Putting a Branchlines Gearbox & Mashima

Motor into a Bachmann Std 5

73xxx

Steve Wallis

Why??• Although The Bachmann Std 5 is a

highly detailed model and has excellent slow speed performance, at full power it’s a relatively poor performer with a gearbox ratio of aprx 45:1, many other models of less powerful prototypes will easily run much faster including other Bachmann models.

The Branchlines Gearbox & Mashima Motor

• The Gearbox is by necessity a 40:1 ratio due to the driving wheel axle diameter being 3mm, any lesser ratio is supplied for a 1/8” dia axle.

• I would hope that in the future a 30:1 ratio box would be available to suit a 3mm axle.

• The Mashima motor is a 14/24, chosen for it’s higher top speed at full power. If a lower ratio gearbox becomes available a 14/26 motor might be a more appropriate choice.

Gearbox & Motor assembled

Getting the Chassis ready• To enable the

gearbox axle bearings to sit in the correct place for the axle, the motor has to sit much lower on the chassis.

Removal of the Mazak chassis material is necessary. If as I, you don’t have a milling machine, use an electric drill with a rotary burr.

Getting the Chassis ready (2)

• File out the oblong hole in the chassis centre to fit the gearbox train. 1.5 – 2mm is all that is needed to be removed from the sides of the opening.

• A file will suffice.

Fitting the gearbox• As mentioned

before it’s imperative that the axle bearings of the gearbox and chassis are aligned together.

Fixing the gearbox assembly to the chassis

• I used a marine sealant / fixing / bedding compound, past experience on my boat has taught me that the stuff is almost indestructible! Do not confuse this with cheap silicone sealant, which looks similar.

Fixing the gearbox assembly to the chassis (2)

• Just a small amount will do the job. Only apply to the chassis in the vicinity of the motor.

Fit the driving wheel axle• Fit the axle and the

final drive gear to the chassis.

• Don’t forget to tighten up the grub screw in the gear!

Leave overnight• After fitting the axle leave the whole

assembly overnight to let the sealant cure. Ensure that the underside of the axle is supported so that it sits in the correct place. I left it over a whole in a work-mate type bench.

Fit the Gearbox cover• Lubricate the

gears and shaft.• Bachmann’s

original gearbox cover can be refitted, file as necessary……………!

Fit the Gearbox cover(2)• ………….ensuring the cover doesn’t

foul the gearbox frame or motor mounting screws.

• Run the motor to bed in the gears etc.

The plastic under-chassis• The bad news is that more surgery is

required…………..

(I’d previously found the axles were binding on my model – hence the file marks!)

Plastic surgery• The new axle gear is larger than the

original, and the gearbox frame sides are also proud of the chassis underside. I used a Dremel type saw to cut away the plastic to clear the gear and frame….. However the pick up strips are also in the way and a section either side must be removed, and have new wires attached

The pick-ups• To ensure the stability of the pick-ups

place some sticky pad strips over the top.

More to do with the pick-ups!

• Drill a 3mm hole through the Mazak chassis from the underside to a point under the circuit board mounting, for the new pick-up wires.

Assemble the undersides• Fit front and rear driving wheels, thread both

sets of pick-up wires through the chassis, and run the motor to check all is well. Remove any plastic swarf or debris.

Assemble the valve gear• Fit the centre driving wheels to the

axle and ENSURE that you get the quatering to match the other diving wheels.

• Assemble the valve gear, and wire up the pick ups to the PCB, fit the DCC chip if you use one

Before continuing…..• You may want to add a flywheel to the

rear of the motor, however this will inevitably slow down the motor, I didn’t and cut off the rear motor shaft with a Dremel grinding wheel.

• You may have noticed in the previous photo that I have placed the speedo drive screw in the rear wheel, to help keep the connecting rod in position, whilst doing a quick (relative to previous!) speed trial.

Continuing• A fair bit of Mazak material has been

removed,• The model in it’s original form was a little

light anyway, and it lacked a bit of adhesion.• So see the next photo’s of lead addition to

the loco body and to the chassis.• BEWARE of letting lead having direct contact

with MAZAK, allegedly they don’t mix and the Mazak will deteroriate.

• Wrap the lead in insulation tape!

Putting on weightAn obvious location, if desired even more Mazak could be swapped for lead.

One piece of lead bent into shape and another strip added on the firebox crown.

Extra leadThe smoke-box is another obvious place, and insulation tape isn’t necessary here.

The finished item• Shown on a 1:40 gradient with 8

Bachmann Mk1’s in tow, minimal slipping.

• Unless viewing the underside, the mods are undetectable.

Speed?• There is an improvement over the

standard item, and also a standard item with a Mashima 14/26 motor. Although a 30:1 gearbox would have allowed a higher speed, it is none-the-less now acceptable with back-EMF switched off.

• Slow running is still excellent with a TCS DP2X UK chip with Back-EMF on (switchable on the fly with all TCS chips).

Post Script• Looking back through these photographs, it seems

that it took a leap of faith to commit to the surgery required to do this modification.

• However I also recall the disappointment with the performance of the standard model, and tried a new Bachmann motor and then a Mashima 1426 motor into the Bachmann gearbox, none of which vastly improved the performance.

• After a years worth of running, this model still performs magnificently, nothing has fallen off nor has the model ever needed any extra modifications.

• Good luck if you have the faith!