Lyka Kit #3 Differential (THE PIG!)

Below is an image I found from Wikipedia that best illustrates what the differential assembly looks like.

As an attempt to explain how this "Pig" works, a sprocket (which is not shown above) will be mounted to the left face of the assembly. This sprocket will be driven by a chain (much like a bicycle chain but much heavier duty) by the steam engine to rotate the complete differential assembly. The two shafts going out of the casing are attached to the two rear wheels of the Lykamobile. The smaller spur gears in the assembly lock the larger spur gears to the outer casing that is being rotated by the steam engine via the chain sprocket. The only time that the smaller spur gears rotate is when you are making a turn. The smaller spur gears allow for the "differential" of distance between the left and right wheel's travel when making a turn. In essence the small spur gears allow for the larger spur gears the freedom to travel or rotate independently. This allows the wheels to slow down or speed up on one side or the other so that you can make a smooth turn without the wheels skidding or jerking around on the pavement.


I have to say the differential assembly took some time. A fair amount of fitting, deburring and test fits and even so, I am a bit concerned that the free wheeling is a little too tight.


The first task was to press fit the bronze oil impregnated bushings into the smaller spur gears. Two bushing are pressed in from each side leaving a small gap in the middle. I used my vise fitted with plastic jaws to prevent any marring of the bushings.

Because the plastic jaws give a little I had to adjust the fitting a little by using a steel washer on both sides making a final squeeze in the vise to bring the bushings flush with the gear. I checked this using a straight edge looking for daylight.

Repeat 3 more times and then test fit the smaller spur gears into the two half cast casings.

All the smaller spur gears rotated smoothly and freely. Now comes the fun part ("The Pig"). Steam Traction World suggests that you pre-fit the larger spur gears on each stub axle. This took a bit of time getting the two opposing keys to fit the larger spur gear. Two issues I found. One was that the keyways in the stub axles were about 0.005 inches or so shallow causing an interference fit with the spur gear keyway. The keys would sit too high for the gear's keyway and would hit the gear. Once I corrected this interference, I discovered that the keyways on the spur gears were just so slightly off of center that prevented the spur gear to slide onto the axle. I had to adjust one side of each keyway on the spur gear by filing the keyway open a little bit. Each larger spur gear must be fitted and capable of sliding with slight pressure. You must spend the time to get this right to help facilitate the challenging assembly of the differential. The last thing you want is a stuck gear on an axle that you can't disassemble.
Next is to assemble the tapered bearing to one of the stub axles.

I used a piece of pipe to help tap the bearing along the stub axle. Not much force was required, I could almost just push the bearing on the shaft, but the pipe helped to keep the bearing parallel to the shaft.

I forgot to take a picture of inserting the tapered bearing on the other end of the stub axle, but you can just barely see the bearing in the following image where I have placed the steel spacer that sits on and next to the inner bearing ring on the shaft.

This is followed with a bronze bushing assembled over the steel spacer.

And placing the keys (180 degrees apart on the shaft) and sliding the larger spur gear onto the stub axle fixing it with the spring washer and M16 Jam Nut.

NOW FOR THE PIG ! Repeat the assembly of the tapered bearing on the stub axle and slide the stub axle into the right side of the rear axle assembly. Slide the inner tapered bearing onto the stub axle as shown below.

Place the steel spacer and bronze bushing on the shaft as before.

And then place the two keys onto the large spur gear. I had to use a little grease to keep the keys in position so they wouldn't fall out and then somehow begin to slide this all onto the stub axle without loosing any of the keys. The pictured below shows the keys resting on the flats on the stub axle threaded portion. I had to disassemble at this point to deburr the treaded portion of the keyway on this shaft so that the whole assembly would slide.

Next slide the spur gear and tap the stub axle to expose several threads on the axle.

You have to position all of this to allow you to insert the spring washer and M16 jam nut. And there is not enough room really to do this easily. I had to slide the jam nut as far as I could and use a punch to lightly tap the M16 jam nut into place by compressing the spring washer some. See below image.

At this point the stub axle is just protruding enough to hold the spring washer. Now using my right hand I apply pressure on the stub axle and twist the axle -- hoping to catch a thread and begin threading the jam nut onto the stub axle. It WORKS ! And I was able to do a final tightening of everything with an adjustable wrench.

Next I test assembled the two casing halves onto the large spur gears. I failed to mention that before you assemble the second stub axle you must place the chain sprocket on the left axle tube frame for later assembly. If you forget, its okay because this was just a test fitting of the parts and all of this must be disassembled for proper lubricating and greasing of the components.

Now its time to disassemble and grease everything for final assembly. I packed the bearings with grease.

Applied grease on all of the smaller spur gears and larger spur gears. Apply liberal amounts. More is better. Make sure you get that chain sprocket resting on the correct side of the axle tube assembly.

Repeat assembly of the first large spur gear to the stub axle.

Repeat assembly of the large spur gear on the other stub axle.

And squeeze the spring washer and jam nut together.

Tighten everything up. I discovered on the trial fitting that I needed to assure that the stub axles are pre-tensioned taking up the slack and providing clearance between the two M16 jam nuts. Because I have the rear wheel kit I slid the wheel hubs onto the stub axles and used regular automotive hose clamps to fix them temporarily and tension the stub axle assemblies.

 This allowed the separation of the two M16 jam nuts for final assembly of the casing halves.

I used Permatex #2 (non-hardening gasket sealant) on all of the casing mating surfaces - including the areas that clamp the bronze bushings. All assembled as shown below with painter's masking tape on the perimeter of the differential casing to allow me to degrease and touch up the primer. As I mentioned before the differential does work, but it is a little tight to my thinking. I think this is caused by a mismatch of centerlines between the left and right axles. As the differential casings are bolted together I believe it is forcing the two stub axles to align thereby creating undue pressure on the bronze bushings. We all know that the rear tube axle assembly is a weldment and that the alignment probably is off by 0.005 inch or so in my opinion. This I'm hoping will loosen up and wear in over time. If not, I'll just have to take it all apart and provide a little more clearance on the steel spacer where the bronze bushing rides. No big deal, just time.