Alternators can be scary things. They play a crucial role in keeping your car going, and if they fail, can leave you stranded. More, as complex and intricate electrical units, they are not the sort of thing many would rush to disassemble should something need to be repaired. So why did I have mine open on the kitchen table the other night?
Well, after re-greasing the bearings on my tensioner and idler pulleys last week, I then noticed a bit of a rattle coming from the alternator. It wasn’t a lot, but high on the success of re-greasing the other bearings, and with an opportunity to learn something new, I decided to dive in and see what was going on inside the alternator. It proved to be fairly straightforward to get it open (you can find some decent tutorials online), and once I did, I discovered that the rear bearing was almost completely dried up.
With very little grease left inside, it was making a fair bit of noise, even when just spinning it round with my finger. Thankfully, it was a simple matter of cleaning it and adding some new grease to restore it back to what it should be. The short video below shows the condition of the bearing before and after. Once I added the new grease and put the bearing cover back in place, it spun in silence on the shaft again.
Though the front bearing appeared to be in much better shape, I opened it up anyway to see what was inside, and found a lot of old, nasty grease.
Making quick work of cleaning and re-greasing that one too, I began the process of putting everything back together. First I cleaned up some of the dust inside, and then began reassembly. The trickiest part is getting the contacts in the rear of the housing out of the way to clear the bearing. Again, you can find some tutorials online, but it basically involves sticking a pin in the hole in the rear of the housing to hold the contacts down; once you do, the whole unit goes back together quite easily. Get the front bearing started into its seat in the front housing, and use the pulley and your impact wrench to pull it back into place.
Now, to be sure, this is not a post on completely rebuilding your alternator. That would be well beyond the scope of my ability. And to be honest, I don’t even advocate doing what I did unless you have some good experience spannering. But if you’ve got the feel for these sorts of things, taking a few steps like this to keep your alternator running smoothly will help it work more efficiently, and give it a longer life. Yes, you can buy new bearings (I saw figures of about £20 each), but what I did here took me little more than an hour and seemed to be more than enough to bring it back up to snuff. You can see again from this short video below that the whole thing now spins smoothly and quietly.
After reinstalling the alternator, I drove around for a bit and was pleased to discover that all the noise was gone. A quick check with my multimeter confirmed that everything was working fine – the first photo shows the battery voltage with the engine running, the second with it off. I know it’s not the most comprehensive test to determine the alternator’s health, but it was sufficient to prove I hadn’t ruined anything.
Finally, here is a bit of a tech tip on how to easily reinstall your alternator.