns slower then and the sound is different. use a full battery.
only listening to the shooting with an empty magazine. under load (with a BB in the chamber) it sounds different. test both.
thinking this improves your hop-up or accuracy. it doesn't. this is about reliability, trigger response and lifespan.
keep turning while it's skipping. every second of skipping grinds tooth tips off. test briefly, a few shots at a time.
bonus: what else belongs with this
motor height is one of three things that together decide whether your gearbox lasts. the other two:
- shimming. making sure your three gears run in line without play and without binding
- AOE (angle of engagement). making sure the sector gear engages your piston tooth at the right angle
motor height you can do without opening the gearbox. the other two you can't. if you have the gearbox open once, do all three. i've written a detailed workshop guide on it.
if you only do one thing: the screw. ten minutes. costs nothing.
Also on Airsoft-FOB
- also available in dutch: Motorhoogte afstellen: de gratis upgrade die iedereen vergeet