Airsoft Action 07 - Mar 2012 - Page 64

Identifying the gearbox Identifying problems ■ AEG is cycling but air nozzle is not moving? The tappet plate is probably broken. ■ Gears are moving, along with the tappet plate and air nozzle, but no ‘pop’ from the piston? The piston is probably broken. ■ Grinding sounds from the gearbox? Check for incorrect motor height, poor shimming, worn gears or possibly damaged bushings. ■ AEG still functioning but with a drastic drop in velocity? The spring may have snapped (an exceptionally rare problem). ■ AEG has been working fine but suddenly stops and the motor will not cycle, and you know that your battery is still charged? Then the motor has probably burnt out. ■ Piston stopped moving or grouping and range of BBs has become erratic? The O-ring on the piston is probably broken. ■ Barrel jammed, and not due to a dirty barrel or cheap BBs? The hop rubber may have split, your hop setting may be too high, or your hop unit has cracked (the latter is rare and only found with plastic hop units). Version 1: Tokyo Marui’s first gearbox is found only in the Famas. 064 March 2012 There are several different variants of gearbox, known as versions. These range from V1 to V8, with some being much less common than others. Each version has parts that are specific to it, and are not interchangeable between versions. These include: spring guides, tappet plates, air nozzles, trigger mechanisms and motors. The most common are V2 and V3 gearboxes. The easiest way to tell them apart is by looking at the top of the gearbox; a V3 has a metal slide that holds both sides of the gearbox together while a V2 relies on screws to do the same job. If you’re not sure which version you have, compare the shape to those shown on these pages. Within the gearbox, and attached to it, you will find the following parts: motor, anti-reversal latch, bevel gear, spur gear, sector gear, spring guide, spring, piston (with attached head), cylinder (with attached head), tappet plate and spring, air nozzle, trigger mechanism, bushings (metal or plastic) and shims. Gearbox maintenance essentials Make sure you are wearing eye protection before splitting the gearbox to avoid damage caused by any small parts ejecting at speed. It is also important to have all of the necessary tools to hand. When splitting the casing you need to ensure that the spring does not eject from the gearbox as it may snap the spring guide. The risk of this happening in future can be reduced by replacing the stock plastic spring guide with a metal version. It is important to keep the moving parts well-greased but avoid over greasing, as it leads to them moving slower, jamming and draining battery power. The gears should be correctly shimmed as a lack of shims can lead to gear and piston wear and the tappet plate being impeded. Use a grease of light viscosity (one which appears clear or translucent white). If using heavy based grease, which is usually black or dark brown, apply it sparingly. While you have the gearbox apart you should check for wear on gears and remove any metal filings. Version 2: One of the most common gearbox types. Several companies have redesigned and improved upon it, but there are essentially three variants: windowed, non-windowed and ICS. Shown here is the windowed version (note small ‘window’ to rear of gearbox) usually found in Armalite rifles (which cannot take a non-windowed type as it doesn’t allow for the body tabs to pass over the gearbox. The non-windowed type is found in non-Armalites. V2 used in: Armalites (CA, TM, G&G, G&P, AK); MP5 (CA, TM, G&G, ICS); G3 (CA, TM); M249 (G&P) Do not force the parts if you encounter resistance when putting the gearbox back together. The parts may not be correctly placed and continuing to force them could cause unnecessary damage. If you lack experience in opening gearboxes always seek advice from your local gun-tech, or check out some of the millions of videos that deal with the subject on the internet. Version 3: Favoured for its reliability and the abundance of aftermarket parts available. Look for the retainer plate on the top of the gearbox (instead of screws, as used in V2). Also has a thicker shell. Note: though SIG gearboxes can take V3 parts they are not normal V3 boxes – it doesn’t have a motor cage, and features a unique fire selector. V3 used in: AK47 (GG, ICS, TM, CA); AK74 (GG, ICS, TM, CA); UMP (GG); Steyr Aug (TM, CA); MP5k (TM); G36 (TM CA)