I recently noticed that my ammeter was moving very slightly about the null position, a behaviour that it does not normally exhibit. It had been some 40,000 Miles (64,000km) since I had last replaced the outer brush, so it seemed opportune to carry out an inspection. With the drive belt removed, the bearings can also be checked for both radial and axial play. Mine had some of the former which when new, you won’t notice any. They felt smooth to turn and had been in there for some 70,000 Miles (113,000km), having fitted them in 2008. It is a good idea to loosen the nut securing the pulley before removing it from the engine, so the belt is temporarily refitted. All the bolts on this 1973 18ACR are metric, so a 22mm socket is used for this task.
With the alternator now removed from the engine, I checked the brushes to start with. When new, brushes are 13.0mm in length with the typical minimum working length being 8.0mm. The inner brush measured 12.5mm whilst the outer was down to 8.5mm, so an ideal time to change it.
The brushes removed from the brush box can be seen at the bottom of the photo.
Next I decided to replace the bearings as the free play will only worsen which given the miniscule air gap between the rotor and the stator, could lead to contact between the two destroying both in the process.
In order to remove the bearings, the rotor needs to come out, so the pulley and fan are removed initially.
I use a 3” (75mm) puller for this task.
Next the two halves of the alternator need to be separated. There are three long bolts that retain the slip ring end (SLE) bracket to the drive end (DE) bracket . With these out, tap the DE bracket gently downwards so as to release. It is important to remember that the stator is only held within SLE bracket by the phase wires, of which there are three. Keeping hold of both will prevent any unnecessary movement.
The rotor is retained to the DE bracket by the bearing, while the SLE bearing and slip ring can be seen.
I used the same puller to withdraw the rotor from the DE bearing, which is held within the bracket.
Rotor now free of the DE bracket.
To remove the bearing from the DE bracket, the circlip is released followed by the retainer plate. The bearing can now be tapped out of the bracket, which will be followed by the pressure ring, the striker plate for the oiler and finally the oiler, which is just a felt ring. Fitting the new bearing is just a reversal.
The slip ring was noticeably worn when compared to a new one, in addition when viewed in strong sunlight, cracks could be seen in the plastic, both on the top surface and on the side. I had fitted it at the same time as the bearings back in 2008, so very opportune to replace.
The new slip ring alongside the old one.
Before fitting the new slip ring, the old bearing is removed. As I don’t possess a puller small enough at this stage for the task, I held the rotor gently in a vice and tapped the bearing from behind with a cold chisel, alternating from side to side until it was off. It only took a few minutes and this method also prevents any damage occurring to the rotor shaft, which is not case hardened. The new bearing is fitted by using a tube to rest on the inner shoulder and then with a hammer, tapped down into place. It does not need to make contact with the nylon pressure ring beneath, indeed there should be a small gap left between the two.
The new slip ring is fitted along with a new spring clip and then the wires soldered on.
The solder needs to be a high temperature type possessing high electrical conductivity, so I purchased a length from an auto electrical business that overhaul alternators and starter motors etc on trucks.
The rotor can now be refitted into the DE bracket bearing using a suitable tube such as a socket and the use of a hammer. With the rotor resting within the jaws of a vice and the narrower distance piece in position, the DE bracket is positioned over the rotor shaft and then driven into place.
The rotor refitted to the DE bracket. The wider distance is positioned prior to fitting the key.
The two halves of the alternator can now be reacquainted, tightening the three long bolts gently and evenly until all are fully home. The fan fits over and behind the key while the pulley locates on the key where it will capture the fan against the distance piece.
All back together.
The nut securing the pulley can be tightened fully once the belt is refitted.
Ron.