ARP 9 shimming school boy error

[Wegalaxy]

Hello everyone,

 

When I opened my ARP 9 V2 gear box for the first time, I forgot to keep track of what shim goes where and on what bushing as I generally thought they were all the same size.

 

Since opening the gear box I have lost a shim so I am only down to 4 when from the factory it comes with 5. On either side of the sector gear, also one on either side of the spur gear. And finally one on one side of the bevel gear. 

 

I know this question is a long shot but does anyone know what sizes of shims G&G uses from the factory on their ARP 9s and what size goes where?

 

As I have ordered a pack of different size shims.

 

(I have not adjusted the motor height from the factory)

 

Many thanks

[Colin Allen]

Every gearbox is different; the idea is to shim the gears so that they do not rub against each other and run freely and quietly with minimal lateral movement and the lowest possible load on the battery.

 

Regard this as learning opportunity.

[Wegalaxy]

thank you @Colin Allenlooks like I am watching a how to video. haha

[Adolf Hamster]

@Colin Allen is right on the money here. The reason for shims is because even manufacturers cant rely on the gearbox casing being an exact size.

 

It's very much the case that the number and position of shims in your gearbox is going to be very nearly unique to that specific gun.

 

With that said, as much as we strive for "perfect" shimming, you can get away with a little slop.

 

There are multiple ways to go about it, but this should get you somewhere, for reference "low" means close to the left hand gearbox casing and you should be starting this on a clean casing with everything but the bearings removed:

 

1. Start with the idler gear, keeping it as low as possible add shims under until it isnt scraping on the casing, you can test this by putting the 2 halves together and using a screwdriver to spin the gear whilst holding it left side down.

 

2. Once you've got the underside of the idler figured out, add to the top side. This means closing up the 2 halves and tightening them down (tightening is important) and seeing if it'll still spin. You want the number of shims required to make it stick minus the smallest shim size you're working with (eg if you're using 0.3mm shims and 3 of them makes it stick, use 2)

 

3. Keeping the idler in place now we do the same for the sector gear, starting with the underside keeping it as low as it can be without scraping the casing, cutoff lever or idler gear.

 

4. Now we do the top side of the sector gear, same process as step 2. When spin testing try holding it both ways up incase it scrapes when held to one side or the other.

 

5. Now it's the bevel gear, lot of folks like starting at the bevel but doing things this way we now know how low the bevel is allowed to go before the other gears start giving issues. So we repeat step 1 for the bevel adding shims under until its as low as can be to prevent scraping.

 

6. Now shim the top of the bevel same as steps 2/5

 

7. Now for the laborious bit, you gotta assemble enough of the gun to get the motor meshed with the bevel and driving, which for a v2 style is assembling most of the box but leaving the whole piston/cylinder/spring assembly and the cutoff lever out but keeping the trigger components in, fit the grip+motor assembly and enough of the wiring to let you "fire" it (just full auto is fine, we only need to spin the gears and listen to them).

 

8. Once the thing can be "fired" tighten the motor adjustment screw in until it's pretty tight then fire a short blast (no more than half a second, if it don't spin then holding the trigger down is only gonna heat up the motor/wires and it should spin immediately). If it doesnt spin then loosen the screw a bit and try again until it spins, it will almost certainly sound godawful. Keep backing the motor height out until it's the least godawful sounding it can be.

 

9. Now you gotta take it all back apart again, move a shim from above the bevel to under it and repeat steps 7-9 until you've got the cleanest sound you can. yes this will take a few tried, yes it's a pain in the ass doing all that work each attempt but such is the teching life.

 

10. Now you know where the bevel wants to be for the motor height, take a look and make sure that there's a decent tooth overlap, ie that the small ring of teeth that drive the idler gear are mostly in line with each other, if they arent you might need to go back and lift the idler/sector gear together to get more overlap.

 

Personally, i've always perferred working with 1 shim thickness as it's easier keeping track of a stack of 9 0.1mm shims than trying to remember "thats a .5, .3 and 2 .1's" etc but that doesnt mean having different sizes wont work as long as you keep track of things.

 

It's not a difficult process, just repetitive, annoying, and needs meticulous care to ensure you don't lose track of what shims need to go where.

[Skara]

15 hours ago, Adolf Hamster said:

Personally, i've always perferred working with 1 shim thickness as it's easier keeping track of a stack of 9 0.1mm shims than trying to remember "thats a .5, .3 and 2 .1's" etc but that doesnt mean having different sizes wont work as long as you keep track of things.

I have 0.1, 0.15, 0.2, 0.3 and 0.5 mm shims, less wasted thinner ones to achieve the desired result.

 

 

On a side note, 0.5mm doesn't always equal 0.2+0.2+0.1 or 0.3+0.2 or 5x0.1.

Most likely the stack will be quite a bit thicker than a single 0.5 due to tolerances so there is that too to consider when shimming.

[Wegalaxy]

@Colin Allen @Skara @Adolf Hamster

 

Hello,

 

So I have shimmed my gear box and its OK. 

But sods law has occurred.

The missing shim has emerged .

I now have all 5 factory shims it came with.

Every gear had a shim on it both sides when I opened it up apart from the bevel gear which does not have a shim on the top side. (if the gear box shell was laying with its left side down.)

 

So this brings me to my last question if anyone would have the slightest clue.

Here are all the measurements of the factory shims.

0.1,0.25,0.45,0.45,0.45 

There is a pattern occurring here where the width is kind of dipping.

 

Would anyone recommend the way I should lay these out?

 

No worries if not.

 

many thanks 

 

Edited December 28, 2024 by Wegalaxy

[Skara]

Just now, Wegalaxy said:

Would anyone recommend the way I should lay these out?

Unfortunately without having the gearbox at hand it's impossible.

Every gun wants its own setup.

 

Adolf's guide is pretty good, you can also watch a couple of videos from YouTube (Paragon Armory one being particularly detailed).

Being just 5 shims you luckily only have a "reduced" amount of possible combinations.

Follow the guides and find the combination with the least drag between gears while still allowing free spin.

[Rogerborg]

I'd just forget the factory shimming, and don't start looking for patterns that aren't there. You don't know whether the factory shimming was decent or not: the "indentured servant apprentice" labourer that fitted them might have been at the start or end of their 16 hour shift.  Just start from scratch and shim based on the reality that you encounter.  You'll generally want at least one shim on each side of each gear, even a 0.1mm, just to give the gear something smooth and lubed on which to rotate, but even that's mostly for ritual purposes.

 

 

 

[Colin Allen]

23 minutes ago, Wegalaxy said:

@Colin Allen @Skara @Adolf Hamster

 

Hello,

 

So I have shimmed my gear box and its OK. 

But sods law has occurred.

The missing shim has emerged .

I now have all 5 factory shims it came with.

Every gear had a shim on it both sides when I opened it up apart from the bevel gear which does not have a shim on the top side. (if the gear box shell was laying with its left side down.)

 

So this brings me to my last question if anyone would have the slightest clue.

Here are all the measurements of the factory shims.

0.1,0.25,0.45,0.45,0.45 

There is a pattern occurring here where the width is kind of dipping.

 

Would anyone recommend the way I should lay these out?

 

No worries if not.

 

many thanks 

 

As I wrote earlier; "Every gearbox is different."  Follow the Hamster's guide and learn to shim as a bonus.

[Wegalaxy]

thanks guys I just wanted a quick opinion on that one. i will go with what i found by doing it my way.

This concludes this topic.

Thanks