Loss of an engine

[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.

[TomM]

The plane is done and put back together. Initial run up was good. Gonna fly it this weekend to verify oil leakage. Installed all new hardware on the mag, including the rubber drive gear bushings. The cost of aircraft parts is crazy....the rubber mag bushings are only $6 a piece (which surprised me how cheap they were), but the junky little snubbers that are mounted on the #2 cylinder valve cover and push against the oil cooler are $125.........that is crazy.....But from what I have read on them, you need to replace them about every 500 hours so they dont wear on the oil cooler. So I took care of that as well.

I spent over an hour trying to time the mag so that the lights and buzzer would indicated that they are EXACTLY in time. I got it where they were within about a 1/8" (at the end of the blade) rotation. Finally the mechanic grabbed me and the buzz box and took me to 3 planes with the cowling off and showed me that none of them set the box off at the EXACT same time.....he said that if I could get them to do that I should buy a lottery ticket. When I read both mags should be timed at 20 degrees, the engineer in me says that what they really mean is 20.000000 +/- 0.000000 degrees........

I am excited to be in the air again and am thankful that my mechanic is open to supervising my work. Thanks for the input on this project!

[edasmus]

This all sounds like good news. Good luck with the flight Tom! Report how it goes!