Hobbs vs. Tach for mag overhaul

[RV7A Flyer]

My Hobbs time is a little over 500 hours now, but tach time using 2500 RPM (my usual cruise RPM) is around 432.

What do you all use for the interval for the recommended magneto overhaul? Tach or Hobbs? I know tach time relates more closely to the theoretical grand total number of revolutions, which is what *should* determine wear and tear, but is that a good measure? Or just the total accumulated time that the engine (and hence mags) are turning?

[rv6builder]

I'd use tach time because its going to be less than your hobbs... More bang for the buck! In all seriousness maintenance is usually based on air time, therefore tach time should be the most accurate.

[BillL]

Yeah, if you are looking for a realistic hours to wear number use the tach. It is just a reference, though, as the care, maintenance, and luck have definite effects regardless of how the hours are measured. Clean air, clean oil, get it hot each use and use it frequently and often. Look at Vlads results. Water is a killer.

[tim2542]

If it?s an impulse coupled mag, I?d not delay the inspection.
Tim Andres

[mike newall]

Gents.....

It is a Service Bulletin, not a mandated event.

Your choice.

If all is well, carry on. If you feel something needs attention, then attend to it.

I may recommend that you choose to do it on a calander time rather than an hours based thing.