miserydrift 71 Posted January 17 Share Posted January 17 Well my cyma's piston has crapped itself,any recomendations on a upgrade piston? also thinking of replacing the gears shimming etc as im assuming the issue has been the gears been able to move and jump cause it to do that,i dont mind throwing a little bit of money at it as i dont have much invested in it so have a rough budget of bout £70 for upgrades/replacement parts once i have the mechanics all sorted will move onto cosmetics Link to post Share on other sites
Supporters Sitting Duck 3,394 Posted January 17 Supporters Share Posted January 17 That is "likely" PME Premature Engagement gun cycling too fast, sector attempts to engage the piston before it has fully returned and crunches into the rack on the 3rd/4th tooth etc... Plastic teeth being weaker start to strip, it happens once or twice, it gets worse = f*cked If this happens on a full metal rack piston then metal gears/rack tear themselves off (something has to give/fail in the end) It can also happen with a jammed BB, so the newbie mistake is to keep firing on auto to clear it even mag out - full auto - CRUNCH The jammed BB has plugged the compression like a syringe and this slows the piston's return = PME or something just failed, pear shape tits up and crunch - stuff happens but usually that looks like possible PME likely cycling too quick or jammed BB or both Change piston to metal rack Cyma, buy new o-ring could buy new cylinder head, but 7 or 8 wraps of ptfe works well if done neatly leave the gears, maybe buy a SHS HT motor but NOT a high speed motor that'll do for internals clean barrel, use decent bb's - really makes a difference & prevents jams from egg shaped bb's (or big seams on cheapo bb's causing jams in tbb/bucking) if you want zci hop, maple leaf bucking & red nub barrel should be a half decent tight bore one Link to post Share on other sites
miserydrift 71 Posted January 17 Author Share Posted January 17 was trying to figure out what you meant by pme loool perfect and again thank you for your time replying as far as i can tell it has had a hop rubber changed to a maple leaf and i think its got the red nub installed as theres an near empty pack with just the black one Link to post Share on other sites
Supporters Sitting Duck 3,394 Posted January 17 Supporters Share Posted January 17 Ahh - good stuff the previous owner bought the twin pack nub hard black/soft red you need to check it was fitted OK by plopping a bb into hop unit then it should only need a light moderate push with match/cocktail stick or very carefully a thin screwdriver, just something to pass the bb through lips if it is tight then that will misfeed or mischamber the bb causing misfeed/jams... somewhere in this vid he goes through the "push test" DON'T GO MODDING SHIT !!! it is just to show tight bucking lips causing feed issues tbh just test the lips are not too tight - that's all I doubt if you got tight bucking, but always worth a check coz you will have issues feeding again do not do anything like modding hop etc... just check the lips are not too tight on bb push test - that's all Link to post Share on other sites
miserydrift 71 Posted January 17 Author Share Posted January 17 will give that a check in the morning thank you yeah i wouldnt go modding things without posting here first bud i dont know enough yet to even contemplate that and only got the basic theory of how the hop works havent delved in to that side further yet lol Link to post Share on other sites
Supporters Adolf Hamster 3,753 Posted January 17 Supporters Share Posted January 17 Going from your other thread you're running that thing on 11.1v In which case i reckon @Sitting Duck is spot on about the pme but i'm wondering if this is a weak spring as the culprit. ive seen a cyma eat a piston like that was fresh out the box, 11.1v but a half-assed "fps downgrade" by the shop with it spitting out 0.5j had the piston chewed up bad within 30 minutes (weak spring means it doesnt have to be spinning as fast for pme to be an issue so the stock motor on a hefty battery was fast enough) When you get the new piston in might be worth checking the fps. If you get very consistent (ie each shot doesnt change much in fps) but low readings then that might be your culprit. Dont know how confident you are with tinkering but there's a few tips and tricks for dissassembly/gearbox checks here: You dont need to go ham with trying to change things like aoe/shimming etc just yet, Just keep the shims in the positions they were originally. but at least that should let you know what to expect so you dont end up with a spring guide pinging its way into the aether the moment you pop it open. Of course this is assuming the gearbox is all stock and this isnt as simple as the previous owner dropping a spicy motor in there. Sitting Duck 1 Link to post Share on other sites
Supporters Sitting Duck 3,394 Posted January 17 Supporters Share Posted January 17 8 minutes ago, Adolf Hamster said: Going from your other thread you're running that thing on 11.1v In which case i reckon @Sitting Duck is spot on about the pme but i'm wondering if this is a weak spring as the culprit. ive seen a cyma eat a piston like that was fresh out the box, 11.1v but a half-assed "fps downgrade" by the shop with it spitting out 0.5j had the piston chewed up bad within 30 minutes (weak spring means it doesnt have to be spinning as fast for pme to be an issue so the stock motor on a hefty battery was fast enough) When you get the new piston in might be worth checking the fps. If you get very consistent (ie each shot doesnt change much in fps) but low readings then that might be your culprit. Dont know how confident you are with tinkering but there's a few tips and tricks for dissassembly/gearbox checks here: You dont need to go ham with trying to change things like aoe/shimming etc just yet, Just keep the shims in the positions they were originally. but at least that should let you know what to expect so you dont end up with a spring guide pinging its way into the aether the moment you pop it open. Of course this is assuming the gearbox is all stock and this isnt as simple as the previous owner dropping a spicy motor in there. luckily.... he has the QC Cyma box with mosfet in there which helps to open up with spring removed (ahhh the fun explosion I had opening my first SRC box) it is a weird non-reinforced at back Cyma - 13:1's will go straight in (ergh - keep gears as is btw, don't change more than you need to) A SHS piston "might" not bind like the reinforced Cyma boxes (both v2 & the .028 v3's - SHS pistons bind in those) Still just replace with Cyma piston is safe option imho & reassemble Blue tappet is way better than old clear tappet Cylinder head is same floppy fit - only in blue than white Piston head - sometimes a silent mushroom type other times it is same concave piston head now in blue than white (still needs o-ring stretched/changed for compression) Nozzle is same std type non-o-ring but in blue than clear got a 517 in November - blue stuff inside 8mm cross bushings "seem" to be slightly different/revised or new source, tiny bit chunkier, slightly less shimming room than older original 8mm cross bushings I remember box was still reinforced at back, mod req for 13:1's has a ARL window in it now it didn't have before Std trigger switch - OMG this is blue and the shuttle/trolley has loads of lateral play in it, I slightly pinched the contacts straight (less flared) shaped them to touch but not grab the trolley... Fucking thing was moving sideways all over the place missing the contacts at times Don't remember the old white trolley switch as loose as this So changed the switch/trolley due to lots of lateral play in it The sloppy blue switch in the new revised cheap 517/5xx M4's is my only gripe (and still uses the prongs at selector plate) need to often carefully widen the switch mounting "eyelet" if using other v2 switches Still got the silly safety arm to undo prior to opening box But overall pretty robust stuff inside with mostly minor improvements (still crap o-ring & loose as fuck cylinder head) Not a fantastic improvement, nor say another half a point but say an cheap as fuck 8/10 became say a 8.25/10 Link to post Share on other sites
Supporters Adolf Hamster 3,753 Posted January 17 Supporters Share Posted January 17 after looking at this thread without being sleep deprived i realised how has he photo'd the piston if he hasn't already taken it apart.... Link to post Share on other sites
Supporters Sitting Duck 3,394 Posted January 17 Supporters Share Posted January 17 Them Cyma QC boxes are something else when the piston shits the bed they eject the piston for you nah - get some more kip he said he opened it up to check what was fucked here: click arrowy bit to see the reply... 9 hours ago, miserydrift said: so decided to crack the gearbox open and take a look myself as to why it shit the bed on just 5 rnds on semi ??? dunno if the Cyma bespoke mosfet is an AB type or just a std mosfet - really haven't a fucking clue could be std, could be AB with the extra bit of pcb bollox if AB then it should have made the piston stop on a tanner after cycle & not PME like a std mosfet could but reckon it was a jam on nutty auto burst that likely killed it or seriously injured it at some point (most PME wrecks occur on auto - well mine have when taking the piss & even with planning - still wrecked on auto seeing oooh this goes quick - oh FUCK) Link to post Share on other sites
Supporters Adolf Hamster 3,753 Posted January 17 Supporters Share Posted January 17 look i have the ability to self-jetlag under normal circumstances and lockdown aint helping Sitting Duck 1 Link to post Share on other sites
Supporters Sitting Duck 3,394 Posted January 17 Supporters Share Posted January 17 3 minutes ago, Adolf Hamster said: look i have the ability to self-jetlag under normal circumstances and lockdown aint helping I'm wide awake most times but still veer right off the actual subject so far as I forget what the bloody original question was... sorry what was I saying ??? Ya probably right 11.1v used causing rapid shredding guessing these issues is a fun challenge at best of times I love it when the poster just mentions they was running it on 14.8v LiPo and you then think - oh just fuck off now or - yeah it might be a short as sparks were flying out the back blowing the fuse so I just used silver foil to bypass it - WTF ??? or yeah it did make a big crunch, jammed up but now it is working but nozzle doesn't move much you know the 3 pages in & then you start getting the rest of info how shit broke not directed at OP, has been fairly up front - just sometimes it is a major guessing game THEN the real truth comes out - wtf didn't you say that at beginning ffs !!! Sorry what was question again - I'm waffling again Link to post Share on other sites
Davegolf 799 Posted January 17 Share Posted January 17 @miserydrift I would fit a similar plastic / metal teeth combo piston, BECAUSE if shit hits the fan, like it has for you, the damage is limited to just a new piston. If you run full metal teeth piston and what has happened to you happens again, you can break SO MUCH MORE! Soz @Sitting Duck 😁 On a budget get this piston and spring; https://www.ak2m4.co.uk/internal-parts/pistons/rocket-3-tooth-piston https://www.ak2m4.co.uk/internal-parts/springs/aols-aeg-spring-m100 If you want a stronger piston that is still a great fail safe, then get one of these; https://www.fire-support.co.uk/product/ics-reinforced-upgrade-pom-piston-set Link to post Share on other sites
Supporters Sitting Duck 3,394 Posted January 17 Supporters Share Posted January 17 @miserydrift has hit his daily post limit it seems so this is why he hasn't responded it seems @Davegolf - yes metal rack pistons give you weak point but the SHS 3 steel & 7 steel pistons are shit imho the plastic is softer not so durable like stock Cyma/JG 1 metal tooth pistons in fact SHS 3 or 7 tooth pistons are weaker than G&G stock pistons I've found the plastic teeth stripped quickly - way too quickly and at mid 20's so not PME plus SHS's - well the metal rack ones may bind in there so expect the 3/7 teeth ones too (no biggy but a bit of modding will fix) however I just think the SHS part metal rack pistons... well the metal teeth are fine it is the plastic teeth is just a bit DairyLea imho weaker than decent stock pistons like Cyma/JG as I said so the OP now might have an understanding on keeping the ROF down a bit so a metal rack will be fine & durable... AS LONG AS THEY DON'T GO NUTZ - which hopefully he understands it a bit better OP might grasp the fact there is no fail-safe or weak point to avoid risking PME if push came to shove I could send him some stock Cyma pistons (hardly been fired), if he was that worried but as long as he understands the limitations/rof stuff he should fine with a robust full metal rack yes maybe part metal rack - but nope not SHS 3 or 7 tooth rack (Sorry SHS but your plastic is way too weak/soft) people can argue or differ in their opinion on these pistons but had one fail very very quickly on me also - remove the 2nd tooth etc.. on a SHS part metal rack - see how easy it is to remove with a sharp knife cor - this is easy... yeah it fucking strips easy too in use then remove a tooth on a hard Cyma/JG piston - not quite so easy coz it's more durable material fucking shame coz SHS pistons are nice n light - just really don't think they are that durable tbh (sorry if people think otherwise - but I gathered up any I had and flogged them on fleabay years ago) Link to post Share on other sites
Davegolf 799 Posted January 17 Share Posted January 17 I completely agree, I don’t think they are THAT durable, but good enough for a stock ish 1J gun. Any POM half rack all day for me. Link to post Share on other sites
Supporters Adolf Hamster 3,753 Posted January 17 Supporters Share Posted January 17 kind of agree on shs's plastic, assuming it's the same as the bodies of their full rack pistons because that's what i'm normally looking at running. if the gun is put together right and not run too hard then either works, but plastic does offer a bit more insurance for the gears if you're worried about it being too fast. either way it's a pain in the ass to clean up when one goes Link to post Share on other sites
Supporters Sitting Duck 3,394 Posted January 17 Supporters Share Posted January 17 Seems like the hop might have caused a BB to jam than actual speed which resulted im PME piston shredding he can't post atm so is posting in updates bit maybe lips or hop on way too much - well what ever Another piston to be careful is the 3 & 7 tooth dark grey ones from TWG they are a bit shit also had one just rip the rip initial pickup tooth right out https://www.taiwangun.com/piston/reinforced-piston-with-seven-steel-teeth?from=listing&campaign-id=19 Hard as fuck - like nails that plastic, like brittle hard as fuck plastic had some 3 & 7 tooth versions... I think the pick up tooth is way too large/deep and kicks the sector as it returns had one of those just crack the pickup right out was a long time ago - but knowing what I know now I could carefully file the massive pickup down a smidge and keep checking shit in top half of box as I often do yet my gut feeling is just a tad ultra hard & brittle plastic/polymer but another piston I tried and thought nah fuck it I got a few pink OEM ACM 7 tooth pistons - they're fucking ace as well as some pink full metal rack pistons about 3 years ago from GF for a few quid - they were fucking awesome & didn't bind in boxes like SHS did wish I could find them but reckon they are long gone from production would be like finding a fixed stubby M4 stock - like rocking horse shit or hens teeth nah - tried 3 part metal/plastic pistons and only one of them was any good and that one is no longer in production it seems - just my luck so tend to stick with metal racks myself - but to each their own here are the OEM ACM pistons that I love... the 50/50 rack is at back - shiny surface but these are damn good pistons - that don't bind like SHS's need a bit of work/cleaning up but fits the bill when a SHS binds if anybody sees these around they are pretty good pistons imho (probably seen them in some of my build posts) I'll use a SHS metal rack in a G&G as it don't bind Try a Cyma metal rack in others but if the G&G is too tight, the Cyma is a tad loose (bit too much plat left/right & up/down as piston moves back/forth) Then one of these pistons are usually chosen as they are in between a tight SHS & sometimes smidge too loose Cyma yup they are/were damn good 'uns where as the SHS & TWG grey 50/50 pistons - not such a wise investment Something similar to those pink 50/50 pistons is this... https://www.taiwangun.com/piston/reinforced-piston-with-seven-steel-teeth-bw?from=listing&campaign-id=19 Often I didn't need them or out of stock to add to a previous order BUT if anybody is doing a TWG order at some point & might need a 50/50 piston well I reckon they could be worth a gamble on buying a couple of them That was about the only piston I saw like my 50/50 ones I've used/rated hasn't got the full complete intact rails but nigh on might need to check the initial pick up tooth isn't too high (in some boxes rubbing on sector's toothless area, very fine file) extra material on 2nd/3rd tooth surrounding area - bit of work removing chunky pickup tooth, won't need much to even partial correct AoE etc... (yes often shit needs a bit of tweaking, glue the rack etc...) if it is like my pink ones, they shouldn't bind in most boxes but not too much play/slack either - just the right fit to glide without binding End of the day, it's a case of checking & getting whatever shit you got to hand all operating smoothly & efficiently etc... Link to post Share on other sites
Supporters Adolf Hamster 3,753 Posted January 17 Supporters Share Posted January 17 ahh yes, see the status update. so my spring theory was wrong. you win this time duck Sitting Duck 1 Link to post Share on other sites
Supporters Sitting Duck 3,394 Posted January 17 Supporters Share Posted January 17 Didn't win anything - just guesswork but we've all broke shit lots of times in many different ways THIS is my favourite of favourite pic that sums up diagnosing shitty bastid toy gun issues.... poor OP won a fucked piston & lost his posting ability whilst having to wade through all my crap instead - ouch that's gotta hurt Davegolf and RonLancs 2 Link to post Share on other sites
Davegolf 799 Posted January 17 Share Posted January 17 Yes this is most common fail, basically pneumatic lock “Seems like the hop might have caused a BB to jam than actual speed which resulted im PME piston shredding” One of the reasons 6.00 / 6.01 barrels are daft too. Dirty jam. Sitting Duck 1 Link to post Share on other sites
Supporters Adolf Hamster 3,753 Posted January 17 Supporters Share Posted January 17 15 minutes ago, Sitting Duck said: Didn't win anything - just guesswork but we've all broke shit lots of times in many different ways THIS is my favourite of favourite pic that sums up diagnosing shitty bastid toy gun issues.... personally i prefer "the master has fucked up more times than the apprentice has even tried" 15 minutes ago, Sitting Duck said: poor OP won a fucked piston & lost his posting ability whilst having to wade through all my crap instead - ouch that's gotta hurt i still think one of these days we just need to go through your post history and stitch together a proper "how to gearbox" guide 8 minutes ago, Davegolf said: One of the reasons 6.00 / 6.01 barrels are daft too. Dirty jam. yeah, you do have to stay on top of cleaning with the tighter bores, but then regular cleaning is still the best cost/performance ratio "upgrade" for any gun. Sitting Duck 1 Link to post Share on other sites
Supporters Sitting Duck 3,394 Posted January 17 Supporters Share Posted January 17 Oh leave off - I'm still trying to figure that out myself Link to post Share on other sites
Supporters Adolf Hamster 3,753 Posted January 17 Supporters Share Posted January 17 Just now, Sitting Duck said: Oh leave off - I'm still trying to figure that out myself i know what you mean though, it's impossible to make the complete guide for everything because every part and every gun is subtly different, things change over different batches etc etc. Sitting Duck 1 Link to post Share on other sites
Davegolf 799 Posted January 17 Share Posted January 17 @Adolf Hamster no need, @Sitting Duck writes the guide every time he posts 😘 I love how every time the ‘I want to put a new spring in’ spirals into full blown custom box Sitting Duck and miserydrift 1 1 Link to post Share on other sites
Supporters Sitting Duck 3,394 Posted January 17 Supporters Share Posted January 17 Can't accuse me of composing very brief & vague posts just bored shitless & very very very sad miserydrift 1 Link to post Share on other sites
miserydrift 71 Posted January 17 Author Share Posted January 17 Thanks guys and yes it seems it was a jam thats caused it now to order the piston sitting duck mentioned and go from there,so hard not to strip the 516 for its piston but after chrono'ing it earlier i think i will leave that gun alone as its sitting around the 315fps and acurate as hell as managed to keep my groupings quite close now to get the 621 to be the same lol Link to post Share on other sites
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