By Brian Scace
I’m a firm believer in one all-truism when it comes to locomotives. Whether you’re running conventional cab-control or command control, an O scale locomotive drive should have impeccable mechanical and electrical performance properties before any electronics are added. In spite of the current wisdom of the ready-to-run marketplace, electronics such as DCC are not a satisfactory patch for the less-than-stellar mechanical performance inherent in the current design of diesel drive-trains.
This brings me to the time-honored horizontal double-reduction drive we fondly remember, specifically the Weaver chain-drive. For those who may not know, this drive appears in quite a few different diesel models, such as the older Weaver plastic offerings, P&D’s beautiful F-unit line and a drive made for the Red Caboose Geep, and the various Alco and Baldwin switchers imported by Carworks. However, nice as they are in stock form, the starting performance still leaves room for improvement, hence this little piece of wisdom.
Recently, I picked up a Carworks Alco S2 from a gent who turned me on to Sterling Instrument. These folks make sprocket drives for instrumentation and small mechanical devices; they’re not a hobby manufacturer at all. In their line are a variety of sprockets just perfect for tweaking up the Weaver chain drives. In the photo, you’ll see my application. Look at the difference between the little stock 12-tooth lower sprocket and that big beautiful Sterling acetal resin 18-tooth sprocket (Part #A 6M 7-121806). These have a 0.1227 pitch and a shaft diameter of 0.188″. I just popped off the stock 12-tooth sprocket at the bottom of the tower and pressed on a 18-tooth sprocket. Simple. Make sure you line up the upper and lower sprockets nicely and shave the hub-face of the new one back a bit to clear the tube/half-shaft arrangement in the truck. Add three bars worth of Sterling’s plastic chain (Part #A 6M 7-12, it snaps right in place on the Weaver chain and is a matched replacement), and re-assemble the drive. I’ve done this conversion on Weaver, Carworks, and various P&D Diesels, and find the resulting switching/starting performance on par with any of the custom drives I own. The hour spent swapping sprockets yields wonderful low-end performance. The Alco High-Hoods on my railroad can now slowly push a car, knuckle-to-knuckle, without even opening up the couplers! It’s what O Scale is all about.
Sterling has sprockets ranging from 10-20 teeth with shaft diameters of 0.125″, 0.188″, and 0.250″, all matching in pitch to the Weaver chain, so the options for re-gearing to suit are myriad. The cost of my project was a tad over a buck a sprocket, and an additional pittance for the chain (about $8.50 per foot). They have a web-based catalogue and ordering site. A quick check on your part might also discover that the All- Nation, Electric Shop, and NJ/CB chain drives might use either the same components or something else in Sterling’s arsenal. The play-value possibilities are just endless. Sterling’s address is: Sterling Instrument/Stock Drive Products, 2101 Jerico Tpke., Box 5416, New Hyde Park, NY 11040 Phone: 516-328-3300 [www.sdp-si.com].