GTSO520's are very reliable if they are maintained well. I have 1200 hours on mine and never had a AOG.

Problem from what I've seen/heard/experienced isnt reliability so much as maintainability. They work great til they don't which then can involve a lot of painful, pricey, slow troubleshooting.

Pressurized the induction system looking for leaks...they weren't hard to find.
There were 4 leaks like this one...
[youtube]https://youtu.be/nibJ3lq435E[/youtube]

On those induction leaks, the clamps were tight, no gap visible.
After they fixed those I fired up to go for a test flight. Engine started and idled well, much better than previous flight.
Played with it a while, all seemed good. Headed down the taxiway and right engine started to slowly surge again. Stopped and did a mag check at 1500 RPM. Engine died on right mag...completely died. On previous mag checks the right mag dropped a bit more than the left, but not horribly.
Here are pics of the right mag guts...
Now everybody gets a trophy...every guess was right. Fuel problem, air problem, and a spark problem, just for fun. UNBELIEVABLE

Seriousness of your problems:

1. Mag
2. Crap in fuel lines
3. Induction leaks

I think the onset of your problem in flight was caused by the mag losing some gear teeth.

Probably good you approached the problem the way you did because if you looked at the mag first and fixed it the engine might have run ok but nor great. If you would have stopped then you wouldn't have opened up the injector lines and found the crap and the induction leaks.

Things have a way of working out right.

There is an AD (or SB) requiring engine shut down with a GTSIO if you have vibration. Vibration can cause the viscous damper to overheat the fluid. If the fluid breaks down, it will solidify and the motor will fail catastrophically. Sometimes you will see a heat signature on the drum.

This is the true culprit that caused the geared engine failures. This disc is what allows the GTSIO motor to run over 3,300 RPM. The gears were never the issue. Overhaulers were reusing the dampers, and most GTSIO pilots don't know the risk of vibration.

Seeing that mag makes me think you had real vibration. Consider replacing the damper.

Jack,

Nice find, how much time on the magnetos? May be a good motivation for the recommended 500 hour inspection of mags that few comply with.

Not sure if you considered the starter drive AD note inspection. It states any engine roughness that can not be corrected by manipulation of the controls would trigger the adapter inspection. Roughness may be a vague term and subject to perceptions by the operator. I do not particularly agree with this as we have replaced these starter adapters that have failed to meet the specification called out in the AD with brand new units from Continental that were right at minimum spec as received. The cost in not inconsequential either.

Yes, they do.
Good points...likely we would have fought #2 & #3 for quite some time before finding the problem.

Mags, vacuum pumps and tach generators should be inspected/overhauled every 500 hours on a GTISO.

A few weeks ago we lost the #6 cylinder on the left engine...that was a definite vibration. This was either all or nothing, couldn't really feel a vibration. But, like Steve said, roughness is such a judgement call.
Thanks, I wasn't aware of that whole issue, will look into it.

We're between 200 and 250 hrs on these mags.

Even on wet vacuum pumps?

Even on wet vacuum pumps?

What kind of Mags do you have? If they are slick( even pressurized ones) then consider some Bendix...

That is a Bendix mag.