© Text and Photo: Frode H. Haaland
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© Text and Photo: Frode H. Haaland |
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Innstalling New Alternator1990 Discovery 200tdi |
| The charging light warned something was wrong within the alternator. As these are fairly cheap items, I just bought a new one, intending to put the old on the workbench later on. It seemed like a fairly simple solution, but problems arose as the new Prestolite alternator was not identical to the old Magneti Marelli, which in Land Rover terms are a Lucas not a Magneti Marelli! Confused? You're absolutely right! |
Diagnosis |
| The charging light came on as I pulled the key out of the ignition - and stayed on while vehicle being parked. Had to resort to jump leads to start after a few hours - and then the light stayed on while driving... Seems like a short within the alternator - worn brushes, bad rectifier (or just plain shorting due to dirt...). As Paddocks offered brand new ones for £58 incl VAT, I bought a new one, as the brushes only cost somewhere in the vicinity of £30. |
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The Lucas A127/65 (i.e. 65Amp) alternator looks like this inside.
#2 is the regulator and brush box assembly, #3 is the rectifier . both of which are suspect. #10 is the capacitor or suppressor which made things a bit uncomfortable. Actually my alternator had two of these, looking a bit different... |
Magnetti Marelli, Lucas and Prestolite... |
| The first (200tdi?) Discoverys used a Lucas A127
unit, while
later (300tdi?) used a Magnetti Marelli. Now this seems simple enough.
But it ain't. The unit on Otto (1990, 200tdi) is supposed to be a Lucas unit. And it looks like a Lucas unit. But it's made by Magnetti Marelli. MM is owned by Lucas, and produced Lucas alternators at Lucas' spec and Lucas designation, but with their own name/logo on it. So even if it says Magnetti Marelli on the label, it is still considered a Lucas alternator! On the other hand you have the Magnetti Marelli, which is basically the same as a Lucas, but used on later vehicles. Main difference as to enduser seems to be the lack of external resistorpacks (see below). |
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So when I ordered an alternator, I asked for a Magnetti Marelli
(while I should have asked for a Lucas) -
and got a Prestolite made to Magnetti Marelli spec...
Which is not identical to the Lucas, but very close. But still confusing when it all should be wired up... |
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| Old And New Unit |
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As can be seen, the old unit is very dusty, so it might just be a
case of dirt shorting the alternator out, but at 14 years old, it is
probably wise to have a new unit anyway - at least when they're this cheap.
The old/bad unit can be checked and repaired later on if it seems worthwhile. |
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Removal |
| Removing the unit is straightforward.
Remove turbo intercooler hoses for improved access. You will have to unplug the battery, as one of the wires on the rear end of the alternator is hotwired to the battery. Remove the cables, noting how they are attached, and then remove the bolt on the tensioner under the alternator. The long throughbolt on which the alternator swings is then removed - and the alernator will probably still stick to its attaching points. Gently working with a large screwdriver releases it. |
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Swapping pulley |
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The old pulley has to be moved over to the new alternator, and here the
different quality comes obvious of the old and new unit.
On the old unit, the spindle has a hex insert, so removal of the pulley is very easy. The new one has nothing to grip to, so tightening the pulley will be a problem. |
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| Where the old unit used a distance piece to align the pulley, the new Prestolite used a spring, which takes some time to wind onto the spindle. |  |
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Tightening the pulley to the specified torque is
important, but
difficult as there is nothing to prevent the spindle from rotating... I
resorted to using a wrench directly onto the pulley, as nothing else were
able to prevent spindle from turning when approaching the 65-75NM torque.
A file finished off the burrs made on the pulley. |
Resistors... |
| The old Magnetti Marelli alternator (i.e. a Lucas
unit... remember?), has two resistors fitted on the back. Both are fitted to
the chassis of the alternator, and a wire stretching from the resistor
itself.
One of the resistors has a connector that fits onto a spade connector inside the alternator, while the other is fitted to the wiring loom on the vehicle. |
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The new unit didn't have this spade connector...
Checking out what these resistors actually do, revealled they are not an integral part of an alternators function, but probably suppress radiointerference or something. There were also advice that they are not actually needed... So fitting them ill shouldn't be that much of a problem - and off I went. First resistor attached as on the old unit: onto the chassis (on one of the throughbolts holding the chassis itself), and to be fitted onto the wiring loom. |
| Next resistor made for another solution as there
were no spade connector.
I guessed it should be connected between postive and negative currents, so a short length of wire were fitted onto the positive pole of the alternator, and a spade connector to fit onto the resistor. Crossing fingers it would work and the advice given was correct... |
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Refitting |
| Putting the unit back on is straightforward, though
where the long, swivelling throughbolt attaches, has to be adjusted to
length, tapping the insert.
Fitting the wires were no easy, and then the drivebelt went on a were adjusted. The Prestolite unit from Paddocks were cheap - around 50% below the competition. But is was obviously of a cheaper make than the old unit, being apparant from the lack of possibility using an hexbit when tightening pulley, and also the use of a spring instead of a distance piece of the correct thickness. As no problem arose, and there is no noise on the radio, I guess I did wire the resistors correctly (or they are not actually needed).
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