Piston stripped

[Cheeky vimto]

Here my gun internals:

 

13:1 SHS gears

Stock spring guide

SHS red cylinder head

SHS plastic piston with corrected AOE

Hamsterfet

SHS lonex A1 supreme motor

Stock G&G spring (not sure what one, it was shooting around 350 at last skirmish)

8.4v nimh battery

 

I reshimmed my gearbox a few weeks ago to stop it from screeching so much. It's been shooting fine and sounding better for the reshim too. So today my order of a 11.1v lipo arrived. I threw it in and had a few test fired, maybe 50 shots. Then it happened, the sound of the gears spinning in the gearbox and it's not firing.

 

Could it of been a coincidence it went with the new battery?

Is it possible with the new battery the gears are engaging before the piston has fully returned?

 

I'm going to get a new one tomorrow but I don't want it last 2 minutes before failing.

 

[Sitting Duck]

Yes

 

Looks like deffo PE to me

 

My guess you hit 23 on 7.4 and then near 35

Piston didn't fully return and stripped 5 4 3 gears

 

Or pistons are n pitch was not good was a few bad batches of SHS pistons a while back but my main guess is too fast & PE happened

[Sitting Duck]

Update saw high speed gears

 

So hitting 27 on 7.4 then near 40 ???? On 11.1v

Yeah that is fully taking the piss

 

To run that quick you gotta short stroke 2 teeth n use m120

[RR01]

If you are going to use an 11.1V Lipo then you really need a fully upgraded top of the range setup to take the stresses that the additional power provides over a standard nihm battery. If you want to go Lipo then a 7.4V would have been a far safer conversion and would have given power equivalent to a 9.6V nihm. Sticking an 11.1V in there is like connecting it up to a fully charged car battery pushing out about 13.4V, way more than a standard setup can handle safely.

[Cheeky vimto]

Update saw high speed gears

So hitting 27 on 7.4 then near 40 ???? On 11.1v

Yeah that is fully taking the piss

To run that quick you gotta short stroke 2 teeth n use m120

 

That's what I just read somewhere too. Is it possible to get under 350fps on a m120? I've read m120 can give out 400fps

[Cheeky vimto]

If you are going to use an 11.1V Lipo then you really need a fully upgraded top of the range setup to take the stresses that the additional power provides over a standard nihm battery. If you want to go Lipo then a 7.4V would have been a far safer conversion and would have given power equivalent to a 9.6V nihm. Sticking an 11.1V in there is like connecting it up to a fully charged car battery pushing out about 13.4V, way more than a standard setup can handle safely.

I was under the impression if I had a MOSFET, good shim and AOE I'd get away with it. My piston is a SHS with a metal last tooth, it's not stock.

 

I understand higher ROF means things wear out quicker but 50 shots is ridiculous, pre engagement has got to be the problem.

[sp00n]

RIP piston

[Sitting Duck]

1,000,000 shots on semi no problem

Or

50 shots on full auto = BANG

it ain't one single shot it is piston not returning in time for shot 2 3 4 5 etc on auto

 

Can happen on semi if she double fires but still not as quick as full speed auto

 

Be grateful you had plastic piston, all steel teeth piston could have a much bigger BBBBAAAAAAANNNNNGGG

and gears even motor pinion could have gone bust

[Cheeky vimto]

can you get different sized ports on a ported cylinder? Was thinking if I got a bigger ported cylinder is wont compress as much air and reduce the FPS?

 

Here's my current cylinder;

 

[Samurai]

Siting Duck is right. That piston didn't return in time. Maybe it didn't move free enough, or the o ring had a bit of resistance moving the other way, or it's simply too heavy with bearing inside, etc.

 

Short stroking a piston takes away a lot of fps.

 

The ports' size on the cylinder doesn't affect the compression. Well, bigger ports let the compression build up quicker, but that's already nominal on the normal ports too.

[Cheeky vimto]

1,000,000 shots on semi no problem

Or

50 shots on full auto = BANG

it ain't one single shot it is piston not returning in time for shot 2 3 4 5 etc on auto

Can happen on semi if she double fires but still not as quick as full speed auto

Be grateful you had plastic piston, all steel teeth piston could have a much bigger BBBBAAAAAAANNNNNGGG

and gears even motor pinion could have gone bust

 

That's the original reason I went with plastic. The guy at the shop advised against metal if I'm doing my own work

[Cheeky vimto]

Siting Duck is right. That piston didn't return in time. Maybe it didn't move free enough, or the o ring had a bit of resistance moving the other way, or it's simply too heavy with bearing inside, etc.

 

Short stroking a piston takes away a lot of fps.

 

I could lose 50fps with short stroking?

[Sitting Duck]

That's what I just read somewhere too. Is it possible 6to get under 350fps on a m120? I've read m120 can give out 400fps

Buy 3 steel piston remove last 2 teeth so you got only 1 steel left

 

Then remove the FIRST 2 teeth from sector gear

NOT LAST 2 or you mess tappet timing

 

Fit m120 spring, might be m115 but try 120 first

[Sitting Duck]

Do 1 tooth removal first on m120

 

You can always remove another if she is way over

 

Think m110 and 1 tooth might still be asking for PE

[sp00n]

I could lose 50fps with short stroking?

 

The normal way with short stroking is to fit a bigger spring since the piston wont be traveling as far, thus you get the same FPS

 

EDIT SD beat me to it lol

[Cheeky vimto]

Buy 3 steel piston remove last 2 teeth so you got only 1 steel left

Then remove the FIRST 2 teeth from sector gear

NOT LAST 2 or you mess tappet timing

Fit m120 spring, might be m115 but try 120 first

Is there any other way, don't really want to be messing with the gears.

 

Might just get a a couple Pistons tomorrow and go back to my nimh for now. I've got a game on Sunday and need this gun.

[Sitting Duck]

No real other way I'm afraid for higher speeds

 

I have found out the hard way like you what happens

Is why I say 25 to 30 unless you do your homework

Any battery can be pushing 1 or 1.5v fresh off charge

Your spring will lose tension also in 6 months

So if you get away today you may not scrape by in 6 months and a fresh battery can just PE

 

anything over 30 is close IMHO

And it "may" need a bit of work

35+ is deffo taking the piss

 

US forums can say yeah use 120 spring

But is too hot for UK sites

 

Soz

[Cheeky vimto]

No real other way I'm afraid for higher speeds

I have found out the hard way like you what happens

Is why I say 25 to 30 unless you do your homework

Any battery can be pushing 1 or 1.5v fresh off charge

Your spring will lose tension also in 6 months

So if you get away today you may not scrape by in 6 months and a fresh battery can just PE

anything over 30 is close IMHO

And it "may" need a bit of work

35+ is deffo taking the piss

US forums can say yeah use 120 spring

But is too hot for UK sites

Soz

They say each tooth you take off takes about 15-20fps away. If I go for m120 if it worth trying? I don't want it to be still too high and I've messed up the gears.

[Cheeky vimto]

Decided to get the same piston and go back to what I've been using. I'll also get a full metal rack and short stroke it next week. My problem is I don't have a Chrono

[Sitting Duck]

If you was local I'd lend you mine m8 when ya ready to do final test

 

TBH - that setup you got/had will give out aprox 27rps on a decent 7.4v lipo

(not just from maths but Sp00n did the very same setup with 13:1 fet/deans etc... on 7.4v)

 

if anything I know it sounds bollox but very few instances would absolutely demand 11.1v

you could hit 30+ on 12:1 with thick wire/deans/fet and also extra solder on motor connectors at the "elbow"

Then with that there would be very very little resistance in the wiring so max juice is ensured to motor

best fet install is to do the wiring in one wire from motor to battery deans on positive

then only time negative breaks is at fet, fet signal supply spliced from positive so the wire loom is as full & unbroken/least connectors as possible

 

I feel if you got a good say 30c 7.4v 3000mah battery you would of still got an improved rof without shreading piston

 

you went from say 18:1 stock gears of 20rps with fet/motor to 27 on 13:1

though on old skool nimah you may not of hit this and got only 23

(nimah's don't have the same burst or C or oooomph that lipo's can have)

then the extra cell took the 27 you would of got on say a 25c 7.4v lipo to 50% more = 40rps = bang !!!!!!!!

 

Also what we all need to remember is that your box will have a probable life - just like car

eg: 100,000 miles or shots - this is just a rough figure but lets say 100k

by firing at 40rps and driving a car at max speed screaming through the gears you will hit that xxx figure much quicker

Well in actual fact your gun/car may only reach 60 or 70k if you take the piss

 

It is most likely not a super duper cnc reinforced box so it ain't designed to be pushed that far for too long anyway

especially as a starter box shoots at say 15rps - you start to get the idea now that going too fast may not be wise in long run

 

get gun working again with another piston (plastic 1 metal or 3 metal max)

go to your site - chrono and shoot away

 

at lunch as a m8 if they got a good 7.4v lipo on deans etc.......

can I just borrow that 25c/30c 7.4v a sec please......

 

pop that in your gun and I'm pretty sure you will see/hear a slight increase in response/performance over the nimah

if happy and she don't break - then perhaps get a good juicy 30c 7.4v instead of 11.1v

your gun will love you for it and should be a nice long loving relationship with less chances of breakdowns

[Cheeky vimto]

If you was local I'd lend you mine m8 when ya ready to do final test

 

My local shop is about 20 minute drive away. They let me use there's but that's a ball ache driving there and back each time. I'm thinking m120 with 3 teeth off, the go Chrono.

[Sitting Duck]

Go with two teeth first as all gun builds are different, if you really really want to short stroke

 

if you are just a tad tad over say up to 360/365 then you "could" leave her cocked over weekend to lose a bit of tension

then you "may" get to 350 after she lost some spring tension perhaps

 

to remove 3 may be a tiny bit too much and you can't put teeth back on

also each spring and deffo each gun is different - shs m120's may be more like a m125 brand new out of box

I also think unless you are sure your G&G spring may not quite be hitting 350 especially if it was still old stock G&G spring

(usually they hit 330 out of box and drop a little more after a while)

 

to remove 3 teeth you gotta get a half steel/plastic one - and you know not to get a full metal tooth piston

 

I gotta ask this though:

 

How friggin' fast do you want to shoot ???

Are your mags gonna feed ok at near 40rps ???

plus there comes a point when you won't notice such an increase

eg: 15 to 20rps - deffo notice but 35 to 40rps not really easy to notice the difference

 

me personally get a 3 metal piston and get gun working on nimah's

see if you can try out a 30c 7.4v for a while - maybe that would be safer nearer 30 than mental 40 with all the work and possible mag feed issues, plus if you stay sensible then you can just pop in new piston and get going again without all the extra work for higher speed

 

Higher speed builds - especially the more crazy stuff will require lighter pistons and plastic pom piston heads

lose piston bearing & swiss cheese (in moderation) - this all reduces weight to help piston return quickly

me I avoid piston bearings - they can come undone but also that is about 3.5gms saved by dropping bearings

use a bearing spring guide instead to avoid spring twist - same as piston bearing but means piston is lighter

avoid heavier alluminium piston heads in very high speed builds as they can weigh 6 or 7gms on the double O-ring kind

 

a full complete piston can weigh 15gms to 30gms on full metal piston with bearings & double O-ring piston head,

all that extra weigh gained/lost can make quite a difference to how quick the piston returns

so unless you want to do more homework and all that - I'd try a 7.4v 30c battery first perhaps

 

And if you are sailing that close to wind or PE you do NOT want a full metal piston

half/half would be max - especially as we both are still learning

 

you must have a weak point in your box - the plastic pick up & first few teeth at least

if she PE's you do minor damage usually just to piston

full metal & PE = MEGA BAAAAAANNNNNNNGGGGGGGGG

 

yes higher speed builds can/do use metal for strength and long life piston but they have well n truely short stroked

or using only half the teeth like 8 steel teeth on DSG's - but they know what they are doing

 

Us noobs learning by our mistakes or rather breaks are not so talented and clever techy mofo's so best play safe

I know I do talk bollox most of the time but trust me I have learnt a bit lately by making many mistakes too

especially when taking the piss a bit

[Cheeky vimto]

Go with two teeth first as all gun builds are different, if you really really want to short stroke

 

if you are just a tad tad over say up to 360/365 then you "could" leave her cocked over weekend to lose a bit of tension

then you "may" get to 350 after she lost some spring tension perhaps

 

to remove 3 may be a tiny bit too much and you can't put teeth back on

also each spring and deffo each gun is different - shs m120's may be more like a m125 brand new out of box

I also think unless you are sure your G&G spring may not quite be hitting 350 especially if it was still old stock G&G spring

(usually they hit 330 out of box and drop a little more after a while)

 

to remove 3 teeth you gotta get a half steel/plastic one - and you know not to get a full metal tooth piston

 

I gotta ask this though:

 

How friggin' fast do you want to shoot ???

Are your mags gonna feed ok at near 40rps ???

plus there comes a point when you won't notice such an increase

eg: 15 to 20rps - deffo notice but 35 to 40rps not really easy to notice the difference

 

me personally get a 3 metal piston and get gun working on nimah's

see if you can try out a 30c 7.4v for a while - maybe that would be safer nearer 30 than mental 40 with all the work and possible mag feed issues

 

Higher speed builds - especially the more crazy stuff will require lighter pistons and plastic pom piston heads

lose piston bearing & swiss cheese (in moderation) - this all reduces weight to help piston return quickly

me I avoid piston bearings - they can come undone but also that is about 3.5gms saved by dropping bearings

use a bearing spring guide instead to avoid spring twist - same as piston bearing but means piston is lighter

avoid heavier alluminium piston heads in very high speed builds as they can weigh 6 or 7gms on the double O-ring kind

 

a full complete piston can weigh 15gms to 30gms, that extra weigh gained/lost can make quite a difference

so unless you want to do more homework and all that - I'd try a 7.4v 30c battery first perhaps

 

I'm going to my local today to pick up another piston and put it back to how I had it just for this weekend.

 

My last game where I was chrino'd was strange. My first shot came in at 374 then it fluctuated; 330,365,340,370,345,38,350. All those reading were off the stock G&G spring. I didn't think they were going to let me play but as the averages were dropping they allowed it.

 

I want it to be as quick as I can make it. It's a hobby, and a part of that for me at least is pissing about with the toys

I will short stroke it, it's just unfortunate this has happened 2 days before a planned game. My friend has a couple 7.4 lipo's so I might try one over the weekend. And I right in thinking it shouldn't increase ROF, just trigger response?

[Sitting Duck]

I'm going to my local today to pick up another piston and put it back to how I had it just for this weekend.

 

My last game where I was chrino'd was strange. My first shot came in at 374 then it fluctuated; 330,365,340,370,345,38,350. All those reading were off the stock G&G spring. I didn't think they were going to let me play but as the averages were dropping they allowed it.

 

I want it to be as quick as I can make it. It's a hobby, and a part of that for me at least is pissing about with the toys

I will short stroke it, it's just unfortunate this has happened 2 days before a planned game. My friend has a couple 7.4 lipo's so I might try one over the weekend. And I right in thinking it shouldn't increase ROF, just trigger response?

 

check your mags can feed at silly speeds - remember faster rof = shorter life (usually)

 

trigger response & rof "kind of" go hand in hand though

YES THEY ARE DIFFERENT - before anybody flames me

but they are "kind of linked" in the way a 40rps gun will fire/respond much quicker than a 20rps

 

Good decent lipo's piss all over the old skool - them nimah's don't have the ooomph that decent higher burst lipo's have when you pull the trigger

mental techy's go for 40-60c+ lipo's but for a tweaked gun you should aim for 25c min, pref 30c should be fine for most

 

a good lipo - check the burst or C rating will ensure she is supplied with enough juice off the trigger and if your wire is upgraded it will keep chucking juice to that greedy motor and run much better than 8.4v - honest

 

I have bought some 11.1v's and also some 9.9v LiFe's too but if I tweak the gun properly I can't see me using the higher batteries that much when good 7.4v's provide great results, plus can get the 7.4v's cheaper and coz they aren't so fat as 11.1v's I can get higher burst/amp batteries in same space/price range as 11.1v batteries

 

your gun is fluctuating a bit though 330 - 370 maybe 38 - you mean 380 - that is quite a bit

check all seals - especially piston's o-ring & cylinder head is mega good

370 or 380 - yeah that ain't no m100 in there

[Cheeky vimto]

check your mags can feed at silly speeds - remember faster rof = shorter life (usually)

 

trigger response & rof "kind of" go hand in hand though

YES THEY ARE DIFFERENT - before anybody flames me

but they are "kind of linked" in the way a 40rps gun will fire/respond much quicker than a 20rps

 

Good decent lipo's piss all over the old skool - them nimah's don't have the ooomph that decent higher burst lipo's have when you pull the trigger

mental techy's go for 40-60c+ lipo's but for a tweaked gun you should aim for 25c min, pref 30c should be fine for most

 

a good lipo - check the burst or C rating will ensure she is supplied with enough juice off the trigger and if your wire is upgraded it will keep chucking juice to that greedy motor and run much better than 8.4v - honest

 

I have bought some 11.1v's and also some 9.9v LiFe's too but if I tweak the gun properly I can't see me using the higher batteries that much when good 7.4v's provide great results, plus can get the 7.4v's cheaper and coz they aren't so fat as 11.1v's I can get higher burst/amp batteries in same space/price range as 11.1v batteries

 

your gun is fluctuating a bit though 330 - 370 maybe 38 - you mean 380 - that is quite a bit

check all seals - especially piston's o-ring & cylinder head is mega good

370 or 380 - yeah that ain't no m100 in there

 

 

Picked up another plastic SHS piston today and reassembled. It doesn't sound as smooth as it did do before the lipos but I got it Chrono at my local and it's shooting between 345-350. I'm going to leave it like that for now.

 

I might just leave the 11.1v lipo's alone and go for 7.4v. Have you ever tried to send back stuff to component shop?