Group Poll: How many hours between mag overhauls?

On 24 Apr 2005 19:29:31 -0700, "nrp" wrote:

Presently I have Slick 4200 (4201 and 4251 as I recall) Series mags on
a Cessna 172M.

The timing to the engine has not changed since the initial new
installation, and remains within specs. They are now at about 900 hrs
since new. This is flat country so I 'm leaving them alone for now.

I've never experienced a rough mag since I quit renting aircraft 1600
hrs ago. I'm now at 1700 hrs TT over 40 years all (well most) with 80
octane or autofuel.

My alleged experience is derived from private owner-flown aircraft,
rental/trainer aircraft, corporate-owned/professionally flown
aircraft, and charter aircraft.

Average annual utilization of all these types was around 400 hours a
year-the higher utilization of the last three types pulled down by the
first type.

If you are telling me that noone has has to twist your Slick mags in
900 hours, I believe you-but I will say that this is not the norm in
my experience. In theory, the plastic point "cam" stuck into the split
shaft is supposed to wear at the same rate that the points erode,
keeping the point/gap internal timing relatively unchanged. You're
probably living right, it never seems to quite work out that way for
me.

As I indicated, on company aircraft, we yanked them at 500 for
inspection and pitched them at 1000. We figured it was a small price
to pay to eliminate the "rough mag since I quit renting" problem
you've mentioned. On customer aircraft, internal inspection was
predicated by a couple of small mag-to-engine timing changes or one
large one.

Regards;

TC

I guess I have followed the practice mentioned by others... if they are
Bendix, check the points & clean out at 500 hours while doing the
impulse coupling check. Follow SB599X

The old slicks with the plastic cam needed attention every couple
hundred hours. Newer ones seem to last like the bendixs.

So I find points with a little wear at 500 hrs, but OK; at 1000 hours,
usually replace them and they are good to go till tbo.

On the slicks, the dust from arcing in the towers will often short
out the distributor caps. So it's a good idea to clean the distributor
caps while they are out.

Sure there are two. What do you do when you fail a mag check
in Bum---- Nebraska on a Sunday?

Bill Hale A&P

One trick I have used to minimize the electrical stress on a magneto
and the related ignition harness is to make sure the plugs are gapped
to the minimum permissible gap. This minimizes the chance of
encountering a random failure from high voltage.