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  #16  
Unread 11-21-21, 06:04 PM
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smoking gun

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......
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File Type: jpg smoking gun.jpg (19.6 KB, 1516 views)
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  #17  
Unread 11-21-21, 06:45 PM
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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.
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  #18  
Unread 11-22-21, 03:57 AM
wslade2 wslade2 is offline
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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.”

Last edited by wslade2 : 11-22-21 at 04:00 AM.
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  #19  
Unread 11-24-21, 09:57 AM
JAG JAG is offline
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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.
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  #20  
Unread 12-08-21, 10:44 AM
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Done - but engineers shouldnt set timing

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!
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  #21  
Unread 12-08-21, 02:26 PM
edasmus edasmus is offline
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This all sounds like good news. Good luck with the flight Tom! Report how it goes!
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  #22  
Unread 12-08-21, 04:34 PM
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Famous Skymaster lines...

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 __________"
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  #23  
Unread 12-08-21, 05:19 PM
stevew stevew is offline
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tough nuts

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
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  #24  
Unread 12-08-21, 06:19 PM
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access

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..........
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  #25  
Unread 12-08-21, 07:54 PM
stevew stevew is offline
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I sometimes wonder, while shoulders deep on the rear engine of a Skymaster……
If the Wright brothers had to work on the rear engine of a Skymaster, if they’d say…..”Let’s just stick with bicycles!!”
Lol🤪🤣
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  #26  
Unread 12-08-21, 09:43 PM
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I bet that rear engine access hatch mod is looking really attractive right about now...

Last edited by mshac : 12-08-21 at 09:45 PM.
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  #27  
Unread 12-09-21, 12:20 PM
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It is to me.
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  #28  
Unread 12-10-21, 12:09 AM
wslade2 wslade2 is offline
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Last I checked, the STC for that access hatch was pretty expensive.
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  #29  
Unread 12-10-21, 11:15 AM
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I am sure the STC is somewhat costly in comparison to what it is - cutting a hole in the firewall. I think Aviation Enterprises is the only one that has the STC. I have not talked to them yet, but do you remember how much it was?
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  #30  
Unread 12-10-21, 05:45 PM
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I wonder if you could buy one off a parts plane, like that yellow P-model that's being parted out on here? I attached a pic of the access hatch on a pressurized model, I have no idea if its different on a non-pressurized.
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File Type: jpg Rear engine access hatch 1.JPG (114.5 KB, 1437 views)
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