This issue we look at the Alternator. This gadget uses some of the energy from the engine to make electricity to charge the battery as the engine is running and provide enough power to run the stereo, headlights, ignition and anything else electrical that you need.

In theory, the output from the alternator should be around 14.4 volts – putting a voltmeter on an earth point and the alternator output with the engine NOT running will show you the battery voltage. Once the engine is running, the output is the alternator output which is also about the voltage that you will get once the battery is fully charged.

If you measure the alternator output with the engine running and you are not getting 14.0 to 14.5 volts then you are not doing yourself any favours – higher will risk overcharging the battery, lower and you are not charging the battery sufficiently. If you additionally run a split charge system then your leisure battery is also not getting a full charge.

This article is for a Type 1 upright engine and a 50 amp alternator, however the principle remains the same.

Step 1 – Disconnect all batteries, I favour removing the earth connections first. Now you can safely work on the electrics. Then undo the big bolt on the alternator then carefully screwdriver / prize the pulley towards you, counting how many shim washers are on each side of it. Once the pulley half is off, hopefully you will find the woodruff key that makes the pulley turn the alternator. Save that for when you lose the new one!

Step 2 – If you have the original oil bath air filter, remove that by disconnecting the air hose at the top of the carburettor and unfastening the clips holding the filter to its tray. If you have non-standard air filter or other items limiting access, now is a good time to remove these.

Step 3 – Remove the carburettor/s if in the way as well. For this article, we have a standard Solex PICT3 which comes off with just 2 bolts at the base, the throttle cable (one bolt) and the air pipe.

Step 4 – Undo the bolts securing the alternator stand to the top of the engine. There are 4 of them, the front 2 are easily accessible, the rear 2 are a little more tricky. With the carb out of the way and a wobble bar on a racket, it just takes a little fiddling. A magnet can be handy to retrieve errant bolts! I also recommend putting a cloth or similar across the work area to catch nuts and bolts rather than them dropping on the ground or grass below. Also undo the bolt on the right hand side of the alternator that secures the metal strap. The strap keeps the alternator on its stand and is a very key component – if it is loose, you can create major cooling issues! You do not need to remove the strap just get it undone.

Step 5 – There is a plate at the back of the alternator flush with the main air housing / dog house fan cover. There are 4 bolts holding this in roughly north east, south east, south west and north west. The top 2 are accessible for a socket. The bottom 2 need a spanner and a good deal of patience – you may not get them all the way out depending on your manifold. Do not worry!

Once you get to this stage the alternator is now loose and you can move it somewhat. We got to this stage and really struggled and cursed. One call to the amazing Stuart at Sussex Air Cooled and he gave us the top tip that gave us our “Yee har” moment.

Step 6 – on either side of the main air box you will find a bolt downwards. Undo both of those so that the air box moves. Now being careful of the oil cooler behind the air box on the left side, tilt the whole air box backwards – you can push quite hard. Then lift the alternator upwards and rearwards and the 2 inches behind the black plate has a big fan attached. With some pushing, wiggling and a liberal amount of talking nicely, the fan will pass far enough to clear the hole and lift up and out.

As you can see from the picture, we had removed the carburettor and put a rag over to stop anything getting in. We also removed the distributor cap just in case of damage – no other reason.

Now at your bench, the bolt on the far end of the alternator spindle need removing. Hold the spindle in the vice and remove – you may need an impact tool or a lot of brute force. Again, once removing the bolt, watch out for losing the woodruff key. Ours is somewhere on the floor in a workshop in Pevensey Bay!

Reassembly is the reverse of the above process. For the woodruff key installation, you may find that Locktite is your friend to hold it in place on the spindle before offering up the next piece.

Torque the bolts up per the manual and ensure that as you turn the new alternator’s outer pulley half that you are turning the pulley to keep the fan belt from being trapped. The tighter you go, the more slack will come off the fan belt. Do not over tighten though.

If you removed the carburettor, now might be a good time to change the base gasket as well as you are there.

Test that the fan belt is moving as expected, because a fan belt that is not moving means no cooling.