Alternator rattle

[stwat]

I have a gurring, rattleing kind of noise that im pretty sure is coming from the alternator. Its worse from cold start up but once warm only seems to occur at around 1000 rpm. I have noticed a few times that after a good long run the noise disapears altogether but after the car has cooled down, its there again.!!???? Could this be the bearings in the alternator?

I've also noticed when i rev the engine the lights get brighter, which in my experiance means that the alternator aint working as it should.

I spose my question is, could knackered bearings(if thats what the noise is) cause the alternator to not give full voltage on tickover?

Thanks,
Stu

 

[Ted]

I spose my question is, could knackered bearings(if thats what the noise is) cause the alternator to not give full voltage on tickover?

Thanks,
Stu

Stu, what you have described sounds like the bearings are failing - you could remove the fan belt, and check for movement and noise on the alternator.
Faulty bearings (unless they are completely shot, and the rotor is fouling the stator) will have no effect on the alternator output.
These days, an alternator should match the drain taken by the headlights while the engine is ticking over. and I would expect the lights to brighten a little when the engine is revved.
Best to measure the battery voltage with a DVM at about 2000 rpm - if it's more than about 14.5 volts you may have a problem with the voltage regulator.

hth......

 

[Ian B Walker]

Stu, if you need another altenator I just happen to have a spare one handy and I am in Rotherham on Tuesday, staying over at the Hilton Hotel in Garforth Monday night.