gearbox lock up

[Chopper92]

Hi All,

Just upgraded the internals on my Umarex H&K UMP.The problem is once i installed all the upgrades and went to test it the gearbox will lock up and not turn. I therefore took it apart to look for problems.Couldnt find any and completed regreased the system. It continues to lock up.

The upgrades ive installed are

4/5 ported cylinder

new reinforced piston.

new double o-ring piston head.

13:1 ratio gears

High Speed High Torque motor

Now ive run the system off a 7.4v NimH to test. Would this be the problem for it not turning ? e.g Not enough power? The motor turns outside of the gearbox when attached to this battery.

Or are the some other problems i need to look for?

Cheers

 

[Sitting Duck]

7.2v or 8.4v nimah ???

I've run 8.4 & 9.6v nimah on a shs high speed but that was with stock 18:1 gears in a G&G

your ratio/speed has increased by about 36% more work though

(18.65 divided by 13.65 = 1.366)

so yes that could be pushing it, not gonna say it is like having a m130 spring in there

but reckon about a m120 easpecially at start standstill

another matter might be if piston is bottoming out on spring guide or full spring compression

but this would normally happen is bearing spring guide and bearing piston/spacers ott

and some springs with thicker wire/coils won't compress as much as other thinner/weaker springs

daft thing but spring is fitted correct way round - it can make a difference

charge up battery or see what you got for more grunt but careful you don't blow fuse

just a quick test or two to see if she will cycle with a bit more juice

what motor in there - neodym ???

if motor has the oomphhhhh, and no mechanical lock up on piston travel/spring compression

then most likely weak or not fully charged nimah could be issue

As you already did a lovely to work on G&G I will assume it wasn't down to bad fitting of them components

but all the same that may need to be considered

if its the v3/g36 type box in your ump - at least you can test it a little easier than with the G&G v2 putting it back in receiver etc....

 

[Chopper92]

Hmm Might switch back out to my stock gears, see if the system cycles then i will know if its the battery or poor fitting

 

[Sitting Duck]

Another possible consideration and correct me if I am wrong here....

On your G&G it probably was just a "service" or replacement of a part or two

However you have replaced the stock gears with another set and so it could be shimmed a little incorrectly

Specifically the bevel could be too low and when the motor is wound in the pinion is forced hard against bushing/bearing

This creates a great strain on its own when cycling and is not good for your whole box/motor

This was my mistake (along with others) when I was having real grief on my first few gearboxes

A GENERAL RULE OF THUMB - note general rule of thumb not a gospel to follow but along the line of what you can expect....

middle/Spur gear a thin shim behind it if using bushings - medium shin behind it if using bearings

bevel gear - hardly anything on top of it - thinnest possible shim maybe 2 or thin medium shim if using bearings

BUT OFTEN VERY LITTLE ON TOP OF BEVEL GEAR

Bearings will need more shims than bushings btw as they are thicker

sector - shimmed as needed

rough guide on hand closing box you should see sideways movement on all gears of aprox 1mm

when tightening box up - I'd say nip screws using just finger and thumb on screwdriver to avoid going nutz and stripping threads

when box is tightened up this 1mm play will reduce to 0.5mm - aprox

I always hold the box and 2 out of 3 bearings - shake box and should hear the 3rd gear click as it moves from shaking

repeat on all gears to hear and check by pushing through with screwdriver but sometimes you don't notice it vividly moving

always the spin test on gears too - just I like to hear the play sound so to speak

numerous things or tips I do like backing off a screw at a tiny bit at time to pinpoint any tightness on which gear

All of this means f*ck all if the gears are not "stacked" or arranged correct height to each other

Oh there's loads of little things to say/do & test and thie above is not a complete guide or list on how to shim

but it is very important not to shim bevel gear too low or even slightly low

 

[Sitting Duck]

For what little it is worth......

Gear ratios are never quite what they say on them and often the 18 is a 18.65

or 12 is really 12.65:1 ratio

12:1 & 13:1 gears are little too much imho - they increase your fire rate by 35 to nearly 50%

but it is more work for motors to run through especially from start

due to fact 16:1 are in fact more like 17.25:1 they offer less improvement that first thought

(often an expect 10-12% turns out to be 8% improvement not much but still mugged)

for that reason I think a 15:1 - which I haven't seen around

or a 14:1 set might offer a balance of about 28%-ish for performance wise

but still it seems to common or popular options are stock 18:1, 16:1 or 13:1

(or must have 12:1's for nutter speedsters trying to over compensate for something)

End of the day if stock gears are good ones then very often leave them in there along with a few other stock bits like piston

new bits to help seals like ptfe, or new cylinder head, o-ring and o-ring nozzle plus aoe is what will help

possible wire in fet - use deans and perhaps good wire and when ready a oomphy neodym motor will sing no problem

Gun doesn't go too fast to crap out too quick and owner is happy for very little work/money in the end

Yes 13:1's on higher speed setup's but a bit more work involved getting that to operate well is needed

faster n faster on m100 spring and she double cylce's etc.... risk of PE may get closer plus gun will wear more

13:1 nutter builds when you start to push it will deffo need short stroking past 30rps

thicker wire mofo batteries etc...............

on stock stuff/gears you can get to 20rps on 7.4v and 30 on 11.1v but as I say at 25 to 30rps more homework is needed

the above figures are on fast torquey neodym motors - these can be anywhere from 10% to 50% over stock motor's performance

so don't flame me if you don't hit the exact figures I quote coz builds are very different and I always use thickest wire and deans/fet etc....

 

[Chopper92]

put the stock gears back in and its cyclying beatifully with the new motor, and cylinder etc but i fear they may not last very long. So the issue seems to be something to do with the 13:1 gears. I suspect its the smaller battery not giving out enough grunt for the motor to turn them. Therefore i will get a 11.1v in there at some point and see then !

 

[Sitting Duck]

OH FOR FFS DON'T DO THAT !!!!!!!

seriously - soz about shouting

your rate goes up by 36% then you boost it by 50% on 11.1v

and a very good chance of BANG !!!!!!

try it on 7.4v then gauge what your rof is.....

eg: say 13rps stock, could go to 14 on deans or 15 if fet n rewired

then up a third to 20rps on 7.4v with 13:1 gears

which then will give you an expected 30rps if using a 11.1v

(note the 50% boost from 2 cell 7.4v to 3 cell 11.1v)

at 30rps on STOCK MOTOR is getting risky

if you got a neodym in there that 30 could jump up from 33 to 45-ish (10 to 50%)

though to get to 45 you would have to be using very thick wire

but 35 maybe near 40 "could" happen

I stripped a 2 tooth short stroke piston with m120-ish spring pushing 11.1v to 45rps

and it stripped straight away

30 is really taking liberties on full stroke m100 spring in my book

so I really really really advise anyone to please please test out your gun on say a 7.4v 25c lipo

even a block type battery just taped on there to test it out first

I stand by my most of my maths - it can vary a bit depending on motor and wiring/connectors

but if we take a stock gun and work out maths again slightly different way.....

stock gun = 13 rps on 7.4v lipo - chuck in 11.1v lipo (mosfet is good idea but anyway) = 20rps

20 rps then 10% to 15% for deans/wire/fet = 23 aprox

23 x 1.36 due to 13:1 gears puts you at 31.28 - take that back to 30 due to 13rps x 1.5 from lipo is actually 19.5

but you get idea and like I said this is worked out on a decent stock motor - not a neodym nutter

But even armed with this history of breaking pistons n crap

I still end up pushing it or taking the pi$$ - only now I expect it to break a bit

or understand the risks a bit more

 

[TheGrover]

+1 on the 7.4, unless you're making a bb hose a 7.4 is plenty power

 

[Sitting Duck]

put the stock gears back in and its cyclying beatifully with the new motor, and cylinder etc but i fear they may not last very long. So the issue seems to be something to do with the 13:1 gears. I suspect its the smaller battery not giving out enough grunt for the motor to turn them. Therefore i will get a 11.1v in there at some point and see then !

As long as you have done AoE she will be fine

if you don't and you start taking the pi$$ that initial pick up tooth just snaps off the back very very very quickly

well twice on 9.9v life & 11.1v it happened before the aoe penny dropped

OOOOOoooooohhhhhhh is that why they keep going on about it

yup learning by my many many numerous mistakes - still learning btw

you got new motor in there, see what she is shooting at ROF wise and decide how fast you go

the gears if battery can cycle them will give you 36% max increase

the 11.1v will give you up to 50% increase on stock gears atm.....

so based upon a bit of common sense maths work out your requested rof

and decide how fast n how you get there sir

 

[Sitting Duck]

Just nigh on finished my on/off Raider project.....

A while back I looked at short stroking and was reading up wrong info on some sites to take off BACK teeth

Armed with this incorrect knowledge I cut of 2 BACK TEETH and was getting weird mofo results

effectively by removing the teeth off back it was running fast on a lovely SHS 12:1 set of gears

but nozzle didn't have enough time to seal against hop/bucking.....

Crap - just boned a nice set of gears up and 12:1 gears are different to normal gears so can't just use an old 18:1 sector

So they sat there reminding of yet another one of my failings, screw me taking the first bit of info as gospel...

Anyway after another full stroke piston stripped I thought about trying those 12:1 boned gears with bits n bobs and stuff

I had learnt from the HC05 DSG so to speak.....

I need to get trim up the tappet plate to release earlier so shortened the length of the tappet plate fin

but to ensure she opened long enough to feed bb's at higher speed a delay clip would be wise

Last week or so all was working but a plastic/steel piston rack stripped at 45rps dry firing straight away - damn it

2 teeth removed btw on piston.......

So I used same all metal teeth rack like on DSG but took off 4 teeth and a further 2 teeth on sector at START of sector

where it should be removed..... learning by mistakes is good but costly and annoying sometimes

To compenstate for 2 more teeth being removed an additional 5mm spacer was added - mainly coz couldn't be ar$ed

to look for a m130 or something.....

The idea was to build a SSG G&G that would perform faster on 7.4v than the stock HC05 DSG does on 11.1v

and it does hit 33rps but that is with some seriously thick mofo wire and a mental neodym motor...

it does fire on 11.1v at 45rps but it struggles to feed - well hardly feeds at all due mainly to 2 things....

The tappet plate timing would be better if I hadn't screwed it up in first place for ultra higher speeds

plus

On assembly I noticed the tappet spring itself was maybe a little lighter than other boxes so that won't be helping at silly speeds

But I did what I set out to do and got to make use or good one of my earlier gearbox balls ups

I will probably drop the motor to a slightly slower torquey motor and perhaps settle for say 26/27rps for more sensible lasting fun

yup it was the horrid green 2-tone one I got cheap a while back - jeez that was fun stripping that off the raiders ris

(well technically that box is still stock this was another CM with stripped piston but same meat/gearbox)

To get to this stage meant I screwed up LOADS of times but have learnt not to go too nutz

like I say will probably drop a slightly slower torquey motor in there to keep her at 26rps ish and hopefully last a while