Dual vs split magnetos

[jeckford]

Statement found on the web:

"we might as well address the design flaw of the Lycoming IO-360-A3B6D engine (the engine currently on our Mooney). The -A3B6D has dual magnetos to power the spark plugs (just like most piston aircraft engines), however the design flaw is the two magnetos are in a single housing and driven by a single drive shaft. The whole purpose of having dual magnetos is to have two completely independent ignition systems, which the -A3B6D does not really have. Fortunately the Mooney M20J is also certified to use the Lycoming IO-360-A3B6 (without the D) which has two truly independent magnetos."

 

I am looking to buy a M20J (first plane) which most come with the A3B6D engine.  I see a rare number advertised with the A3B6 (split magnetos) engine.

 

Are the Dual magnetos that big of a deal (i.e. risk of engine failure higher than split magneto?)

It seems like a lot of folks are flying around with dual magnetos...are you worried about falling out of the sky?

[Cruiser]

nope.

[Piloto]

nope also. On the 30+ years the magneto has been in the field there has never been a broken shaft or problem with the dual magneto. Unlike the oil pump that has a single drive shaft under torque there is no torque (no stress) on the shaft of the dual magneto. One advantage of the dual mag is that the timing of both internal mags is kept tighter since both are driven from the same shaft. It also makes it easier to change the oil filter since there is no magneto to block the access.

José  

[jetdriven]

i take a different view, there are a few single point failure modes of the dual magento which suddenly leave you without an engine.  However, if safety is what you are after, spend the 5-6K it costs to convert your Mooney to dual mags and get yourself shoulder harnesses, an EFIS, second attitude indicator, onboard weather, moving maps, training, IFR rating, aerobatic training, etc.

[HopePilot]

I have the dual magneto and it gives me that warm, gooey feeling that only 5k can buy.

[KSMooniac]

I'm comfortable behind the siamese magneto, but only if the 500 hr service intervals are strictly observed, and if the mounting nuts/clamps are checked at every oil change.

[tyrefoote]

I was told that my J had an off airport landing due to failure of single mag.  It has the Independent mags

[tyrefoote]

I meant, it now has the independent mags

[testwest]

KSMooniac is *exactly* correct, as he nearly always is.

We have the siamese mag as well, and almost has a problem, the case of ours broke at the interface to the engine (due to a loose clamp, natch), luckily the mag is so tight to the firewall it did not fall out. It was only a 15 minute flight, I was ferrying the airplane to our AMT for annual time.

Overhaul every 500 hours, and check those clamps. We have the Lopresti cowl which has large inspection doors on the upper surface. I reach in to the engine compartment through those doors on preflight, grab the mag and give it a shake to make sure it is tight, before every flight.