Thursday, March 24, 2016


The engine is ready, the body is being painted and I'm left with my unsuccessful "special tool" attempts to open up the transmission. I thought I'd better give it a break so I took on the generator. You can find priceless literature on the net about the electrics, just like any other component.

The generator consists of the simplest electrical components and produces a maximum power of mere 60 Watts. For comparison, my 2008 BMW F650GS produces 400 Watts. A modern nay regular headlight bulb needs 55 Watts. I do want to clean it up a bit, but my main purpose is to understand how it actually works - call it "professional interest"...

It's very easy to produce electric. You just need to rotate a wire loop in a magnetic field fast enough to create electric field and that induces the current in the conductor, which is the rotor windings on the right in the photo above. The rest of the system simply limits this uncontrolled electric current within the operating range of the system and ignites a spark in the plug in the right time. 

So where's the magnetic field then? It's easy, too - if you don't have a real magnet, wind a wire around an iron core and apply electric. Here - you made an electromagnet. This is the rear side of the generator, the four windings on the sides are connected to the battery, they are our electromagnets.

The rotor sits right in the middle of them and uses the magnetic field they create. The disadvantage of this setup is that if you run out of battery, zou can't jump start the engine.

The R25/3 was the low end model, possibly therefore they chose a cheaper and more compact system instead of having a real magnet. By the way, look at the poor state of the paint.

Let's remove the parts one by one. First the plate on top, held by two screws. This is responsible of the ignition timing. Think about it how you would push your legs when swinging; the spark must be ignited at the right time, in synchronization with the compression cycle of the air-fuel mixture so that the energy created by this "mini explosion" adds up to the next cycle.

The timer rotating above the center hole touches the conductive pin every half cycle and causes a spark. You actually need a spark every two revolutions, so three out of four sparks are wasted but this makes the system so much simpler. The pin sits on a little arm with a spring on it, which is an "emergency valve" to safely discharge in case of an overload. 
The two so-called brushes collect the electric generated in the rotor. They are pressed onto the rotor contacts with two little springs behind them. The generated electric then goes to another electromagnet, which limits the current to protect the battery and bulbs. And it does that only with a mechanical switch. When the voltage rises, it pulls the switch off and cuts off the system. When it falls again, it switches back on. And it does that very fast and continuously. Just imagine yourself controlling the lamp in your living room that way! 

It's fairly dirty inside, as I remove I also try to clean them but it is not easy with all these tiny details. As all the components were removed, I took the entire body in spite of the electromagnet windings and soaked in detergent water and dried using the hot air gun. Still not clean enough, though.

This is a high voltage transformer, connected to the spark plug via the soldered wire in the middle.

When the timer touches the pin, it transforms the 6-7 Volts on one side up to something like 15-20 thousand Volts for a fraction of a second and feeds to the spark plug. The spark plug is just two electrodes separated by 0,6 millimeters of distance. The high voltage is able to jump this distance, thus creates a spark between them to ignite the already compressed air-fuel mixture. 

As I remove, I renew some of the old and tired cables.
After the cleaning, I begin to sand the cover and body. It's a hard job, but the principle is so simple and extremely effective. You take a few different "grit" sandpapers, soak them in water and apply starting with the coarse (smaller grit) and proceed with finer. The result is good.

The generator body is steel and has to be painted but I decided to leave the aluminium cover as it is. It isn't possible to undo the scars on the cover anymore, time is cruel to all of us.
After a good enough weekend for the paint job, it's now time to bring it all back together. 

This is the front end of the crankshaft. A "woodruff key" fits into the notch on it. The spline on the inner face of the rotor slides onto the key and avoids any slippage while rotating. 
The rotor sits into its place with one or two mallet blows. 

I found a pleasant detail that I didn't notice while removing. The ignition timing adjustment is usually a tricky job with a special device. Luckily, this one has a notch on the timer so it can only sit in one position relative to the rotor. So I only have to make some fine tuning, if at all.
Screwing the body onto the engine and attached the timer with the center bolt. New screws, new plastics, partially new cables...
There is one last adjustment to make. The gap at the tip of the "emergency valve" I mentioned above (that is not a scientific name, I made it up) needs to be 0,4 millimeters wide. It is just a screw adjusted by loosening and tightening a nut each side. I adjust the gap and check with the feeler gauge. Done.
And last but not least, the front cover. I will need to open it again to connect the wiring harness, but until then better keep it tidy. I feel more and more energized and motivated as the old and tired parts get together again, much cleaner, much brighter and much fitter. Looks beautiful! What's left is just the wheels and the transmission that I still couldn't open yet. The end is near...