alternator bearing failure

[pradeep18061973]

Hi all,
recently i was stranded in the middle of the night after alternator bearing was broken.

I am not sure why this has happened..!

I will be grateful to anyone who gives me some idea on

why this has happened,
what are the things to look forward for avoiding this again
is it advisable to replace the entire alternator

it has been repaired by replacing the bearing for a cost of AU$170.

Thanks for all the advises.

[BMR]

Could be the belt was adjusted too tight. ...Or it was just its time to go.

[djb2]

An alternator front bearing should last just about forever with normal use.

The reason for failure is almost always a too-tight belt.

Most people don't understand the consequences, and just install the belts as tight as they can make them. Even mechanics will do this to avoid come-back problems with a squeaking belt. And when an alternator, compressor, or pump fails 10K miles later, that's more shop hours that isn't blamed on the belt install.

Properly working V belts require very little initial tension. They are designed so that an increasing load pulls them deeper into the 'V'. Friction is provided from the pressure against the pulley sides, not pulling against the bearing.

This doesn't work when the pulleys have "dished" sides, or are misaligned. Counter-intuitively, a nick or rough surface doesn't improve friction. It keeps the belt from sliding in deeper, and wears the gripping surface of the belt. Belts are made of very-low-stretch fibers, so a loose belt is probably worn down and narrower rather than stretched longer.

So check the pulley sides with a straightedge, feel for roughness and check the alignment when installed. Replace the front bearing, and install a new belt as loose as possible without it squealing too much at start. If this is higher than the recommended tension, check for problems. Front alternator bearings are almost always standard sized and easily replaced, about $10-$20 from a bearing supplier.