Fan fit on the alternator - reality check?

[spuggy]

Hey, need a reality check here...

Removed my old alternator. Tapped it a couple of times around the back edge of the center boss with the handle of a rubber mallet, it visibly loosened and pulled it off with one hand. As it came out of the car (fitted for a few, probably 4-5, years), dry, not lubricated.

The fan doesn't seem to fit properly on the new alternator shaft; the clue is that it won't go down far enough that enough threads are exposed for the factory nut to secure it....

The fan starts on the new alternator, but only a few mm - I have to almost immediately use the rubber mallet to get it to go down further. Quite quickly, the tone of the ringing when you tap it changes to "that's it, not moving any more". And sure enough, it doesn't. To remove it from there, I need to whack it fairly hard quite a few times (like 15-20) around the edge of the boss.

By way of contrast, to get the fan on my Bosch, I push it on by hand and tap it a couple of times with the mallet; entirely seated. And all the threads are showing. 2-3 taps loosens it for removal.

The original Bosch alternator shaft seems to have a diameter of 16.98 - 17.02mm. The new alternator shaft seems to measure 17.02mm and up; (some readings were bigger). Not much difference - but apparently enough. The inside of the fan hub is clean/shiny/uncorroded. A little assembly lube on the new alternator shaft makes absolutely no difference...

I obviously don't want to start whaling on a 40 year old magnesium fan. I'm also concerned that if I did manage to get the fan on, it may take so much force to get it off again that it won't come off in one piece.

I'm extremely reluctant to make the hole in the fan larger; seems to me that the fit of the fan on the Bosch alternator is correct/about perfect.

So I've contacted the vendor, but won't get a response for a while.

What say y'all? I'm presuming that "correct fit" is that the fan should be just snug/tight on the shaft before you bolt it up. Exactly like it is on the Bosch one.

Or should I try to open up the fan center a little?

Thanks!

[mepstein]

We get the old alternators rebuilt. Cost $75-125 and they look and work like new. I would not mess with your fan to make the new alternator work. It should be a smooth slip fit.

[spuggy]

Originally Posted by mepstein

We get the old alternators rebuilt. Cost $75-125 and they look and work like new.

The original alternator was pretty tired and was replaced 4-5 years ago with a Bosch AL400X - e.g. Premium Remanufactured by Bosch unit, about 4-5 years old. Nothing wrong with it - except it's rated at 75A.

Originally Posted by mepstein

I would not mess with your fan to make the new alternator work. It should be a smooth slip fit.

More I thought about it, the more I was leaning that way - but thanks for confirming!