On Oct 18, 10:40*am, "Peter Dohm" wrote:
"Morgans" wrote in message

...

"twdeckard" wrote

I am sure you know all of this (grin), I just chimed in becuase its a
check best done on the run-up pad.

He did not say you shouldn't do it at run-up. *He was just pointing out
that your engine could run very rough if you lose one side while cruising.

--
Jim in NC

I am really not sure exactly what he tried to say; but, in his initial post,
it was clear that he had lost the use of all of one mag and a part of the
other--or the plugs or wires attached to it.

The problem with that is that mags have a couple of failure modes that are
common to all breaker point ignition systems in addition to the failure
modes that are peculiar to magnetos.

As far as I know, it is still a common practice to simply set the timing and
perform a runup type mag check as part of an annual and not open the mags to
gap and visually check the points. *That leaves the door a lot farther open
for the failure modes involving erosion of the points--which is related to
one of the two failure modes of the capacitor a/k/a condenser--and also to
wear of the cam follower. *Both of those failure modes usually make the
engine harder to start long before they will fail in flight, or at runup
test; but are masked sufficiently by electric starters that they can go
virtually unnoticed--unless the pilot is so dilligent as to carefully prime
and set the throttle and then count the blades on nearly every start.

Peter

To put several of your minds at ease, of course I did the conventional
both-right-both-left mag check at runup, but at 1900 RPM. I had not
had one bank of spark plugs go in/op ever until the in flight failure
a little while ago, and my post was simply to suggest pilots go to one
mag while at cruise rpm and engine loading to see what happens. In my
case the engine ran a bit rougher -- rpms stayed where they were set,
of course, because prop pitch changed to accommodate the reduction in
power.

I am sure I make lots of inadvertent errors when flying: missing a mag
check is not one of them.