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Knowledge Base - How To:- Alternator Seized ? Read On

Seizing up is a very common problem with MK1 & MK2 alternators, normally accompanied by some or all of these symptoms

  • A reluctance to start, very similar to a flat battery, normally happens when the car hasn't been started for a couple of weeks
  • A loud screeching from the engine bay when the engine is running
  • Clouds of rubbery smelling smoke from the engine bay
  • Broken or melted alternator belt

This is normally attributed to the alternator bearings having seized and is usually cured by replacing the alternator.
After encountering the this problem with my alternator  and stripping a few other alternators with "seized bearings" I've discovered that in most (but not all) cases the bearings are fine.
The problem is caused by rust between the alternator rotor and stator,  because of the location of the MK1/MK2 alternator water gets into the alternator and causes the rotor and stator to rust. When the car hasn't been started for some time (weeks rather than days) the rust builds up and stops the rotor turning, there's only a few thousands of an inch clearance between the rotor and stator and a fairly big surface area, so it doesn't take much of a build up to lock the rotor .... instant screeching, shredded alternator belt, clouds of smoke etc.

As a quick fix you can try is this. with the belt off, put a pipe wrench onto the alternator pulley and force it round, it will be pretty hard to move to start with and will then get freer, once it get to the stage where you can turn it be hand (probably 3 or 4 complete turns), refit the belt and run the car, should be fine.

Be warned though, it will seize again if the car is left sitting for a week or so, a more permanent solution is to strip it and repair as below

This is a MK1 alternator, but the MK2 is pretty much identical ( in fact a lot of them are interchangeable )

alt05

alt07

alt08

alt09

alt11

alt13

alt17


In the pic below you can  see the rotor on the right, the area of it that's painted red is what rusts up, clean it up with fine emery cloth and give it a light coat of paint to stop it rusting.
Stator is on the left, the corresponding area on that rust's as well, treat it the same way (be careful not to damage the insulation on the windings)

alt18

I've repaired a couple of MR2 alternators this way, it's very rarely the bearings, they are sealed and pretty substantial , this one is 20 years old, looks and feels like new ;)

alt14


Jimi Lawson
8/11/2010

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Created : 2011-06-13 17:19:17, Last Modified : 2011-08-27 10:39:33

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