Hi All,

Doing some maintenance on my USAT switchers, NW2 and S4, and noticed/observed a few strange things I could use clarification on. I founds Greg’s very helpful articles on fixing the cracked gears (all 4 on the NW-2 were toast) but a few cuts of brass tube later we are back in business. However once everything was lubed up, closed back up and put on the test rollers to checkout/do the final wheel cleaning, the motor blocks have a clicking/buzzing sound coming from them, mainly at low to moderate speeds.

On the NW-2, I saw the end motor block set screws were almost all the way backed out (like this from factory) and the plastic square the screw sits in was vibrating, causing the racket. I confirmed this by sticking a screwdriver against these set screws while on the test rollers running and it went away. On the S4 when flipped over, the set screws were pretty much all the way in (again like this from factory), with very little movement/vibration of the screw/plastic square, unless run at very slow speeds, then it sounds like an arcing/sparking motor, until you touch/hold the set screws. I did confirm the motor was not arcing

I disassembled each, re-lubed the gears, housings, contact points, the ends of each motor block where the screw hits the worm gear and re-assembled. Still has the same issue. Also an interesting note, the engines have a very distinctive “direction” the motor sounds better in. When in reverse for example, the gearbox and motors are pretty quite and have the typical USAT hum when running. Stop and flip to forward, and the gearbox is notably noisier and seems to run rougher. Also another note, both engines appear to have the “older” style wheels/axles and gears with the straight groove cuts in the axle going into the plastic gears as opposed to the new helical style I believe USAT uses now. The gears also have the slight slant to the teeth, which I believe is correct for these engines.

So with all that here are my questions:

1. How far should the set screws be tightened against the ends of the worm gears? Is there a magical “gap” setting like a spark plug that needs set?

2. Is the directional gearbox noise typical of the USAT engines (I.e. one direction is quitter/smoother than the other)? I have never noticed this on my bigger GP-30,GP-38 and GP-9 engines The Nw-2 and S4 engines are fairly new with little run time. I also used Greg’s article and confirmed all motors appear to be fine with no dead bearings/wobble of the motor, the plastic gears teeth also look fine as they have very little run time over the last few years.

3. Anything else to look for or to do to quite these engines down? I should note, I am running these overhead on 1x4 with no insulation. I understand the noise will be greater, but the clicking/arcing sounds is heard even when on the outdoor layout. Want to be sure I am not stripping out gears or have some sort of bigger issue looming.

Thanks All

-Chris