What does a dead alternator rotor look like?

[maclariz]

Just wondering if there is a problem with my alternator rotor. How do I find out if it has been fried to above the Curie temperature of the magnets? It is on a GS400 and has three magnets, but each seems to have four poles, alternating North-South-North-South along its length (as tested using a small fridge magnet). Should it be this way? Or should it be a simple bar magnet with a north at one end and a south at the other?

[TheCafeKid]

Alot of times a dead one looks just like a live one. And its common for your rotor to have a group of mags rather than a solid peice. I have two that are the same way in my basement. Both funtion normally.

[maclariz]

Alot of times a dead one looks just like a live one.

So how do you test one?

[Redman]

Do not know of a test for the rotor magnets.

There are electrical test of the stator coils.
.

[bwringer]

You could get a rough idea by comparing the strickiness of the rotor magnets with the rotor on another GS. The magnets should be quite strong -- it's normally a bit of a struggle to pull the stator cover off a GS, and they'll attract any iron in the vicinity. When the cover is off, you have to be careful not to allow and bolts of iron debris to stick to the magnets. It'll easily hold up a large socket wrench, for example.

I used to have a GS400 aeons ago, and the rotor magnets were very weak. Maybe it's endemic to that engine -- I was told sometimes the rotor magnets just get weak over time, but I don't know if that's true or common.

[SPARKSS]

So how do you test one?

Look it over for mechanical damage (mounting bore and magnets) and then....

I'd mount it with a known-good stator and see whether you have acceptable output. If you do, and it doesn't fly apart or cause vibaration when revved up, I'd call it GOOD.

That is the best way.