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 :lol: :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