M47 alternators by Duncan

User avatar
Now most people know that the alternator on the diesel is renowned for failure. Many people experience failure shortly after a service where oil has been spilled on the alternator. I inspected one of these and noted the brushes were stuck, because the oil had caused the brush dust to stick together instead of blowing away.

So imagine my surprise when mine failed. I've been massively careful about oil, and it's never seen a drop in my possession. OK it could have happened before I bought it, but it looked spotless and had been with me for three years and a fair few miles without a problem. This weekend I pulled the cover off to inspect the brushes, and they were clean as a whistle, and plenty of life. So I did a couple of other checks, and found the rotor is very high resistance. It should be a few ohms, but was actually tens of thousands of ohms.

I haven't pulled it apart any further to see why, but I suspect it's location at the front of the engine halfway up has allowed salt water in that has corroded the windings. It did happen just a few minutes after the car had been washed, so maybe that finished it off?

I'll have a deeper look and report back!

Posted 01 Aug 2012, 19:37 #1