[urq] alternator whine - SOURCE determined!!

[Geraint Lloyd]

you could try taping up some or all of the holes in
the back of the
alternator and going for a spin around the block or
run it on the jack
stands

just thinking that if you modify the air flow pattern
or size of the
aperture through which the air is drawn, then you will
also modify the
resonant frequency.
I am not suggesting you block off the cooling vents on
a permanent
basis, just try it as a diagnostic method

it that works then you might want to try blocking a
portion of a vent
hole to see if it shifts the resonant frequency far
enough out of range.
it might not take much.

incidentally, when you took the reg out, did the noise
get
quieter/louder or change in pitch?

i can see that you are probably going to end up with
an old vacuum
cleaner hose attached to the rear of the alternator
with duct tape and
zippy ties (not forgetting the LWB URQs GRP B
heritage)

Geraint



Brandon Rogers wrote:
> Ahh interesting thought - yeah the cover from both
my urq and 200 alts
> does not fit this one - bolt holes don't line up. 
The cover is missing
> in this case.
>
> Brandon
>
> -----Original Message-----
> From: Louis-Alain Richard
[mailto:laraa at sympatico.ca] 
> Sent: Monday, November 06, 2006 1:25 PM
> To: brogers at terrix.com; urq at audifans.com;
quattro at audifans.com
> Subject: RE : [urq] alternator whine - SOURCE
determined!!
>
>
> Technical question for all:
>
> In ETKA, the tin-metal back cover (à la urQ and
200q20v) is called an
> "intake cover". So, does the air enter from the back
to be pulled
> through the body towards the front and exhausted by
the fan? If so, then
> maybe the source of the noise is in the
absence/presence of said cover ?
>
> LAR 
>
>   
>> -----Message d'origine-----
>> Guys-
>> We have made progress. A few people mentioned this
possibility.  Drum 
>> roll please.....
>>
>> Alternator fan.  Creating a siren effect.
>>
>> We had the car on ramps and revved the motor - and
with your head
>>     
> right
>   
>> there - it was obvious.  So we swapped on a
different fan.  The 
>> alternator I have to use for this bracket is a
4kq/CGT that has a fan 
>> with a solid front face and fins on the back side. 
We swapped on a 
>> different fan, shimmed for identical pulley
spacing, from an urq 
>> alternator, which has the open blades and is the
same fan as the 200
>>     
> 20V
>   
>> alternator, and it made a pretty decent difference.
 The sound
>> (whine?siren???) is still there but not as loud or
as intrusive.
>>
>> I haven't had any time to do further investigation
or testing since
>>     
> but
>   
>> now I wonder if the location of the alternator -
_very_ close to the 
>> front valence, and poking out underneath by about
3/4", is creating
>>     
> some
>   
>> sort of air cavitation or something???? that causes
the siren effect. 
>> Any thoughts about what would quiet it down -
either blocking direct 
>> airflow or creating more airflow over the fan?  I
don't want to cut up
>>     
>
>   
>> the valence further for nothing....
>>
>> I do have pics of the setup I can send - will
hopefully have them 
>> downloaded in not too long.
>>
>> thanks
>>
>> Brandon
>> '84 urq 20V
>>     
>
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>
>
>   

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