Advice please on short stroking and premature engagement

[Sitting Duck]

Ahhh - see that is what I said about new spring = new piece of paper....

OK you are at 348-350, adjust the hop a smidge and it should drop a little

Also if you set the hop a smidge further for say 0.25's then when chrono'd on 0.20's you will be ok

This is not cheating the chrono as you are using 0.20's to chrono on a hop set for 0.25's

So unless the bb's are going mega sky high straight away it will pass the chrono

very few places will demand the hop set to zero or we would all be 15fps over the limit

Right the shimming is out of whack then when you changed to 16:1 gears perhaps ???

No way should a 16:1 gears & 40k motor setup be shooting that slowly - no bloody way

On a v3 it is a tad easier to check & set the bevel height to pinion

place bevel in top half of box fit the motor cage up and check it meshes back on just right.....

see this long post about shimming stuff....





Odd thing is the bevels for the SHS 13 & 16 sets "should" be the same so it "should" be still correct unless you swapped stuff

Even so you should check the height and such......

Then gauge what shims required on top of bevel - forget under the bevel

the pinion will keep the bevel in place so it won't drop down

the bevel is the only gear you don't have to shim most of the slack out of it

just get the height of motor and height of bevel - determined by shims on top - get these correct

if there is a load of slack underneath afterwards no biggy - take up the worst of this but a bit more slack is fine

(the pinion holds the sod in place like I said)

Space out the other two - usually sector is often shimmed half & half say 0.20mm  on each side

(but you got bearings so this rough amount might be 0.35mm on each side

Spur is usually shimmed about 0.20mm under neath and what is needed on top

THIS CRAP IS A ROUGH ROUGH ROUGH GUIDE ONLY !!!!!!!

Every box is different, SHS gears are quite chunky and bushings needs much less shimming than bearings

So do not take any of this as gospel - you need to check all the stuff yourself

But the motor height must be set, then bevel shimmed to the pinion

Something is well skewed on the shimming most likely to be losing rof like that

Honestly that f*cking motor & bevel crap is so damn critical to how the box runs....

But the bevels for both sets of SHS's should be the same I would of thought ???

should be the same bloody bevel gear I think so I don't how it has all gone tits up

The gun must have been going nutz at 25+ rps originally and double firing with AB turned off

I mean std guns will shoot about 12rps

deans + rewire + mosfet would boost by about 15% so that equates to say 13.8 rps or 14 rps

16:1 gears will improve about 8% to get to 15 rps on $hit stock motor say 20k

then use a 30k motor so we go a third faster again = 20 rps

or 40k motor gets up near 25rps on 16:1 or 30+ on 13:1 gears

So that is where the speed figures come from along with previous rough builds done right

Now all guns will vary but your spring is a faded one on a long barrel hitting 348fps

this would most likely be a 320fps medium length build gun or sub 300 mp5k using same spring

So that spring isn't insanely too strong, so you should be hitting those figures in my mind

So that rof is well down imho - check the shimming thoroughly coz that is where you are being robbed

 

[Sitting Duck]

Daft question.....

You mag is feeding 101% ???

same mag, same nozzle & stuff

not being funny but gears are not shimmed right or bb's are misfeeding a bit to see the rps drop like that

eg: 1-1-1-0-1-1-1-0-1-1-1-0-1-1-1-0-1-1-1 etc... to see the rof drop out of the ordinary ???

something ain't quite adding up to me

did the 13:1 set have a delay clip or something to assist feeding

has nozzle changed - large nozzle that doesn't clear to chamber bb

worn out tappet fin not retracting the nozzle back far enough to feed properly again

using a different mag with a weak spring not wound enough high cap

if mid cap - don't be fooled they always feed better than high caps

(had a couple of mid cap M4's that bb's were snagging in the bends on the mag/spring and thus stopped feeding 101% at times)

Jeez that was a nightmare - stripped the gun twice more before I realised it was the f*cking mid cap I was using

jeez the air was dark navy blue that day

 

[madmogga]

I think it was feeding ok but I'll check that first as I did change the nozzle but from what you have said I think it's my shimming it's only my second attempt and although the gears mesh ok and spin free with the gear box closed I must admit I did not even shim for or check the motor height dammit I knew I would miss something 

 

[Sitting Duck]

I think it was feeding ok but I'll check that first as I did change the nozzle.....

Click to shrink...

STOP CHANGING STUFF !!!!

Or if you do, then do two things:

1) double/triple check old part with existing part - there is at least two AK nozzles out there - long/short

PLUS certain manufactures make stuff slightly different so there is scope for stuff not to operate 101%

2) include what other bits you changed or altered as well - coz I'm having to include extra bits n bobs

Won't be the first time a thread continues to grow & grow - and this is growing even by my standards...

only to find out other facts emerge that complicate or change the initial issue/problem

The tappet plate moves back n forth to feed & chamber a bb

a nozzle is fitted that works with than gun/box/hop unit etc....

you only have about 7 to 7.5mm movement for tappet to retract and allow a 6mm bb to slip into hop

Also this needs a bit more than so the nozzle is pressing against the bucking lips to seal correctly

if it barely touches the bucking after chambering a bb the seal will blow

If you fit a nozzle too long then when it retracts it might not have just enough room to feed & chamber a bb into the hop unit

or not reliably 101% of the time - so when ever you think of replacing stuff you MUST CHECK & COMPARE stuff first....

Changing spring & nozzle "may" only add additional factors into the mix that was kind of ok

spring was 345fps originally, the box opened due to bearings coming adrift from piston head

(I suggested nylon spacer to save weight easily and less chance of working loose like bearings etc...)

Old nozzle could have worked lovely if you did fire at 33rps

New nozzle or new setup "could" have a feed issue or sector/delay on different sector gear on other gears

Hence did say could have just used the 30k motor instead of 40k motor - keeping it simple-ish

You was likely hitting 33rps on a 40k motor...

a 30k motor is 75% of a 40k motor (40 x 0.75 = 30 or 30 x 1.333333 = 40)

So take 33rps and multiply by 3/4 or 0.75 = 24.75rps for a 30k & 13:1 setup

Which is what was said at the start - the 40k motor was too quick with those gears

Simple change of motor, keep gears etc.... fix bearings/spacer (fps hardly changed on old spring)

Should have fed ok - well if it fed on a test @ 33rps then it should feed ok at 24.75rps so to speak

(of course all this basic maths bollox is only ever a very rough guide but there abouts)

minor work & little hassle messing about with any more stuff

piston was optional as I didn't know what was in there already or its durability

the bearing to spacer would save a fair bit of weight without going nutz swiss cheesing (more time/hassle) 

It is unlikely - but not completely impossible the 33rps was a misread on chrono but think it was correct

Normally if you are shooting at 33rps you are shooting at 33rps

if anything if you have a bb misfeed in stream of say 15 round burst then it will not say 33rps but say 24rps

Which if you are expecting 25rps then a misfeed issue drops it to say 18rps etc.....

I mean you could record the gun firing on your phone the play back the sound clip in audacity counting the spikes

Or you can use an app like - Paintball BPS meter

Though note it is fussy according to sound of your gun/muzzle/dry firing you bare box+motor

it might say 83rps on one test, then the next test it might say 23.75 the next time

If you have a rough idea of what to expect it does work well - when it actually works properly

It sometimes picks up the shrilly sound like a sewing machine that most AEG's sound like = odd results

Just saying if you record the sound or run the app it might indicate a different rof to possible misfeeding at chrono

Thing is with these bastid boxes you really don't want to be changing loads & loads unless it really needs it

AND when you do you must really really check everything as you go...

Forgot all these guru's making crap look easy - it is not that easy until you have f*cked up loads & learnt from mistakes

That is wisdom - the term wise after the event etc......

Don't complicate stuff too much by chucking more stuff into the mix all in one go

Even Legacy says you don't need to go nutz for modest builds with new aftermarket cylinder heads if ptfe tape works

Std piston head can be fine but just needs a better o-ring (though some are crap)

Nozzle yes often I'll change for an o-ring but check & compare the original against new nozzle for compatibility etc....

Tappet plate I might change only if say it doesn't hold the new SHS nozzle - like Cyma M2 boxes/tappets on SHS red M4

measure the thickness at front of tappet plate coz they do vary and might need sanding - not for feeding but sealing

(don't worry about this or think I'll change this as well - just saying a lot of crap is different and may not work as is)

So why bother adding more money & work checking/adjusting stuff you may not need to as well as add more grief ???

I'd be tempted to try and record or test the sound of box in app

see if gun misfeeds to arrive at low rof at chrono

if there might be a misfeed issue then you can open box, check the motor height/shimming and perhaps replace old nozzle

Or at very least get them both side by side or on table and stare very carefully at then side by side etc....

(digital calipers are a great measuring tool for checking stuff like battery dimensions, nozzle lengths and of course shim thickness)

I never said it was easy - but please stop keep changing stuff too much coz you are only making more work or confusing matters

 

[madmogga]

Ok sorry to keep confusing things I am learning about guns and forum posting at the same time. With the nozzle I did use a digital micrometre to check the length and checked seal and that the tappet return allowed bbs to enter hop up ok so I am 99% sure that feeding is not the issue and that shimming is. I changed the nozzle because I was not 100% happy with the seal on the old one so swapped it to one with an o ring. Might not get a chance to strip the box down again for a few days but ill post back on my long learning experience later in the week. Like I said at the start I am only doing this to learn so all these issues are great in one respect as I am getting to know all the problems and how to solve and check all at once.

 

[Sitting Duck]

It's fine - been there myself, steaming in, thinking this n that, trying to run before I can walk etc....

Oh it must be this, or OK I'll do this to compensate and before you know it, it is much worse than ever

Like I said my first couple of attempts were disasters

the next few were not much better but did work (for a while)

Then eventually learnt there is a bit more to this stuff than go faster motors, go faster gears and more juice

And there is so much to how it all carefully fits together exactly

Think this sort of sums up airsoft teching at times.....

 

[madmogga]

So I pulled everything apart again tonight, shimming was not good when I checked once everything was together two of the gears had zero play in them so stripped everything out again and started over. doing motor and bevel gear first. I did have a problem in that the height adjustment on my motor did not allow me to align the pinion and bevel so had to make a few adjustments to the motor cage. All shimmed a lot better and sounds a lot better although I still think it’s a bit noisy so maybe the shimming is still a little bit out. Popped it all back together with the 16:1 gears and the 40K motor no improvement on the RPS so I thought id check my lipo 3.5v/3.5v  wtf! I only charged it a week ago when I did all these mods and only been using it for testing 200 rounds max. I only had a half charged 9.6v with deans laying about so plugged that in and straight away sounded and ran better getting me 18rsp which I think on a 1600amp 9.6v half charge battery is a bit more like where I think it should be. Not sure if lipo is faulty or 3.5v/3.5v is normal after that short amount of use but am I right in thinking I should not run it down that much 3.8v minimum ?

why i never though to test the battery grrrr 

 

[Sitting Duck]

Lipo cells are 3.7v and can be charged up to a MAX of 4.2v

So a freshly charged LiPo will be 8.4v aprox

The cells have a charging range of 3.0v min to max 4.2v

above 4.2v per cell they are starting to overcharge and damage/deteriation may/will occur

if the cell drops to 3.0v or less some chargers will announce a charging error

this can sometimes be coaxed by slowly & lightly trickle charging the cells back above 3.0v

By then the B6 type charger should then attempt to charge the lipo as per usual

The cell(s) get charged up to 4.2v and balanced across the two/three cells which may equate to about 8.38v

In reality the cells may not be 101% balanced exactly but the charger attempts to balance the cells

(so don't panic if cell is 4.19v & other is 4.20v or 4.18v)

Cells can come off charge at a smidge over though they should not be much over the recommended 8.4v

(is your voltmeter 1001% accurate ???)

Rule of thumb - lipo's should be 8.4v max to about 6.4v or 4.2v per cell to 3.2v per cell

Often batteries get changed at lunch time anyway so they don't get too low and charge issues

(There are some newer ultra lipo's that can be charged a smidge more than 4.2v but usually 4.2v is the cell max)

Soon a fairly fresh 4.18/4.19v per cell lipo you rof should be XX rps

If your gun is still a tiny bit shrilly after checking motor height/bevel then it could be the motor angle

on a v3 with motor frame/cage if you slightly loosen the two screws on cage/box you should have a smidge of slack

by slightly altering the angle the motor meshes with the bevel you might be able to improve/worsen the gears meshing

(not a lot of slack but can make enough difference to quieten the gears a bit more)

 

[madmogga]

I thought I would post a quick update on the progress as I was still not happy with the motor height and my shimming and the RPS I was getting.

I purchased a new motor cage which is a lot better allowing for a lot more adjustment of the motor height, I also found the Action Army 30K motor meshed a lot better than the AEG boost 40k so rebuilt the gearbox with my SHS13:1 and the AA motor spending time doing the shimming (took me a good 2 hours) – put everything back together and gears now sound a lot better best I have ever had them, and I am getting a nice 21/22 rps which I am happy with.

Unfortunately, I now have other issues with the gun going into full auto while on Semi and the FPS down a bit but I think I know what these are, the semi auto issue I think is the gear shimmed a bit too high for the cut off level and the FPS drop due to the barrel / hop up unit not installed correctly –pushing the hop up in was a bit tighter than normal but as it was late I kind of just wanted to get it back together and test fire it so probably not aligned correctly giving an air leek ….

Nearly their ill sort the last few issues out tonight or tomorrow and hopefully will have a nicely tuned gun shooting just under my sit limit of 350fps  This was always just a project to gain experience an learn from mistakes and have really enjoyed getting stuck in, I have learned and gained a lot of experience especially with the help of this forum so a big thanks for all your help.