The rotary couplers were purchased from Sergent Engineering. The coupler is a non operating unit that is larger than the operating Sergent Engineering and Kadee #58 couplers. The coupler has no provision for being able to swing in a bend in the track. The instructions say it will handle a 22” radius. After staring at the car and new coupler a decision was made to use a combination of machining on each piece to mount the new coupler. This allows the use of the truck mount screw to pass though the coupler and mount to the car frame aligning one to the other. A small spot of CA at both ends secures the pocket to the car. The pin that secures the coupler to the pocket needs to be trimmed to clear the car frame during a 360 degree rotation.
The operating Sergent Engineering couplers may be able to be modified to operate in the pocket. Trimming the shank down and pouring a urethane casting around it to make the shank circular is the idea. The urethane sands easily and is very strong. A hole would be drilled through the top of the shank for a securing pin. The stock rotary unit has the pin sticking out one side of the shank and would keep any future alterations for allowing more swing in the couplers (altering the pocket hole to allow some swing). A small mold is being made to hold the trimmed shank of a Sergent coupler to pour a round shank in order to use them in the rotary pocket. This mod will give a true scale appearance to the rotary coupler.
Picture o576a.jpeg shows 2 Bowser cars; frame after machining and with the truck/coupler installed. Below is the stock rotary coupler and its modified version. Below that is the operating Sergent Engineering coupler.
Thanks for posting the picture if your modified Sergent bolster. I picked up 4 paks of these about a year ago and after seeing how you did your modifications I have installed the rotaries on 6 PPLX Bowser cars. Time to order enough to do the rest of the 60 car fleet. Now all I need is a good working dumper !!! Thanks again, ------- Ken McCorry