Starter "flat spot" - what's causing this?

[Richard J Lebens]

You would think the rebuilder would have done this but you could rotate
it around and measure the resistance across the brushes/windings to see
if there is a place on the commutator where the brushes are not making
contact.

If you are the physics or EE type you could view the current waveforms
on an oscope and see if you get a continuous series of even "humps" as
the current changes direction in a section of the rotor winding.

--- radek at istar.ca wrote:

> Thanks guys!
> 
> I took the starter out and counted the teeth on the flywheel:  lost
> track of the number 
> but all are OK.  Next, I took the starter to the rebuilder who put it
> in a vise and
> applied 
> power:  worked like a champ.
> 
> I'm going to clean up all electrical connectors and the housing where
> it attaches 
> to transmission, for good ground.  I'm also going to try to install
> some sort of 
> heat shield on top of the starter to protect it from the exhaust
> manifold.  It sits
> directly 
> beneath and the original heat shield had rusted out a long time ago.
>   
> Hopefully, this will cure the problem.  Looks like it's not been
> getting sufficient 
> amperage to operate, especially when hot (I understand the power draw
> will be 
> greater when the starter is hot).
> If all this doesn't help, it's rebuild time and it will be a
> different rebuilder.
> 
> Thank you for all for your help and support.
> 
> Radek
> 88 90Q
> 91 V8Q 5-sp.
> 
> > 
> > Message: 9
> > Date: Mon, 24 Oct 2005 01:23:25 -0400
> > From: Huw Powell <audi at humanspeakers.com>
> > Subject: Re: Starter "flat spot" - what's causing this?
> > To: Radek <radek at istar.ca>
> > Cc: quattro at audifans.com
> > Message-ID: <435C6FCD.4090004 at humanspeakers.com>
> > Content-Type: text/plain; charset=us-ascii; format=flowed
> > 
> > 
> > > For quite a few months now, my 1988 90Q has suffered from this
> intermittent
> > > problem.  Sometimes the car starts like a champ, other times you
> turn the
> > > key and ... silence.   There is power draw (voltage drops) but
> nothing
> > > moves, clicks or otherwise.  Total silence.  Push start.
> > 
> > If it's truly silent but you get a power draw, it's almost
> certainly the 
> > starter.  In the meantime, the old trick is to whack it lightly
> with a 
> > hammer to see if it will work on the next try.
> > 
> > > As a note, I found one way of dealing with the issue:
> > > When the starter wouldn't work, I put the car into second gear
> and rock it,
> > > trying to get the engine to rotate forward.  After such treatment
> it would
> > > often start. 
> > 
> > That might have had the "hammer" effect - or, if you don't get true
> 
> > silence but a click and whirring sound, you could be missing a few 
> > flywheel teeth, as suggested.
> > 
> > > However, a strange, grinding noise persists for a few seconds
> > > after the engine has started and then something disengages,
> everything
> > > returns to normal.
> > 
> > That could be the starter solenoid thing sticking and keeping on
> the 
> > flywheel after you release the key.
> > 
> > Prior to replacing the starter, I would use a test light on the
> starter 
> > trigger wire to make sure it's not the ignition switch at fault.
> > 
> > -- 
> > Huw Powell
> > 
> > http://www.humanspeakers.com/audi
> > 
> > http://www.humanthoughts.org/
> 
> 
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> 



	
		
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