Alternator rattle

[67westy]

I've spent the last couple of nights changing my alternator bearings as they were making a horrendous noise. Now all thats sorted there is a rattle from the alternator when the engine is at idle. As the revs increase this disappears. I'm fairly sure a bit of a rattle is normal, can anyone confirm? Alt strap and everything else in that area is secure.

 

[sparkywig]

There shouldn't be any rattling at all.
Have you checked everything (fan, fanhousing, etc) for tightness and alignment?

 

[67westy]

Arse, was not hoping for that answer! Everything is secure although I will recheck it tonight, the noise seems to be from the alternator. EVerything seemed pretty snug when it went back together although there was a fraction of up and down play in the shaft at the rear, but nothing looked particularly worn.

Maybe the fan isn't quite true or something. Spinning by hand didn't produce any noise

 

[sparkywig]

Even a fraction of play at the rear of the alternator shaft possibly magnifies to the fan rubbing the fanhousing.
Reach around the back of the fanhousing and see if there's any play by moving the fan.
There should be 2mm clearance between the fan and alternator backing plate as well.

 

[67westy]

Even a fraction of play at the rear of the alternator shaft possibly magnifies to the fan rubbing the fanhousing.
Reach around the back of the fanhousing and see if there's any play by moving the fan.
There should be 2mm clearance between the fan and alternator backing plate as well.

Cheers I'll check it out, I'm certain it's not rubbing but there was definitely a little play. The rear bearing was slightly loose in the recess on the back cover, I wasn't sure if it should be tight or not. There was a couple of mm clearance from the backing plate. Might have to take it all out again and double check everything, thanks for the help so far!

 

[mattd1984]

Also try taking the belt off and spinning the alternator round. May give you an idea if the noise only comes on when under load.

 

[67westy]

Also try taking the belt off and spinning the alternator round. May give you an idea if the noise only comes on when under load.

Spinning by hand didn't produce a noise, it's definitely under load but only at idle. As soon as the revs rise it all smooths out. Is it likely the belt could cause this if it's under or over tightened?

 

[sparkywig]

You can tell if the belt's correctly tensioned by twisting it through 90 degrees on the longest run between pulleys.

 

[67westy]

You can tell if the belt's correctly tensioned by twisting it through 90 degrees on the longest run between pulleys.

Cheers I'll give that a try too, I was doing the 5/8" method but it's a little difficult to judge accurately

 

[67westy]

Well I managed to get the noise spinning by hand, wasn't easy and it's only when pressure is in a certain place on the pulley but it seems like the fan is rubbing on the housing. I guess I need to take it out and maybe remove a washer or two to pull the fan in a bit. I'll also double check the fan whilst it's out, should it be completely true when it spins? Just worried it may not be totally straight as it seems to only rub on one side

Cheers!

 

[sparkywig]

The fan should be true otherwise you'll get an imbalance while it's rotating.
Make sure the shaft is straight by rolling it on a sheet of glass or something else that's a known flat surface.

 

[67westy]

Cheers, I'll give it all a thorough check. Wish I'd done this last time :roll: I knew the bearings needed changing so I assumed that would be the only problem. Lesson learnt!

 

[67westy]

Well it is all back together and working now Still not sure what caused the rattle but stripping and reassembling the alternator cured it, maybe something not quite seated right. Replaced the fan with a new twinport so hopefully up to maximum cooling now.

Thanks for the advice sparkywig!