Thompson Upgrade Guide

Hi guys thought i would do a litte upgrade guide as it was time to crack open my gearbox and give some of the hard worked parts there well deserved retirement. After an approx 100,000k rounds going through her with nothing changed apart from a new tight barrel she has done well. As always i have taken advice and had help in doing this from my good friend Nathan.

The Plan

To have my AEG turn back to the true work horse. She is used about 12-14 times a year and as i attend my sites with Highcaps. So she will have a fair few rounds going through her. During a Charity CQB game at Xsite (which was excellent) in Decemember, the weather showed me how much AEGs suffered from the temperature. So i wanted to make a gun which still performed well, even in the worse temperatures. After a lengthy discussion with Nathan i didn't want a quick fix i wanted something to go in there and would not need touching again for a long time. We decided using Prometheus parts as these were made to the highest tolerences and had certain parts which were very stong as they were sintered. (gears as example) So with that in mind the parts ...

Parts List

2 New Springs - I like Madbull springs because from personal experience they seem to hold there FPS the longest. What i mean by this is that a gun sometimes will be "hot" until the spring wears in slightly bringing the FPS down. With madbull i find that the drop is minimal and consitancy it will chuck out even after 10.000's of rounds have gone through it will be amazing. They are less "pokey" then other brands so i have brought an M110 and a M120. (mainly just to test the FPS difference)

Prometheus Cylinder Head Version 6 - simply upgrade to get a better air seal. (improves consitancy and FPS)

Prometheus Normal Torque Gears Version 7 - Ok quite a bit to say about these.

The Thompson is a version 6 gearbox and will take Version 2, 3 and 7 Gears for definite. However! Not all brands will fit. I would be happy to have TM, Classic Army (they do 2-3 P90's which use version 6 gearboxes so must of got it right about now!) or as always the expensive Prometheus. (I will be happy to add any furthur brands to this list if people have experience using them). Using other brands like G&P, Systema, Element, ETC may result in binding issuies (plus other problems) and as gears are generally the most expenisve thing in a gun it can be a costly mistake. Prometheus gears are sintered, so they are the stongest gears you can buy and as a result should last the longest.

So why Version 7? This was because of 2 reasons. I wanted to see how an "M14" set of gears worked in a Tommy, and secondly because they were cheaper! Also i chose normal gears as i did not want to go over 350 FPS. So i had no need for double torque or triple torque gears. The rate of fire i think is good enough with a 8.4v or 9.6v battery so did not want to put "high speed gears" in her as these are built not to last but to chuck BB's out as quick as possible.

Systema Air Nozzle - Ordered this as the Prometheus version was out of stock. Systema make some good parts and i felt this was the 2nd best option to use for the air nozzle. May exchange it at a later date but works fine atm.

Prometheus Stop Latch Version 6 - This helps the gears from spinning backwards after the last shot has been fired. Helping reduce wear on the gears and damage to the gun. Also i find because of the number of latches on the prometheus gears (5) you get a slightly better trigger responce.

Prometheus Spring Guide Version 6 & 7 - The version 6 and 7 gearboxs use the same spring guide so this is the one you want. It has bearings which puts the spring under less stress and increase the FPS. WARNING Although i am very happy with this being in my gun if you have done the "bolt mod" you will not be able to use it anymore as there is a screw holding the spring guide together. (because of the bearings) I have not attempted to modify this yet, but may do in the future. (if anyone has done please let me know and i can add that information)

Prometheus Hard Piston - Very stong piston, to go with the strong gears. This one should fit 90% of AEG's. Do not buy the M14 Piston as the M14 gearbox uses a different piston.

Prometheus Piston Head - Will again fit most AEG's. Just find one which says will fit a "TM"

Not Pictured.

Prometheus Sintered Bushing for Version 6 - You must buy version 6 specific, others will not fit at all! Another sintered part so i know it will last a long time.

Upgraded Cylinder - already had one installed possibly Systema or Hurricane. Improves Air seal and a slight FPS increase.

Guarder Tappet Plate - version 6 ones seem to break every now and again, so brought an upgraded one to work in conjuction with the other upgrades.

To Work

The first thing you notice is the gearbox will be quite dirty and or full of grease depending on if your gun is TM, China or if someone else has already cracked it open. So remove all your parts and give it a good clean. The bushings have have already been tapped in. Please note this current picture will take the version 2 and 3 gears.

How ever one quick flip of the oval bushing and you can now fit your version 7 gears.

The Gears will go in as picutred below. Please note that all gearboxes will need to have there gears shimmed. This will stop binding gears and additional wear on the gears too. This is the most painfull process. I will not go into great length how to do this. A simple google for "airsoft shims" will bring up loads of you tube videos. At this point as well we put a small amount of gear grease on each tooth ( i mean small!) so each tooth starts of "wet". Please also note that a small amount of grease is added to the bushings.

Once we had the gearbox open and closed about 30 times to make sure the gears were not binding and were all hapily seated we then continued with the rest of the gun. We made the piston and piston head. These parts are quite self explanatory. (dont forget to add some grease to the inside of the o ring) Many people use different glues and methods we just used a little red lock tite to secure it. Picture of assembled piston and picture of the screw locktited in the bottom.

Some grease was then added to the "tracks" of the piston and inside of the cylinder. We have also attached the head to the cylinder in the next photo.

Finally its just a case of attaching the spring to the spring guide (the most coils of the spring should be attached to the spring guide end) adding the tappet plate (as shown in the picture) and adding the anti reversal latch (pictured bottom right of gears). Also note that the anti reversal latch may need to be shimmed. It comes with its own shims, although when added them the gears started to bind so in our build we did not use them.

Test Firing

Well the biggest anti climax was once we had locked and loaded we didnt have a fully charged battery. We managed to let off about 20 rounds until it died, and it sounded meaty! When i meet with Nathan again i will make sure my bat is charged and the Chrono has a new pair of batterys installed. I am hoping that the gun is just over 350 so it will be a good excuse to put the old spring guide in so i can have the blow back mod working again.

Airsoft Knowledge

I wouldn't of been happy doing this alone so i was glad to have someone with me who knew what they were doing. I have also been a fan of all the Prometheus parts in the past but it does not mean that you have to be. If you are someone who has not had alot of experiecnce with gear boxes then buying "cheaper alternatives" could be better than breaking £100's of expensive parts. If something goes wrong.

I hope you have found some usefull information here. I apoligise for any spelling mistakes or typos as it is getting a bit late.