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