Version 3 Gearbox lockup & Piston Damage - ICS AK74M

[Northman]

Hello Everyone,

I am after a little assistance with my version 3 gearbox as I'm pretty new to working on my own kit but I'm keen to learn, rather than just send it into the tech shop everytime I have an issue.  I'll give you a brief run through of the issues I've had with my AK and what I've done to date;

Initial Problem - FPS - I purchased the rifle second hand and it was in good condition as the previous owner had hardly used it, I took it apart and this confirmed everything was in a good condition however at my first skirmish it was chrono'd at 220 which dropped to 160-180 at the next skirmish.

Initial Solution - Replacement Piston Head & New Spring - I did a compression test which highlighted excessive leakage so I ordered a new piston head which seemed to provide better results as well as a new spring for good measure.  This resulted in a consistent 340 FPS which was exactly where I wanted to be - Great! I thought and was feeling pretty good as I'd actually fixed something!  That lasted until I took it to a skirmish this weekend...

Current Problem - Seized & Piston teeth wear - It lasted one game before gradually getting slower and slower until it completely stopped firing - almost as if the battery was dying - which I thought was the case until I swapped it over and nothing.  Luckily I could borrow an AEG so it didnt spoil my day but it was frustrating.  I've now had time to take the gearbox apart and I found the spring was fully compressed in the cocked position and after closer inspection, there is no damage apart from wear to the first 3 teeth on the piston which was there before, and some new minor wear along the length of the piston teeth which is more prominent towards the end of the piston - image below. 

View attachment 30401

Current Solution - Well that's why I'm here...

The guns an ICS and has to be downgraded to be within UK limits so I know it can take an M100 spring and other than the piston no other parts have damage.  It was suggested by some people at the skirmish on Saturday that I maybe need to use a stronger battery (I currently run a 9.6V battery but looking to lipo up soon) but the new damage to the piston suggests there's another problem, and I think any increase in power would result in further damage.  

I'm buying a new piston regardless but just wanted to ask more experienced tech's what their opinion is?  

Thanks in advance!

 

[Hangtight]

Put just the piston in the gearbox and no up the screws. Is the piston free to move back and forth on the rails under its own weight?

 

[Northman]

Put just the piston in the gearbox and no up the screws. Is the piston free to move back and forth on the rails under its own weight?

Click to shrink...

Thanks for the quick response and yes it moves under its own weight. 

 

[Hangtight]

And how tight is the piston head with O ring in the cylinder? It should be easy to move.

What lubrication did you use when you reassembled it?

Sorry for all the questions, just trying to eliminate things one by one!

 

[Northman]

And how tight is the piston head with O ring in the cylinder? It should be easy to move.

What lubrication did you use when you reassembled it?

Sorry for all the questions, just trying to eliminate things one by one!

Click to shrink...

Yes, it's easy to move - initially, I thought it should be tighter but I searched and watched some vids and sound it is as it should be.  

Ask away - I really appreciate your help!  

EDIT - Lubricant I used was the silicon grease that's in the Nurpol kit

http://www.patrolbase.co.uk/airsoft/1-nuprol-airsoft-maintenance-kit.htm#.WlvLo0ycZPM

 

[madmogga]

Firstly 9.6V is more than enough battery as you said you changed I doubt that’s your problem.  I am no expert but looking at the piston that’s a lot of wear for just one game, so worth checking how the teeth on the gears mesh with the piston, I have in the past seen that using parts from different manufactures do not always mesh correctly. Also is your ics a split gear box ? have you looked to see if you have any muck in the lower gear box that the gears might be picking up ?

Another thing to consider is the piston wear and the gun getting slower might be two separate issues, as an example your wiring / motor might be defective or even a slight shorting out leading to a rapid drain in the battery ? when you changed the battery was it 100% fully charged ?

 

[Northman]

Firstly 9.6V is more than enough battery as you said you changed I doubt that’s your problem.  I am no expert but looking at the piston that’s a lot of wear for just one game, so worth checking how the teeth on the gears mesh with the piston, I have in the past seen that using parts from different manufactures do not always mesh correctly. Also is your ics a split gear box ? have you looked to see if you have any muck in the lower gear box that the gears might be picking up ?

Another thing to consider is the piston wear and the gun getting slower might be two separate issues, as an example your wiring / motor might be defective or even a slight shorting out leading to a rapid drain in the battery ? when you changed the battery was it 100% fully charged ?

Click to shrink...

Hello! Thank for the response!  

I checked how the teeth mesh with the gears before and it seemed ok, but I will check again tonight and make sure it's as it should be.  

Also, the Gearbox is completely standard (not a split gearbox) and I've only swapped parts (Pistonhead, Spring) rather than upgrade at this stage.  Its immaculate inside as I did a full service and there is no wear on any other parts.  The only bit of debris I found was a small shaving of plastic which appears to have come off the piston teeth, which could have jammed the gears but is not the underlying problem.

The wiring is an interesting point as there's very little slack in it currently which makes getting the wiring into its cavity and the gearbox in the receiver, quite time-consuming and maybe I have damaged it in the process?   

The battery was fully charged but I borrowed another from my cousin just to be sure and I had the same problem. 

 

[RR01]

You mentioned that you changed the piston head.  Did you check the AOE (angle of engagement) of the piston with the sector gear before you put it all back together?  It looks like the teeth on the sector gear are not picking up the teeth on the piston correctly, which is why you have wear.  It may also be that when it locked up the teeth on both the gear and the piston were jammed together, stopping it from rotating to the point where the piston is released. Have a look here: https://www.patrolbase.co.uk/blog/angle-of-engagement/.

 Also try Googling for other videos and instructions it that isn't clear.

 

[madmogga]

just another thought and things to look at if you have had the gearbox apart - have you checked the shimming is not to tight - i.e. if you screw closed the gearbox without the motor and piston in place do they spin freely, also motor height if its in to far that would slow everything down a lot, although you will hear it scream like made   

 

[Northman]

You mentioned that you changed the piston head.  Did you check the AOE (angle of engagement) of the piston with the sector gear before you put it all back together?  It looks like the teeth on the sector gear are not picking up the teeth on the piston correctly, which is why you have wear.  It may also be that when it locked up the teeth on both the gear and the piston were jammed together, stopping it from rotating to the point where the piston is released. Have a look here: https://www.patrolbase.co.uk/blog/angle-of-engagement/.

 Also try Googling for other videos and instructions it that isn't clear.

Click to shrink...

I must admit I followed a youtube video for a V3 disassembly and can't remember the guy doing any work on AOE.  And from trawling the internet for damage caused by bad AOE it seems to be consistent with what's happened.  I'm going to check when I get in tonight and maybe buy a SORBO pad if required and obviously a new piston with reinforced teeth. 

just another thought and things to look at if you have had the gearbox apart - have you checked the shimming is not to tight - i.e. if you screw closed the gearbox without the motor and piston in place do they spin freely, also motor height if its in to far that would slow everything down a lot, although you will hear it scream like made   

Click to shrink...

I am still using the shims that were in it from before thinking that it should be fine!  I will do this test also tonight and add a pack of new shims to the order if required. 

I'll let you know how I get on but thanks for the help guys!  

 

[Northman]

I must admit I followed a youtube video for a V3 disassembly and can't remember the guy doing any work on AOE.  And from trawling the internet for damage caused by bad AOE it seems to be consistent with what's happened.  I'm going to check when I get in tonight and maybe buy a SORBO pad if required and obviously a new piston with reinforced teeth. 

I am still using the shims that were in it from before thinking that it should be fine!  I will do this test also tonight and add a pack of new shims to the order if required. 

I'll let you know how I get on but thanks for the help guys!  

Click to shrink...

Further to my last post I've looked into the AOE and it doesn't look too great, here are the results! 

 View attachment 30488

I've done a bit of reading into it and the teeth need to be as flat as possible against each other to distribute the load and minimise wear on other components, so I'm going to get a spacer (sorbo) to hopefully rectify the problem.  I'm also going to get a new piston with steel teeth, piston head upgrade and a new cylinder.  

Gears turn fine so there doesn't appear to be a need to re-shim though I will remember the test for the future! 

I'll let you know how I get on!  

 

[Northman]

Further to my last post I've looked into the AOE and it doesn't look too great, here are the results! 

 View attachment 30488

I've done a bit of reading into it and the teeth need to be as flat as possible against each other to distribute the load and minimise wear on other components, so I'm going to get a spacer (sorbo) to hopefully rectify the problem.  I'm also going to get a new piston with steel teeth, piston head upgrade and a new cylinder.  

Gears turn fine so there doesn't appear to be a need to re-shim though I will remember the test for the future! 

I'll let you know how I get on!  

Click to shrink...

Hey I'm back with new parts and new problems!   So I spent some money on new parts below;

ASG V3 Ultimate Cylinder Head

ASG Ultimate Cylinder

MAD BULL Blase Orange Polymer Piston - Full metal teeth rack

Shim set

ASH V3 Ultimate Tappet plate

A new bearing spring guide

SORBO pad from AirLabs

This has enabled me to fix AOE as well as well as upgrade certain parts that were worn as well as reshim the gears.  The problem is once I've put it all back together I test fire it and get either nothing or only about 2-3 shots off before it locks with the spring fully compressed.  Maybe I've over shimmed it? 

Ugh I'm drawing a line tonight and will have another crack tomorrow but just wanted to drop an update in here.

 

[Hangtight]

Did you remove any material from the piston teeth when you installed the sorbo pad?

 

[madmogga]

from what i can see the MAD BULL Blase Orange Polymer Piston - Full metal teeth rack has the second tooth removed so should be ok so unless your AOE was way out i doubt you need to touch the third tooth .

When you shimmed the gear box did you test it screwed down without motor and piston to ensure they run free - also did you do it by shimming the bevel gear and motor first ?

are you able to post a video if i can  see / hear it what your guns doing might help me pin point the issue a bit better 

 

[Northman]

Did you remove any material from the piston teeth when you installed the sorbo pad?

Click to shrink...

Hi!  I got a completely new piston with full metal teeth rack and it also has number 2-3 removed and was sure to clean the gearbox of debris beforehand, I found a small piece of plastic from the piston in the gear teeth! 

from what i can see the MAD BULL Blase Orange Polymer Piston - Full metal teeth rack has the second tooth removed so should be ok so unless your AOE was way out i doubt you need to touch the third tooth .

When you shimmed the gear box did you test it screwed down without motor and piston to ensure they run free - also did you do it by shimming the bevel gear and motor first ?

are you able to post a video if i can  see / hear it what your guns doing might help me pin point the issue a bit better 

Click to shrink...

Yes that's part of the reason I went for it as it saved me the job of grinding down 2 and 3.  The AOE was way out though so I had to install the SORBO which makes both teeth flush or as they should be. 

On Reshimming I followed a guide and started on the bevel gear and worked my way up, checking and reducing lateral/vertical movement - but - not by too much.  However, the gears were not spinning as freely as they were in the demo video though so I may need to start over from scratch. 

One thing I have just remembered (I was tired last night!) is that there was a small gap at the cylinder end between both parts of the gearbox - it just wouldn't close completely shut for some reason - but I'm only talking a fraction of a millimetre. 

I'll get a video up tonight as well as some pictures as like I said it just grinds to a halt in the fully cocked position. 

Again thanks for you help guys! 

 

[Iceni]

It's a V3, could well be the tappet plate.

If the sector gear is shimmed high, so there are fewer shims on the top of the gear, then it'll pinch the tappet plate between the top shell and the sector gear.

This can lock a box. The tappet plate should be free to move and return without resistance. And this needs to be true for all positions of the sector gear. If the sector gear has any blemishes and dings on the outer race then it can grab.

When I shim my v3 I have to work with that space in mind. And it often means the sector gear runs off centre a little on the piston body (running low in the box). And I have to accommodate that by running the rest of the gears slightly off perfect. Fortunately the v3 box can cope with this and there is enough movement to be able to get a decent mesh on the pinion even if you need to move the gears slightly.

 

One thing I have just remembered (I was tired last night!) is that there was a small gap at the cylinder end between both parts of the gearbox - it just wouldn't close completely shut for some reason - but I'm only talking a fraction of a millimetre. 

Click to shrink...

This could also be caused by the tappet plate/sector gear shimming.

I'd go back to the gearbox and start from scratch.

Start with the sector gear by itself. Get the shimming perfect, then drop in the tappet plate and work out exactly how many shims need to be up top for it to run free. Write that down.

Then start the regular shimming process from the bevel gear through to the spur gear. Shim the sector gear like normal to the spur gear, but make a note of how many shims are in what position on the sector gear.

You need to do this because I can guarantee the shimming done properly has put too few shims on the top of the sector gear. Do the math and work out how many shims need to move on the other 2 gears to be perfect on the sector with the best tappet plate gap.

Make the shimming adjustments then check the motor, You should find it'll engage just fine, but it has to be wound in another half turn.

 

[Northman]

from what i can see the MAD BULL Blase Orange Polymer Piston - Full metal teeth rack has the second tooth removed so should be ok so unless your AOE was way out i doubt you need to touch the third tooth .

When you shimmed the gear box did you test it screwed down without motor and piston to ensure they run free - also did you do it by shimming the bevel gear and motor first ?

are you able to post a video if i can  see / hear it what your guns doing might help me pin point the issue a bit better 

Click to shrink...

Ok I've started again from scratch and the results are as per the video below... 

WARNING May make you cringe...

 

[Hangtight]

The motor pinion is way too tight to the bevel... Poor thing!

 

[Northman]

The motor pinion is way too tight to the bevel... Poor thing!

Click to shrink...

I've re-adjusted it and it still wouldn't cycle and I think the motors f*cked now ...I've put some images below because I may just be missing something obvious. 

View attachment 30621

I was thinking that the angle on the new tappet place below needs to be smoothed so the sector gear can rotate better, as it is effectively hitting a right angle once it cycles...so could be forcing the tappet plate against the gearbox.  Thoughts?

View attachment 30622

Another theory I have is that before the whole thing died I had replaced the spring to get the 340 fps as I mentioned in my first post, but now I have added the sorbo to adjust the AOE will I need to clip the spring as it might be getting fully compressed.  Again any thoughts on this? 

It's a V3, could well be the tappet plate.

If the sector gear is shimmed high, so there are fewer shims on the top of the gear, then it'll pinch the tappet plate between the top shell and the sector gear.

This can lock a box. The tappet plate should be free to move and return without resistance. And this needs to be true for all positions of the sector gear. If the sector gear has any blemishes and dings on the outer race then it can grab.

When I shim my v3 I have to work with that space in mind. And it often means the sector gear runs off centre a little on the piston body (running low in the box). And I have to accommodate that by running the rest of the gears slightly off perfect. Fortunately the v3 box can cope with this and there is enough movement to be able to get a decent mesh on the pinion even if you need to move the gears slightly.

 

This could also be caused by the tappet plate/sector gear shimming.

I'd go back to the gearbox and start from scratch.

Start with the sector gear by itself. Get the shimming perfect, then drop in the tappet plate and work out exactly how many shims need to be up top for it to run free. Write that down.

Then start the regular shimming process from the bevel gear through to the spur gear. Shim the sector gear like normal to the spur gear, but make a note of how many shims are in what position on the sector gear.

You need to do this because I can guarantee the shimming done properly has put too few shims on the top of the sector gear. Do the math and work out how many shims need to move on the other 2 gears to be perfect on the sector with the best tappet plate gap.

Make the shimming adjustments then check the motor, You should find it'll engage just fine, but it has to be wound in another half turn.

Click to shrink...

I've reshimmed as you've suggested but still had the problem in the video above and I've adjusted the motor height and still had the same problems - may have knackered the motor now too... ops! 

 

[Iceni]

You might have an electrical fault.

I can't see anything wrong with that build. I thought for a moment you might have a tooth too many on the sector gear but that was me thinking the standard number of teeth was 15 not 16.

Electrical faults can be a bit frustrating with the V3.

You have the dolly that travels in the switch and a lot of problems can be caused by it.

I'd start with trying to bridge the trigger cables to make sure it is or isn't a switch fault. If you can get it to run by bridging the connection points then you know it's either going to be the dolly failing to return and seat correctly, or the connection points themselves are too widely spaced.

The motor is easy to test as well. Just ask your airsofting mates if anyone has an old short shaft motor you can borrow for a couple of days. It takes minutes to swap and test with V3.

Other than that I really can't see anything wrong with the box. If the electricals don't answer the problem then it would probably be best to look for a local tech, to solve it for you.