Screeching Gears

[Red_Dog]

Hi guys, I've bought a UK spec SPR-M (20K motor) and have done some tinkering with it (inner barrel to fix the awful cylinder:barrel ratio, outer barrel/moderator for looks, stronger spring (SP100) to bump power back up).

I've been looking to up the trigger response a little so I've picked up a high torque motor (ASG 22TPA) and the Krytac compatible Prommy gear set (13:1).

I fitted both components and it was awful, screechy, and jammed.

I redid my shimming, removing most of it until I had loose shimming and retried without compression part, still bad. 

here's a list of what I've tried:

- New gears & new motor = screeching,

- new bevel & new motor = screeching, 

- stock gears & new motor = screeching,

- stock bevel & new motor = screeching,

- & stock gears & stock motor = grinding (this was not present before).

I've tried with and with the anti-reversal latch, mixed old bevel with new gears (they fit by the way) and vice versa without any luck.

Any ideas? 

Further context.

I have cleaned and regreased the gearbox. 

Using the half shell method I can see that the pinion gear is riding too high over the bevel, in all 4 configurations, I believe this is my issue, I just don't know why it's happening now.

The body, grip, wiring harness, gearbox shell, etc. are all stock and have not been an issue before.

 

[Iceni]

the pinion gear is riding too high over the bevel, in all 4 configurations

Did you adjust the motor position. There's a screw in the base of the pistol grip that should move the motor in and out.

There can also be issues with pistol grips setting the incorrect engagement angle to the bevel. I don't know that guns pistol grip configuration but sometimes just testing with a different grip can sort a lot of problems when you have gone through so many options without success.

 

[Adolf Hamster]

sounds like the bevel is too low, so you'll need to shim it up to get a better mesh (you may be limited by the requirements of the sector/idler)

this is assuming the motor is positioned ok within the grip, never worked on one but i've heard the krytac stuff is extraordinarily picky when it comes to the motor positioning.

 

[Red_Dog]

Did you adjust the motor position. There's a screw in the base of the pistol grip that should move the motor in and out.

There can also be issues with pistol grips setting the incorrect engagement angle to the bevel. I don't know that guns pistol grip configuration but sometimes just testing with a different grip can sort a lot of problems when you have gone through so many options without success.

It doesn't matter how I adjust the motor height, it's either a jam (too high) or screeching. 

Surely my stock pistol grip, stock gearbox, stock motor, & stock gears should sound the same as they used to though? 

sounds like the bevel is too low, so you'll need to shim it up to get a better mesh (you may be limited by the requirements of the sector/idler)

this is assuming the motor is positioned ok within the grip, never worked on one but i've heard the krytac stuff is extraordinarily picky when it comes to the motor positioning.

Literally the opposite here, I can't get the gear low enough, trying to tailor the motor height with the half shell method resulted in my gears running a bit too close to the shell or forcing my bevel off axis. 

Yeah, the baseplate does basically all of the positioning, though I did try shimming the motor to prevent play and to shift it away from the bevel (separately) but to no avail. 

 

[Skara]

Well I think you have the same issue I'm having on my KA PDW.

On mine the new motor is longer than the stock one and despite having completely removed the motor adjustment screw, it is still way too high and causes mad screeching.

Check if your new motor is longer than the stock one, if so, I'm afraid you'll need a different pistol grip.

 

[Red_Dog]

Well I think you have the same issue I'm having on my KA PDW.

On mine the new motor is longer than the stock one and despite having completely removed the motor adjustment screw, it is still way too high and causes mad screeching.

Check if your new motor is longer than the stock one, if so, I'm afraid you'll need a different pistol grip.

Not for here, the new motor is maybe a mm shorter. 

The pinion profile might be a little different, but I can't tell if it's my eyes playing tricks of me, I've got a pinion puller coming now. 

 

[Misery]

have you checked to see if eaither side of the gearbox case is slightly warped at all?

 

[Iceni]

Surely my stock pistol grip, stock gearbox, stock motor, & stock gears should sound the same as they used to though? 

You would think it would all settle back to normal when you reset everything to stock.

What else did you change with the configuration? Bearings/Bushings? Did you put shims on the high side of the bevel?

Because All I can think is you've dropped the bevel gear too low on the pinion, And that's causing a poor mesh then a friction lockup. If you added shims or didn't seat the bearing/bushings fully, or those bearing/bushings are thicker than the stock ones then this would happen. It's the upper shell you need to inspect.

I've done something similar on v3 gearboxes when following v2 guides. You set everything starting with the sector and think the bevel will just play nice and it doesn't. Then you have to work from pinion first and you find the tappet plate locks up.... There's a balance between those points that your gears need to be in, The sideways mesh gear to gear is largely irrelevant provided 90% of the tooth is in engagement, And you have shimmed out the sideways movement between the shells.

Without actually seeing it it's not an easy diagnosis.

Another thing of note is the pinion puller isn't going to fix anything. You've already swapped pinions with the motors, You've already adjusted the height with the motor screw. Pulling a pinion at this stage is just moving the same problem about and isn't going to fix the issue.... If it is bevel height, then all the pinion puller will do is change how many turns it takes on the motor adjuster to go from screaming to lockup.

 

[Adolf Hamster]

With just the gears and the box tightened up do the gears sound nice when spun by hand?

You can also then fit the motor to be sure the screeching is coming from there.

 

[Sitting Duck]

& stock gears & stock motor = grinding (this was not present before)

well then it is "something" you have done with all the experimentation

(pretty obvious - but if all back to stock & still shit then something has taken place)

Only you know what you have done, likely the shimming/height is not the same as it was

The only other thing I can think of is something else you altered/changed (& not mentioned)

eg: new piston that is ultra fucking tight binding, causing extra drag/load

(way more than a smidge higher spring)

 

[Red_Dog]

have you checked to see if either side of the gearbox case is slightly warped at all?

I have, I can't see anything at all, nor can I see any damage on the bearings. 

well then it is "something" you have done with all the experimentation

(pretty obvious - but if all back to stock & still shit then something has taken place)

Only you know what you have done, likely the shimming/height is not the same as it was

The only other thing I can think of is something else you altered/changed (& not mentioned)

eg: new piston that is ultra fucking tight binding, causing extra drag/load

(way more than a smidge higher spring)

The shimming was returned to original (one brass shim on either side + spring on spur), the gears, spring, motor, & grease are the only gearbox components I have changed (new shims with new gears, but I returned to stock for the stock gears). 

 

[Red_Dog]

You would think it would all settle back to normal when you reset everything to stock.

What else did you change with the configuration? Bearings/Bushings? Did you put shims on the high side of the bevel?

Because All I can think is you've dropped the bevel gear too low on the pinion, And that's causing a poor mesh then a friction lockup. If you added shims or didn't seat the bearing/bushings fully, or those bearing/bushings are thicker than the stock ones then this would happen. It's the upper shell you need to inspect.

I've done something similar on v3 gearboxes when following v2 guides. You set everything starting with the sector and think the bevel will just play nice and it doesn't. Then you have to work from pinion first and you find the tappet plate locks up.... There's a balance between those points that your gears need to be in, The sideways mesh gear to gear is largely irrelevant provided 90% of the tooth is in engagement, And you have shimmed out the sideways movement between the shells.

Without actually seeing it it's not an easy diagnosis.

Another thing of note is the pinion puller isn't going to fix anything. You've already swapped pinions with the motors, You've already adjusted the height with the motor screw. Pulling a pinion at this stage is just moving the same problem about and isn't going to fix the issue.... If it is bevel height, then all the pinion puller will do is change how many turns it takes on the motor adjuster to go from screaming to lockup.

No other changes, unless the outer/inner barrel, hop up bucking, & nub can influence the gearbox (I've played a game with this configuration, so nothing I can see). 

I've tried with & without shimming on both stock & new gears, without a shim the bevels scrape, with a single shim it runs silently, I did shim both sides until there was minimal play. 

I washed the gearbox (stripped it completely, washed in warm, mildly soapy water and cleaned the corners with a toothbrush, rinsed the bearings then dried the halves on a towel next to a radiator, using PC duster gas to ensure there wasn't water in the gearbox), I checked bearing function at every stage without issue. 

If they're out of position I can't see it, they don't shift at all and never have done. 

The thing is pretty subtle and I doubt I can get a good enough photo, but I'll try that when I get a chance, but the bevel gear tipped when the pinion is applied, almost like it's shimmed too high, but this happens without shims. 

I can appreciate that, I bought it before I'd realised that the stock set up was being an issue too. 

I've got some bushings and I might try fitting one below the bevel and slimming it down further, just to see if it'll help. 

 

[Misery]

its your bearings scrreching i bet! water and bearings do not mix even blowing it out with the pc air tins and on a radiator to dry is not a gd idea

 

[Red_Dog]

its your bearings scrreching i bet! water and bearings do not mix even blowing it out with the pc air tins and on a radiator to dry is not a gd idea

They're fully greased again and it was next to a radiator, definitely not on one. 

I'll take a proper look anyway, it's not like I can find anything else here. 

 

[Misery]

yeah id still not put water near em bud just one of those things espicialy the open type like them,

yeah man another thing to rule out so u know for sure

 

[Iceni]

I feel your pain on this one.

Give those bushings a shot, You might have something akin to a collapsed bearing or damaged bearing cage. The fact you are saying the bevel looks to be tipped under load is suspect. Bearings don't always fall apart. The internal cage is there to keep the balls evenly spaced. Without the cage or with damage to the cage you can generate lockups.

I'm at a loss with this whole gearbox TBF. If the bushings don't work I'd be tempted to send the bugger out to a tech.
 

 

[Red_Dog]

I feel your pain on this one.

Give those bushings a shot, You might have something akin to a collapsed bearing or damaged bearing cage. The fact you are saying the bevel looks to be tipped under load is suspect. Bearings don't always fall apart. The internal cage is there to keep the balls evenly spaced. Without the cage or with damage to the cage you can generate lockups.



I'm at a loss with this whole gearbox TBF. If the bushings don't work I'd be tempted to send the bugger out to a tech.
 

The bearings are fine (evenly spaced, I can't induce shifting by twisting or titling them or anything), visually at least, this thing is confounding me. 

I've just opened the gun back up, just to see if I can drop the SHS bushings in, they'll need some modification to slim them down, but they'll fit for sure. 

Basically (it doesn't show well in a photo unfortunately) the 'rim' on the bushings is a lot thicker than the bearings, even though the bushings are a lot thinner over all (~3mm bearing thickness w/ .5mm 'rim' vs ~2.5mm bushing w/ 1mm 'rim'). 

I'm planning on dremeling one of them down to fit, then trying that for a bit, if that doesn't work I'll try and recess the hole in the gearbox by a sliver and pushing the bearing in further to reduce its effect upon the gear. 

yeah id still not put water near em bud just one of those things espicialy the open type like them,

yeah man another thing to rule out so u know for sure

I've gone over them with WD40 so that'll sort any water problems out, I'll regrease them tonight but they're not showing any rust or sticking, so we should be set. 

 

[Shamal]

The bearings are fine (evenly spaced, I can't induce shifting by twisting or titling them or anything), visually at least, this thing is confounding me. 

I've just opened the gun back up, just to see if I can drop the SHS bushings in, they'll need some modification to slim them down, but they'll fit for sure. 

Basically (it doesn't show well in a photo unfortunately) the 'rim' on the bushings is a lot thicker than the bearings, even though the bushings are a lot thinner over all (~3mm bearing thickness w/ .5mm 'rim' vs ~2.5mm bushing w/ 1mm 'rim'). 

I'm planning on dremeling one of them down to fit, then trying that for a bit, if that doesn't work I'll try and recess the hole in the gearbox by a sliver and pushing the bearing in further to reduce its effect upon the gear. 

I've gone over them with WD40 so that'll sort any water problems out, I'll regrease them tonight but they're not showing any rust or sticking, so we should be set. 

You shouldn't really use wd40 on guns as it is hygroscopic and will attract moisture and promote rust.

Regards 

 

[Misery]

yup wd40 isnt gd for it either

 

[Red_Dog]

Well I've run out of ideas, nothing I can do is working so does anyone know a good tech in the Southwest (I'm in Bath)?