The Chorehorse is a petrol engine powered battery charger. It can charge 12 volt lead acid batteries with a load of up to 10 Amps. It can provide a maximum of 15 volts DC at 300 watts. It is 14 inches high, 15 inches deep, 15 inches wide, and weighs 100 pounds. It was designed in Canada and served during World War 2. This one was made by the OUTBOARD MARINE & MANUFACTURING COMPANY OF CANADA LIMITED. It was also made in the UK by the BSA company, which normally produced motorcycles. Some models have a tubular protection frame, a silencer on a flexible hose, an electrically screened spark plug lead, and a canvas cover. Other models have a 30 volt output suitable for charging 24 volt batteries. Some models have a cast iron petrol tank (base), but this one has a cast aluminium tank (base).

Picture 1: Chorehorse Battery Charger

The charger consists of a petrol engine, with a slanted cylinder leaning away from the front. The left hand side has a cowling, which contains the flywheel, a magneto inside the flywheel, and a pulley, for a pull start. A rope can be wound on here, and this is used to turn the engine and start it. There is a small push button on this cowling, which shorts out the points, and stops the engine. The right hand side of the engine has the large generator. This also has a cowling over the moving parts. Mounted on this is the control box. This box has 2 bolts with wing nuts, for connection of the battery. There is an Ammeter that shows the current, either Charge or Discharge, with a scale going to 20 Amps. There is a large LUCAS button that can be used as an engine starter button. On the top of the box is a rotary control, which sets the field winding current, and so sets the output current. There are 4 brushes on the generator for the armature. This generator has 2 instruction plates. One says 15 volts. The other says 24 volts. However I think this is a 12 volt model.

Picture 2a: Instruction Plate (15 volts)

Picture 2b: Instruction Plate (28 volts)

The engine is a side valve type 4 stroke piston engine of 100 cc capacity, with a "short reach" spark plug. The normal running speed is 2200 RPM. Inside the crankcase are 2 cams that operate the inlet and exhaust valves. The connecting rod and timing gear splash the oil within the crankcase to provide lubrication. There is a governor connected to the crankshaft, which moves a rod to control the carburetor, and hence the engine speed.

The base of the generator is a cast aluminium fuel tank which can hold 4 litres of petrol. The engine crankcase is bolted to this. The crankcase can hold 0.28 litres of oil. Both of these have a refill plug that is a normal plumbers type blanking off plug. The fuel tank plug has an air release valve, so that the fuel can be used and the tank pressure equalized during operating. This is loosened during running, but tightened when the engine is stopped. There is also a drain plug on the fuel tank.

The exhaust pipe appears to be a piece of plumbers pipe. The silencer is clamped on the end. The carburetor is very simple, with a butterfly valve connected to the governor. There is a small pipe from the fuel tank to the carburetor main jet. This has a knurled screw on it for adjusting the fuel mixture. There is a choke cable that can restrict the air intake, which is useful for starting cold engines.

The BSA manual warns, that this generator is suitable for Signals type batteries of 75 Ampere Hour capacity, but not large vehicle batteries. The vehicle batteries may take a long time to charge, and the starting current may damage the generator.

The charger was in a very sorry state. It was dirty, rusty, had broken parts, and was painted GOLD. It sat in the shed for a few years. When its turn, arrived, it was cleaned. It was turned over and appeared to be not seized. I checked the oil in the sump, it was dirty but seemed to be filled to the correct level. I checked the fuel tank, and then added some petrol to the dry tank. I connected a good charged battery to the terminals. I pressed the start button. Nothing. The button did not move. I opened the control box, dis-assembled the start button and found it jammed. I removed the dirt and rust, and got it working again. The control box was reassembled. I pressed the button again. The engine turned over now, but did not start. I removed the spark plug, but left it connected so that I could see the spark plug gap. Upon pressing the button again, the engine turned over much more freely, but no spark was visible. I removed the flywheel and cleaned the points, and checked the points gap. The flywheel was put back on. This time when the engine was turning over, there was a spark. The spark plug was cleaned then screwed into the cylinder head. This time the engine turned over again, but did not run. I found the governor, and operated that by hand, but it had no effect. Under the carburetor, is an adjustment screw for the main carburetor jet. This time while it was turning over, I adjusted the jet. It coughed. Then a few more coughs. Then it began to run. I adjusted the jet for the best running setting, then released the starter button. It continued to run. There was nothing on the current meter, so I turned the control knob, and suddenly 10 amps was indicated going into the battery. Great, it all works, but it was mechanically very noisy.


The generator and engine was dis-assembled, and the parts put in boxes. The engine was taken apart. The big end of the connecting rod was so worn that there was a 1 millimeter play in the bearing. Except that there was no bearing! The aluminium connecting rod was running directly on the cast iron crankshaft. I searched on the internet, but could find no spare parts, new or old. I put the connecting rod on the mill, and removed 1.5 mm from the bottom end. When the bottom shell clamp was bolted back on to the connecting rod, and on to the crankshaft, it would not turn at all. I then put the connecting rod on the lathe and skimmed the big end hole just a little, making it round again. It had worn to an oval while running with all that slop in the bearing area. I bolted it back to the crankshaft and rotated it, but it was a little tight.


Picture 5: Connecting Rod

All the metal parts were sanded, to remove the gold paint. They were painted with grey undercoat. Then they were painted with green paint. The cams, piston and govenor were checked. The piston and head was decarbonised (scraped clean). The engine valves appeared to be good, and sealing.

Picture 6: HEAD GASKET

There was no head gasket, so a copper one was made, then annealed. The crankcase was bolted to the fuel tank. The barrel and head were bolted on. The carburetor was attached. The control box was rebuilt, then connected. A battery was wired on and it was cranked over. It seemed to turn over more quietly than before. Oil and fuel were added. It started after a little fiddling with the carburetor adjustment, then settled down to a steady speed. The air filter was fitted properly, as it had a makeshift clamp attached. This was removed and a correct length through bolt was added. The silencer was bolted on, although it had a big hole in it. The choke was reconnected.


The engine is normally started by winding a rope on the start pulley. The fuel release valve is loosened. The choke is pulled on. When the rope is pulled, the engine will turn over. The engine will then start. The choke can be released when the engine is running smoothly. The battery is attached, and the charging current is set with the control knob. The battery will charge. At the completion of charge, the stop button is pressed. The fuel release valve is closed. The battery is removed for use.

An alternate starting method is possible. A charged battery can be connected to the terminals. The large start button is pressed, and the engine will turn over. When the engine is running, the battery is removed, and the battery to be charged is connected. This is an easy way to start the engine.

Picture 8: CIRCUIT

The commutator positive lead is connected to the Ammeter, the cutout, a choke, then to the positive output terminal. There are 4 capacitors for filtering, and the choke as well. The cutout has the battery disconnected, until the generator is producing voltage, otherwise the field winding will drain the battery. The commutator negative lead, and the negative output terminal are earthed. The positive lead is also connected to the field winding, and the rheostat to control the field current (and hence the charging current).

The generator was used by the Signals section, for radio operating, and also by other field units. After the war, units were sold off for Home Lighting use.

Picture 9: Signals Use: Charging a Battery for Radio Operation

Picture 10: Armoured Car with Generator Carried on the Front Mudguard

There is a video of it running here...

The generator is easy to start and useful for charging batteries. It is quite to run, but very heavy.

Chore Horse Instruction Book & Spares List, Threestokes Limited

User Handbook for Charging Sets, E.D. 300w, 30v. (B.S.A.) January 1961

Ray Robinson