04/05/03 rev 01/16/07
We have invested much time and effort into our Bachmann Shays only to find mechanical problems continuing to plague us. We learned about some of them and described fixes on our previous page but the saga continues...
Last February (2003), son Randy, CEO of the Sawtooth Meadows Line (SML) called our Teton Short Line (TSL) Engineering Dept asking for assistance with Shay mechanical problems. SML Shay #5 died last fall as it brought down the last load of virgin timber. While overhauling it for this upcoming season the SML found another split axle gear. Usually not a big deal as we have had to fix several already. The bad news was that the broken axle gear jammed up the works resulting in a stripped plastic helix gear in the worm drive set. Bachmann reports "no parts are available and we have 30 Shays in the shop awaiting parts" The operating season is fast approaching and there is lots of timber to bring down. HELP!
The logging season starts earlier on the SML so we robbed essential parts from the TSL #2 to get the SML in operation. Our nepotism agreement between the SML & TSL railroads demands such cooperation and we had several more weeks before the TSL Spotted Owl Timber Co. could get into the woods.
With no parts available we had to take a fresh look at things. All eight of the 22 tooth axle gears on the two Shays had failed or been beefed up to prevent failure and now we feared we were embarking on another series of failures that we couldn't fix without replacement because the plastic helix gear was devoid of teeth. It's time to look at the whole drive train. Good engineering would insure that a drive train has a "weak link" that lets go when overloaded but is easily repaired. A slip clutch or shear pin comes to mind but then I fell back on my experience with motorcycles and there was the answer- A chain drive! I've repaired them on a steep mountain-side trail. Beats the heck out of stripping the teeth from a transmission gear.
During the research part of this project, I found a suitable replacement gear for the failure prone 22 tooth, 32 pitch axle gear that we previously beefed up with wire and epoxy. Lets start there and maybe you won't have to go all the way like I did.
Go to SERV-O-LINK Corp and find a delrin gear GC224. It's bored for a friction fit on a 1/4" shaft. The Bachman axle is 6mm (.236") and knurled where the gear rides. The knurling brings it up to about .243" and a wrap of .003" brass (K&S #727) makes a nice fit.
OK, you've got that problem put to bed, but as you dissassembled the truck, some plastic spacing washers between the wheel and bearing disintegrated. They meaured about .083" thick with a bore of 5mm and a diameter of 7/16" No sweat- just make a batch from Evergreen styrene sheet. I used a .060 and .020 sheet 'cause I had them. Mark off 1/2" squares, drill them .093", #10 bit, scribe and snap them, then stack the little square donuts on a 10/32 bolt a tighten down with a nut. Chuck the bolt in your drill and file into a proper donut shape.
The plastic insulating bushings in the wheel also disintegrated as you removed the wheel. Save the part in the wheel with some acc cement and then use one of new spacers on the outside of the wheel. Perhaps you have already saved this bushing using the technique I described on the previous page. If not, you'll need to find or make a metal washer and use it between the screw head and the new styrene washer.
Oh darn- The helix gear is stripped- now what? The going gets a little tougher but we can handle it. Time to scrap everything between the motor shaft and the loco axle and go to a chain drive. Start with a complete dissasembly of the power truck. I suggest you check out the procedure at George Scheyers site along with many other Shay tips. I found it less likely to break plastic if you remove the four tiny screws and dissassemble the brake beam assembly instead of trying to remove it intact. In that case there is no need to remove the drive shaft.
Two pins near the top ends will have to be pressed out to get to the inner works. Look for knurls on one end and push on the other end.
The new steel worm and brass helical gears come from NorthWest Short Line, (NWSL). They have an extensive line of 72 dp gears intended for smaller locos but I reasoned that using four sets, two on each truck distributes the work and forces and they just might do the job in G gauge. We'll see. I was unsuccessful at finding bigger, i.e. lower dp values like 24 or 32 in the ratio and other parameteres that we needed. The Bachmann Shay starts out with a worm gear reduction of 22/1 and then a spur gear reduction of 22/10 for a total of about 48/1. I selected a 24/1 worm set and a 16/8 sprocket set for a total of 48/1.
Serv-o-link has the slickest (pun intended) chain and sprocket system. The tiny delrin chain is about 1/8" pitch and about 5/32" wide. The specs look ideal for our needs. The original gearing resulted in 1/2.2 ratio. I found 8 and 16 tooth sprockets that fit and resulted in 1/2.0, close enough. The 8 tooth sprocket, #S082, is a friction fit on a 1/8" shaft, the same as our new brass helix gear. The 1/4"-16 tooth axle sprocket, #S164 will need a shim as we did with the delrin gear earlier or you can buy the 3/16", #S163 and bore it 15/64 (.234") as I did. This, however requires a lathe or drill press to keep it accurate. They accidently mixed two 1/4" size in with the order of ten 3/16". Check your supplies before tearing your Shay apart!
I later learned that Grandt Line carries delrin chain/sprocket pieces and I suspect they may be the same thing. The item price is about four times as great but then you don't have to pay the minimum order price of $30. I chose to lay in an inventory for other projects to fill out the order. In any case you do need the technical specs from Serv-o-link.
Compare the old gears (magenta) and the new (cyan) in my sketch/notes below. The middle 16 tooth gear and shaft is discarded as is the old plastic helix and 10 tooth plastic gear and shaft at the top.
The new NWSL 72dp worm gear with a 3/32" bore size slips onto the motor shaft and is soldered in place. The next problem we face is moving the helix shaft because the new all metal worm gear set is more compact. I determined that it would have to be moved .120" closer. I partially tapped the old helix shaft holes in the frame for a 6/32 jam fit, i.e run your tap only part way, then turn in a brass bolt with some ACC cement on it until it binds up. Cut it off and file smooth. The brass, unlike steel, is soft enough to not force your drill out of line when you make the new holes. Mark and drill 3/32" (.093") holes for the new music wire shafts. The old hole was .120" and you've got to move the center about .120" toward the motor shaft.
I'm better at electronics than machining and I didn't get it just right so I cheated. I overdrilled, and filed a bit too, the hole cutting into the brass plug and soldered a 1/8"od-3/32"id piece of brass tube to precision locate the helix shaft for full gear mesh. The pot metal frame won't take solder but the brass plug will and thats quite enough. You guys with only one thumb per hand would probably do better.
The brass helix gear is assembled with the delrin 8 tooth sprocket on a piece of K&S 1/8"od brass tube that fits and spins nicely on the 3/32" music wire shaft. Just solder it in place. The delrin 8 tooth sprocket is then pressed on. I added a small felt washer as an oil wick and a pair of 3/32" washers on the ends. Don't forget the gear grease!
Each end of the truck will need about 3 inches of chain and of course chain drives need adjustment but there isn't any so we'll just have to accept a little slop. The chain is spec'ed to work up to 2 pounds tension and fail at 7 pounds and I expected this to be the weak link. - WRONG
I put the power to it, watching the ammeter and gradually binding up one axle. The motor current was approaching the locked rotor value when the 8 tooth sprocket started to slip. The other axle behaved the same. If I bind up both axles, the motor stalls. Should a single axle bind up, it's likely the delrin sprocket would slip and be damaged. Well, if that happened, they are cheap and available in the US so you don't have to wait for a slow boat from China. Our electronic drive system with current limiting won't let this happen.
It seems to work OK, and we have enough parts left over to keep the SML Shay running for a while. In fact we have already replaced those %$#@& splitting axle gears with the new delrin ones. Perhaps that fix alone will preserve the original drive train.
On the TSL, The Spotted Owl Lumber Co. is in business for another season.
Will I fix yours? Let's see now- I'm sixty-eight and have about thirty-five man-years of TSL projects pending. Might be some delay. On the other hand, for $60/hour including breaks, naps, meals etal, I might consider it. You'd get a good job- I promise to work slow and methodical-GRIN
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