Bachmann 4-6-0 "Big Hauler" Overview: Bachmann has a very famous loco, called the "Big Hauler" (There is a special version called the "Anniversary Editon" or "Annie" that has had variations in detail, quality, etc. see under 5th Generation). It has been continually improved over the years, so it's common to try to identify the "generation" so as to know the "quality level" when buying a used one. 1st Generation: 1988-1990 The first generation was battery powered, had a simple remote control system, and had a small motor, plastic wheels. It had a multigear gearbox. The motor was 6 volts. You can turn the drivers by hand and the motor will turn. No worm, a right angle spur and crown drive Note--the controllers came in two frequencies--27 MHz and 49 MHz. If the loco number had a "7" in it anywhere (like, 7, or 27), it was 27 MHz. If it had a "9" anywhere (like, 9, or 49) it was 49 MHz. Early Big Hauler flanged wheels have a plastic hub which is driven on to the axle (and quartered). Note the big battery compartment in the chassis below: 2nd Generation: 1990-1994 The second generation used the same gear train, but had a 12v motor, and ran from track power. The motor block has a smooth bottom cover. It still used the 90 degree spur and crown drive. There were variations in the gear on the motor, the picture above shows a gear that is "cut" the length of the gear. The picture below not only shows a cracked gear, but note that the gear teeth do not extend the full length of the gear. 3rd Generation: 1994-1998 The third generation was also called the "Plus" model. It has a better motor (but a weak motor mount), better gears inside (idler and axle spur gears). The bottom cover is still smooth, but you cannot turn the wheels to turn the motor. this is because the drive used a worm gear. The motor mount would let the motor to move away from the cluster gear and strip it. People usually used a big ty-rap to hold the motor in place. The worm gear diameter is ~0.68" in diameter. In the picture below, notice that the "motor mount" ring has come loose from the motor. This helps cause problems with gear mesh. 4th Generation: 1998-1999 There is a large, wide hump centered between the read drivers on the bottom cover. The axle half with a square end which goes into a sound drum or drive gear. It may be that only this generation has this split axle. Sound drums split, gear hubs split, wheels came adrift. Same motor as before, just mounted to a metal channel. The worm gear was actually an assembly. The inner part attached to axle hub with 4 pins that was "heat riveted" to the gear. They did come apart, and there was no way to repair. The worm gear is 1.245" in diameter (the reason for the big hump). Notice the splits in the hub on both sides. When this happened, the motor and gear would move but not the loco. 5th Generation: 2000-2012 There is a 3/8" wide hump offset (not centered) between between the rear drivers and a plastic lubrication plug the size of a dime to the rear of the hump. The fifth and sixth gen wheels mount on a solid axle with plastic pieces in and around the hub. The drivers were attached to the axles with screws. Bachmann claimed Delrin is no longer being manufactured, so wheel bushings are now made of Celcon. Lots of rotational play in the wheel and axle assembly. The picture below shows a generation 5 BH, but with plastic side rods. Some people believe all generation 5 locos have metal siderods, but this shows it's not true. Below you see a generation 5 gearbox. Notice the screws to hold the wheels on. Enter the Anniversary Edition ("Annie") Anniversary is also Version 5 chassis...there were some Costco/Sam's that were contracted to be a price point (we need to talk) and at one point Kader dragged out the old molds to satisfy that. In the photo, see the small rivets on the smokebox? Not pie plates? Anniversary. Metal rods with oil caps. Anniversary. Crosshead guides with oilers. Smokebox support rods screwed to pilot beam. Metal piping (and cooling coil on outside of air tank). Electrical conduit and junction box. All specific to "Anniversary" design. Notice the top of the steam dome is gone, with whistle and pop valves. 6th Generation: 2012-present All metal gearbox. Normally the Anniversary models were the same, except had metal side rods,improved pilot truck attachment (gen 6), The typical Mabuchi motor used was 1.08" in diameter, housing legth (w/o bushings) 1.49", 1.71 wth the bushings. Short shaft versions were about .26", the worm was .610" in length, with 8 lands series , on a series 3, there were 6 lands in the same length On the chassis with the gears retained by pins pressed through the chassis, only one end is knurled, so when pulling apart, only push the pin out a bit, and see if it's the knurled end... if not, push it out the other way, so as not to force the knurling through the gear.