Very specific shimming issue

[dave38x]

Evening ladies and gents,

I have a bit of a shimming issue. My AR is well shimmed - there is no play between the gears and the gearbox shell, they mesh as best they can and they run very very smoothly. For reference I am running SHS 16:1s and an SHS High Torque motor

My bevel gear is shimmed as low as it will go in the gearbox shell without colliding with the gearbox walls, and yet I cannot get my motor to run quietly in the bevel gear (lowering the gear as far as it is and increasing the motor depth has made it a lot quieter). The pistol grip/gearbox alignment also seems to be pretty damn good.

The gearbox shell is a G&P 8mm shell, one of the reinforced ones with lots of excess metal everywhere. I know that my shimming technique is not the issue as I've built 5 or 6 gearboxes using exactly these gears/motors and got them all dead silent, both in V2 and V3 gearboxes.

Has anyone (SniperJesus if you happen to read this in particular) got any advice? I'm considering dremmelling some material out of the gearbox where the bevel gear sits in an attempt to get it to sit a bit lower, but I'm hesitant in case I write off the GB shell. I've a feeling that trying to thin down the back of the pinion gear is a very bad idea from a stress perspective.

[sj_asc]

Re: Very specific shimming issue

Sorry for the late reply,
The issues are likely to lie with the motor/pinions position rather than the gearbox shell it's self.
If you have exhausted all other methods of gear height adjustment (i.e; checking that the bearing including flange seat flush with the shell, pinion height limitations etc..) then it may be worth looking to the motor and it's position, mainly the bearing tower and it's outer diameter compared to that of the shells guide shaft.

Some V2 Guide shafts can be as wide as 10mm, and long type towers smaller than 9mm, that could mean as much as a full mm of play in which the motor/pinion gear alignment can vary, this could then incorrectly be affected/determined by the pistol grips guide hole width and or the alignment with the GB shaft, Wiring or the grips end cap.
With such play, even if correctly aligned, the tower/pinion would not be properly secured and the outward bias of the spinning gear would always throw it off centre.

There will always be a bit of play, but slightly too much as said could put the pinion out of gear shimming range. What may be required is a small collar for the existing shaft or a thicker tower.

The difference in brands often causes headaches as rather than stick to Marui spec, often come up with their own wild dimensions, and SHS along with a few other budget brands have had questionable QC in the recent past.

Sure there are probably wider pinion heads and lower seating bevels out there, they may run a little quieter than the existing gear, but if the guide is off spec and insecure it will unearth its self sooner rather than later, especially at speed! always better to rule it out first



Failing this, other possibilities (sorry if some sound a bit simple!)

* kind of covered above, but off spec motor bearing tower

*lemon pinion gear?,

*off spec seating for gear bearings - shell defect (unlikely),

*incorrect or a dud bevel.

* Failed bearings (g&p 8mm's aren't shielded, check that they are all intact),

* Motor adjustment range - with the grip screw fully loosened ideally the pinion shouldn't be meshing at all. Also is the tower spring correct?


*With the grip cap removed, motor should be able to be pressed in and spring back positively.

[Jez Armstrong]

Re: Very specific shimming issue

Can I ask what pistol grip you are using? I found that cheap magpul ones put the motor at a slight angle causing misalignment and noise

Sent from the toilet whilst having a dump

[dave38x]

Re: Very specific shimming issue

Jez: King arms g27 on a dytac body (same spec as G&p)

Sniperjesus - that's definitely given me a few things to look at I've got a couple of spare pinions, mine is showing a fair amount of wear so that's probably the first thing I'll check. Thanks very much matey!

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