PBL K-27 K-28 Driveline Upgrade

The 2003 runs brought in by PBL of various K-27's and K-28's are phenomenal models, strongly built and with beautiful detailing. The mechanisms on both my K-27 (D&RGW #456) and K-28 (D&RGW #478) were wonderfully smooth, and free of any hitches or binds. However, I (and another friend who had also bought a K-28) felt that there was an increased level of drive train noise compared to the previous runs of K-series models and we could initially see no reason why: the motor was the same dependable Canon EN-22 flat can, and the gearbox was a Boo-Rim clone of the SHS gearbox that has appeared in every K-series model since the first run K-36's. What was different was the connection between the motor and the gearbox: instead of the double universal joints connected by a sleeved tubing, there was a small flywheel mounted on the motor with an off-center pin that engaged a slot in a large shouldered plastic bushing that was mounted on the worm gear shaft of the gearbox, as shown below:

Now what follows is my assessment only of what the potential problem is. If you are satisfied with how your particular model(s) runs, then you need not read any further! I believe that the off-center pin combined with the increased mass due to the flywheel promotes increased noise from the motor, possibly due to increased lateral forces against the shaft bearings - all of which results in a significantly higher vibration level in the Boo Rim drive train - and which seems to in turn manifest itself in noise: growling, humming, or whatever. So I elected to remove both the flywheel and the shouldered bushing and substitute components from a NWSL 2.0mm Universal Coupler Set (part #489-6). Note that there are enough pieces to do TWO complete locomotives from one package!

Start by removing the gearbox and motor assembly from the locomotive chassis by unscrewing the gearbox axle gear cover plate and removing the torque arm mounting screw underneath the motor. On the K-28, it is easier to access the latter if you remove the trailing truck as well. Once this assembly is removed, remove the two screws underneath the torque arm that secure the motor mount and motor assembly to the torque arm. Now you can unscrew the side of the gearbox casing, and then lift out the worm gear. Make sure that you place the end bushing and spacer washers from the end of the worm gear shaft safely to the side so that they don't go astray. I removed the plastic shouldered bushing by using a NWSL The Puller II (part #55-4) which was likely overkill...you can pretty well just pull this off! Once completed, put the spacer washers and end bushings back on the worm gear shaft, place it in the gearbox, and reassemble it.

Removing the flywheel from the motor is a bit more of a challenge, as there is very little space between the back of the flywheel and the front of the motor mount. What I did was as follows: I (gently) placed the motor in a vise, and then with two flat-bladed screw drivers located at 3:00 and 9:00 (i.e. 180 degrees to each other), gently pried up on the flywheel. By doing this, I was able to move it just enough so that I could slide in one of the plates with the v-shaped slot in it from the NWSL The Puller II. I then started gently tapping the motor shaft - careful here, as you do NOT want to put a bend in it - until the end was almost flush with the outside of the flywheel, and then proceeded to use the NWSL tool to complete the balance of the extraction.

Now reattach the motor mount and motor assembly to the torque arm. You will note that the motor shaft and worm gear shaft almost meet. Take out two of the universal joint set's plastic cups and one of the plastic drive shafts, and note the length of this assembly. You need to trim a bit off of both the motor shaft and the worm gear shaft so that the shafts do not protrude into the open area of the cups and press against the drive shaft. Also note that the drive shaft should have a little bit of end-to-end free play, rather than be bottomed out in the universal joint cups, as in the following picture: