"bds" wrote in message
...

"Andy" wrote in message
...
What do you mean by a power surge? To me a surge is a momentary
increase in something. Are you experiencing a momentary power
increase, or a momentary power reduction?

The PA28-180 I used to be a partner in experienced a few 200 rpm drops
at the most inconvenient times. It scared off 3 of the partners and
it took several years for me to find the problem. I became more
motivated after it happened to me during a high density altitude
takeoff.

It was caused by a P lead contact being shorter than spec. The P lead
contact pushes against the contact spring mounted on the mag
capacitor. The short contact didn't push the spring contact far
enough away from the rear mag cover and allowed it to sometimes arc to
the case. Dismantled the P lead contact and replaced the spacer tube
with a longer one from a spare P lead (same length as the other mag)
and the power loss problem has not been seen in the last 3 or more
years.

New mags, or even a complete engine rebuild, would not have fixed the
problem unless the P leads were also replaced. This wouldn't normally
be done since they are part of the aircraft wiring harness.

Really bad mag design since if the P lead comes unscrewed the mag is
shorted internally and behaves just as if the P lead is grounded.

Andy (GY)

Sorry - it is a sudden loss, not a sudden increase. Poor wording.

Thanks for the tip - we will take a look at this this weekend.

Bruce


To follow up on the P-Lead issue.. any short (break) in the old wire will
cause the problem as a bad P connector.
We traced one "mag" problem to the mag switch on the panel. Our PA-25-235
has two independent flip switches on the panel for the mags, one was bad.

We rebuilt one Mag 3 times in one day, it could not hold an internal timing.
We replaced the whole case.

BT