On 10/03/2020 10:44, Dave Plowman (News) wrote:
In article ,
Tim Lamb wrote:
Ha! Just been there.
Ancient tractor with no ignition warning light at start up. Initial
investigation found ample carbon left on alternator brushes so assumed
the fault was elsewhere.
Not so:-(
The alternator slip rings were worn down to the underlying insulation
leaving a narrow strip of copper either side.
As a temporary fix, refacing the brushes regained contact and the system
is temporarily working.

Seems odd the copper wearing faster than carbon but maybe this was a
recon alternator.

I've fixed quite a few alternators over the years, and never seen severe
slip ring wear. Perhaps the operating conditions of a tractor were the
reason - the fan in the alternator passes air through it. And dust etc
could cause more wear.

IMHO, 90% of alternator faults can be sorted by a new regulator.
Mechanical wear - except at a massive mileage - pretty rare here. The
other about 10% a failed diode, fixed by replacing the pack.

The one you've missed out is one of the bearings coming loose and
allowing the shaft to slide a little, so that the fan catches on the casing.

Once I could see where all the noise was coming from, I decided it was
okay to get me home. I later disassembled it and re-fixed the bearing.

SteveW