I just had my alternator rebuilt and I noticed that after I installed it that I can spin the cooling fan on the alternator, It can be spun with little bit of resistance, the belt is tight. Is there supposed to be a keyway on it? The 7/8 nut on the front of the alternator seems to be very tight.
Should I pull it back off and investigate this further or is it normal?

That is very wrong. yes. inspect before relying it for too long or voiding your warranty.


I thought it was a tapered fit, not a key. But either way, that bolt should fasten the fan to the main shaft securely.

...unless you have some sort of upgraded thing with a heat activated clutch - highly unlikely

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No it's not heat activated it's a normal Bosch alternator.
Darn it if I have to pull that thing off again.

Most of them have keyways on both the fan and rotor, but I don't always see a key installed. Instead, there is a thick washer between the fan and pulley and the nut gets jammed down super tight. I'd take it off and either install a key or ask the rebuilder to do it.

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The torque on the shaft nut is quite high. The spec for the alternators used in the mid nineties with a collar nut is 80 Nm.
Mercedes eliminated the key quite a while ago but as Mxfrank said, you could add one but the nut still has to be very tight.

There is a key way but re-builders leave it out and simply torque down the nut super tight. Looks like your rebuilder may have missed that step. The alternator has to come out and the nut tightened with an air impact wrench.

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85 300D turbo pristine w 157k when purchased 161K now
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

Ya, the Auto Parts store uses and Impact wrench wrench when they exchange Alternator pullies.
I do also. When I put the nut back on I use Loctite and the Impact Wrench.

I have 5 of the harbor freight type 12 volt Impact Wrenches. One for each of the 4 vehicles I have and an extra.
They are made for removing your wheel Lug Bolts are Wheel Lug Nuts but are almost as good as a pneumatic Impact Wrench but it depends on if you get a really good one or not.

The 12 volt impact wrench is very handy when it comes time to do tire rotation and speeds up a tire change on the side of the road where spending a lot of time changing a tire can be hazardous.

I used it once to remove a Crank Bolt (220 foot pound torqe) with no couter hold on the crank

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84 300D, 82 Volvo 244Gl Diesel