Thompson Problem

[redvonhammer]

Hi all!


Airsoft season is coming up, and I figured I`d better prepare my airsofts.

I tested my Cyma Thompson recently, but something weird is going on. When I fire it, sometimes the bb`s just roll out of the barrel, and other times they fly out and then go up (As I would normally expect.) And next bb will be going out with no hopup effect, and another with an effect in between... And sometimes not even a single bb comes out of the barrel, though the mag is full, could be one mag which springs I forgot to oil. But shouldnt make gun shoot this weird.

Then I decided to shoot at a cardboard box, and dang if not a single bb successfully penetrated even one side of it :S

I have done some mag insert/extract practice with it, but I never slammed them home-free (Which is a no-no from what I read.) Yet I am seemingly rewarded with what I thought was a great gun and good backup for my M1, to turn out non-functionable at this point.

I opened up the gearbox, did the usual grease maintenance (And took myself 2 hours in the process, just to make sure everything is smooth.) As well as checking if the inner barrel might be pointing at the bottom or top inner edge of the end of the outter barrel (Anyone who as experienced bb`s going up and down for each shot, would know what I am talking about.) But thus far, despite taking any precaution that I can think of, nothing good is coming out of it (Though it is not getting worse either.)

Should anyone have a suggestion please do not hesitate to post!



Happy hunting all!

RvH

[biged]

Sounds like your hopup is over adjusted. The shot will fly too far up or not leave the barrel because of the hopup preventing it from leaving. Which will cause a bb to fart-out like a pool-ball effect inside the barrel.

Turn the hopup down first, see if the feed improves. If it does not, inspect the hopup itself. You may have a torn hopup bucking which should be replaced.

///ed///

[kalbs]

There could be a few problems but it sounds like either you tappet plate is not set properly on the nozzel or it's broken.

[schmitty]

Sounds to me like tappet plate nozzle related problem, The tappet plate is pulled forward by a spring and pulled back by a cam on the final gear. If the tappet plate isn't greased or is dirty or possibly has something blocking its path (such as little bits of the pistons teeth that sometimes come off). It will not spring all the way forward consistantly resulting in no seal between gearbox and barrel and inconsistant and generally low FPS.

To test: remove upper reciever, Fire gearbox until it stops with the nozzle all the way forward. Push on the nozzle with your finger, It should spring back forward instantly and smoothly, If you feel any friction at all something is wrong.

The remedy: Remove tappet plate, Sand edges smooth. Clean track in gearbox, Make sure nozzle moves smoothly on cyl head. Grease everything, Re-install. Test again.

This is only one possible cause of your trouble. But it's where I would start. Also check Ed's suggestion of simply too much hop up.

Schmitty

[2ndranger]

Or when in doubt send it off to Biged...

Franz

[redvonhammer]

Hi again

Took me some time to report back as I`ve had a naughty Trojan of the name Vundo on my computer, rendering all Internet Browsers useless, now that that`s removed, I can get on with this again.

I dismantled the gearbox and checked the tappet-plate, fortunately, no pieces are broken off, and gearbox is well-greased. In short, I fail to observe any kind of visible technical failure. I also took out the barrel and hop up and looked straight into it for good measure, but it`s nice and straight.


Sending the Thompson to the states, or, anywhere for that matter, for repair and back would be worth its retail price 2 times (As we dont know whats wrong, the entire thing must be checked, thusforth cannot afford to overlook one bit of it.) But I appreciate your concern In any case, if I can`t fix it or at the very least locate the problem, I`m sure as hell not worthy to be owning the very same airsoft I hope to atleast be able to skirmish with. (Thats right, I havent skirmished with the Thompson even once.)

So if anyone has a bright idea here, I`m all ears!

RvH

[HellRazor]

Have you checked your piston seal? I've had this cause poor FPS before, just because its lubed does not equal a seal. This can cause the exact issues your reporting. If it is not that, I've seen broken nozzles, cracked hop ups and torn buckings all cause the same, but honestly in the, oh 2 dozen weapons I've repaired with this issue its generally because the seal was lost on the piston.

[Red Von Hammer]

Hi again

Have to write with a guest pass this time.. Currently using a Vista laptop with a complete lack of stability..


Every part, to my best knowledge (And some healthy folk wits.) Looks okay, no disturbing damage or bends, cracks, of any kind. (And I reagard myself pretty throughout as for airsofts and their internals. Once, my KWA/KSC Glock17 got a blown piston seal because I maintained the gun TOO much.) And my Thompson`s seals are all nice and ok. no leaks or such either. It`s just that whenever I attempt to fire it, BB`s, as mentioned, either rolls out of the barrel, or comes out with no hop-up effect, or drop after just a few metres. I would have thought that might mean that the gearbox is vibrating too much so the bb`s first hits the edge of the chamber before then gliding into the barrel or something?

Grim tidings indeed..


Sincerely Yours
Red Von Hammer

[supernube]

Replace your hop-up bucking. There could be a tear or leak in the rubber. CYMA is notorious for their crappy buckings.

[Red Von Hammer]

Indeed this seems to be the case.


Most of all this reminds me of hop-up in every single way. I`ve slammed the mags (Not hard, but still, slammed.) home sometimes. And the bbs roll out the barrel or go far or go short, my buddys Tokyo Marui Desert Eagle had the exact same prob, and thats a gas gun. I merely adjusted the hop up to its correct settings. No longer a prob. Ill switch the hop up either case, because the old one will go anyways.


Does anyone happen to have a takedown manual on the hopup assembly btw?


Sincerely Yours

Red Von Hammer

[redvonhammer]

Situation update:

The problem was that, last time I opened the gearbox, I forgot to check that the tappet plate was fastened to the nozzle.. Problem solved, my mistake, and I am sorry for bothering you all with my incompetence.

At least now I have a complete V.6 Gearbox check-list in my head, thus I bow my head to the greater heads on this forum (Schmitty`s hint gave me a point-pin as to what the problem could be, that is, after checking everything 3 times to be sure I had it all right... )

That said, I was wondering about 4 things, now that I have a thread about this, if I may that is. This would help me alot.

1: If I was to put in a better battery (A buddy of mine has a 9.6 1200 mah battery which brings his Thompson`s ROF sky high.) Do you think my Systema Short Turbo motor would work in the Thompson then? Last time I tried, it refused to spin the gears all the way around, and other times it does spin them around for about 3-4 revolutions (3-4 shots fired.) possibly because of weak battery?

2: I am thinking about installing a weaker spring (For less wear on engine and gears, and possibly contribute for better performance as for the Turbo motor. As well as allowing me to use the Thompson at all distances.) But I am unsure exactly what kind of spring I should look for, does anyone have experience on this field?

3: I am also thinking about installing a precision barrel, so that I may uphold accuracy even though I am sacrificing power, but I am unsure as to how disassembly of the hop-up is done correctly, as my Thompson did not come with a disassembly manual. I have searched for a manual online, both TM and Cyma, but have yet to succeed finding it, if anyone should happen to enlighten me, I would be most grateful.

4th and last: If I wanted a carbon piston (For slightly less wear on flywheel and nozzle due to the higher ROF caused by the upgrades and changes mentioned above.) Should I just look for a V.6 gearbox Carbon Piston or is there more to this?


This is all I need to know to get efficient performance out of my Thompson (Which will soon, hopefully, be looking like a M1928.) as well as further helping me immensely much in my pursue of knowing more about aeg internals.

Btw, ordered a Phoenix 1928 front kit from gunnerairsoft, will probably get it within the week, if anyone wants pictures I`ll put them up.

Sincerely Yours

Red Von Hammer