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Shimming?


Snipin_Kyle

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If the gears aren't properly shimmed a lot of bad stuff can happen. For starters you need to purchase a shim set, and then completely rip apart the gearbox. Every single component needs removed to shim properly, this means piston, cylinder, trigger, all wiring, tappet plate, selector plate, cut-off lever, gears, etc. The only things that should stay in the shell are the bushings/bearings. Start with the spur gear, and get it up off the bottom of the shell with a medium shim. Then grab the sector and shim it such that only the teeth mesh with the spur, make sure the faces of the gears never touch, but don't shim it high otherwise it will bind the tappet plate. Then throw a medium on the tops of each gear, place the other shell half back on top, and replace all the screws and fully torque them down. Reach your finger inside and spin the gears, and use a small pick to push the gears side to side within the bushings/bearings. If they move side to side, shim the tops of the two gears more. If they bind up and don't spin freely, remove shims from the tops of the gears and shim it less. Repeat until the gears have virtually no side to side play and spin freely with minimal noise. If you reach your finger in through the cylinder opening in the shell, grab the sector gear, and spin it really hard, optimal shim jobs will allow the sector to rotate at minimum 4-5 full revolutions before slowing down or stopping. Once these two gears are good, work on your bevel gear, repeating this process.

 

Important things:

- You MUST FULLY tighten the screws for tests. It torques the gearbox together correctly for operational conditions. If you don't do this then you are liable to over or under shim the gearbox, which is detrimental in both cases, and sticks you back at square one. Simply holding the gearbox together by hand for inspection will not give you the proper answer.

- Don't try to do all three gears at once. Do the sector and spur combo first, then focus on your bevel. This insures proper placement of the gears and prevents face to face contact

- The bevel gears need to be shimmed high or in the middle. If you shim it low, the motor pinion will never make good, full contact, and your pinion will shred in short order. Try to keep it centralized.

- If you don't first remove everything from the shell, the tasked is made further difficult and the results may not be correct.

- Do not assume that the shims that come with the gearbox are enough to redo the gearbox. You need a complete new set with three different sizes of varying thicknesses to properly achieve the goal

- Once shimmed, put a dollop of grease on each end post of the gears. This ensure the shims that you placed on will not fall off and this cycle repeated.

- Since the gearbox is open, check air seals, inspect electrical connections, and clean out all the gunk and crappy Chinese grease. Relube with white lithium on all mechanical interfaces and silicone based grease on all air seal components (not spray, never silicone spray).

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Civey is right. I am currently based in Daytona Beach finishing up my degree here in the next 2-3 weeks. You can ship it down, but USPS gets pricey for shipping something that size all the way down here.

 

Go check out the pinned Recognized Community Techs topic listed right below this one. That's a list of everyone on this forum who is a gun tech and who can do the work that wont require shipping long distance to do. Everyone on that list is a tried and true, proven tech that is recognized by the community. Any one of those individuals will be able to do this for you.

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