Loss of an engine

[MelsML55]

My experience be it correct here or not.....if the rear engine alternator nuts ever come loose, the alternator will drop and let the oil out, just throwing it there.....happened to me IN MEXICO.

[TomM]

Excellent! Another easy thing to check, thanks for the insight!!!

[mshac]

Does your bird have the engine access hatch in the rear firewall? I've heard of A&Ps that didn't know it was there and caused themselves lots of extra work. Use it if you've got it!

[TomM]

Well, every now and again things just come together. I took off the cowling and looked at the back of the engine and found a gaping hole where a mag should be.......see attached. The drive gear was dislodged and stuck between the mag and the accessory case. I pulled the gear out and amazingly enough, found all the other parts to the drive side of the mag in the bottom of the cowling. All the bearings were still in the gear as well, and no marks on it. I am having a hard time figuring out how all that stuff ended outside the engine instead of all ground up.......My lucky day????

Obviously the nuts that lock down the mag just dont fall off in 1 minute - they work themselves loose, so this had been happening over time. My plane had been leaking more oil this year than last year, and I am going to point the finger at one of the mag hold downs coming loose. The other hold down was still in place, and must have been enough to keep it from rotating and messing up the timing. All my pre-flight mag checks are accompanied with a 75 rpm drop, match by both mags.....so no timing issues.

I spent the day taking off the cooling baffles and getting access to the mag. Next trip i will bore scope the accessory case to make sure all the gears look fine, remove the mag, check the parts and order any replacement items.

As a followup to mshac, my plane is older and does not have the access panel. It is on my list of things to do though......

[mshac]

Glad to know you got it figured out. How about a pic of all the parts you found in the cowling?

Like you said, those nuts didn't come off suddenly. Not sure how long ago your last annual was, but I'd be a little suspicious that the mags were checked properly.

I once had a mechanic forget to tighten the plugs after an annual. He had them in finger-tight. During the flight home, one of the plugs blew out of the cylinder. It was a Tomahawk, so only three cylinders left, and running rough as a cobb. I declared an emergency and limped to the nearest airport in a controlled decent as I could not maintain altitude.

Suffice to say, I never used that IA again.

[wslade2]

Did the rear mags not too long ago. Those hold down bolts are tough to get to and can see where someone may not have got one “tight tight”. Be careful on reassembly. Don’t be bashful about removing parts to get good exposure.

Without that rear access panel from the cabin (I don’t have one) accessing the rear magneto is problematic and probably what earns the skymaster reputation of “difficult to work on.”

[JAG]

This is not the first time on this forum we have heard of nuts coming off the accessory case on the rear engine. All these are hard to get at spots - so it is important to use NEW lock washers or NEW locknuts when installing mags, Alternators, etc.

Not so much on piston engines, but high frequency vibrations can also back nuts off the studs. I suspect though in your case Tom, it may have been worn out or improper hardware.

[n86121]

As I heard it said,

a Skymaster had an engine failure in Vermont, over the mountains, in winter, IFR at night.

The Controller asked, "Are you declaring an emergency?"

The Skymaster pilot replied, "No, I am declaring an inconvenience"

--

You are flying IFR, or night, or etc, and hear a loud 'clunk.'

Complete the following sentence, "Darn, I wish I was flying in a __________"

[stevew]

Tom,
Those mag hold down nuts are a bugger to get torque properly. I'm not surprised that they came loose. Hopefully you got the engine shut down in time and no damage.

When we got our 336, the mag mounting gaskets were shot and leaking all over the place. It was a pain to get the mags removed and replaced and properly torqued. Gotta take a lot of stuff off to get access to those nuts. Can't hurry it, just gotta bite the bullet and take stuff apart.

Steve

[TomM]

You are 100% correct....you have to remove things and take your time. Removing the baffling (which you have to remove other stuff to get out) lets you at least see the inside nut/stud. I taped the washer to a flexible shaft to be able to get it in there and slip it over the stud. The lock nut was easy enough to stick in a socket with an extension and get that in there - just have to find the right extension combination so that it is a little longer than the mag, but not too long to hit the firewall.....then it is one click on the ratchet at a time as you spend the next 5 min getting the nut to snug up......

With one mag out, the other is much easier to get at - I re-torqued those nuts too.

The alternator looks like it would be super fun to get out of there..........