A

asav8tor

Well Known Member
Mag drop was 75 L and 75 R Last year 100 tach hours ago.

Over the last year has increased to 100 L and 100 R

New spark plugs, no change.

Engine IO-360
4371, 4373 slicks
980 hours total
about 200 hours since mag inspection/new points

I know 100 RPM drop is well within limits. Question is should the fact that the drop has been increasing be of any concern?

And, what would be the possible causes of an increasing mag drop?


Thanks :confused:
 
Dual Mags

A good mag drop (within specs) is your indication that the mags are doing a good job developing horsepower, as when they are individually grounded that power is lost. Dual mags are not only for redundancy, but two flame fronts
produce a noticeable amount of extra power. So, embrace your healthy mag drop. (A timing check isn't a bad idea too!)
 
FWIW, I see a larger RPM drop with a leaner mixture. Running full rich at different density altitudes might have the same net effect.

Are you seeing a trend of increasing mag RPM drop under the same conditions with the same mixture setting?
 
Inspection

....about 200 hours since mag inspection/new points....


Was this a real inspection and yellow tag by a mag. shop, or a local take-it-apart, look at it and replace the points inspection?

gil A
 
The check has been done with the same RPM (1800), same mixture Full Rich, same altitude, airport, etc.

No I haven't checked the timing yet but will this week.

I didn't have the acft when the mag inspection was done. I see no yellow tags so I assume only new points and a look inside.

The interesting point is the drop was Exactly 75 per side, now it is Exactly 100 per side. I did not notice this happen all at one time. Best estimate is the 25 drifed off somwhere during the last 100 hours.

thanks
 
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Ideas

Mechanical or electronic tach???

Could this be a thing with the tach reading in 25 RPM steps???

As long as the drop stays the same on each ign, I would not be too concerned.

Can you hear/feel any difference since you indicated 75 drop???

Any difference in fuel??
 
Mechanical Tach.

Same fuel.

Feels and sounds same as before just an extra 25 RPM drop.

If it was just one mag that would have changed, I would pull that mag and go get it checked. But since they both are behaving Exactly the same I hesitate to pull them.
 
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