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Spinner Surprise

KJBSouth

Well Known Member
While completing an oil change this weekend, I pushed on the spinner and was surprised it wiggled. The prop was on solid. But, the whole spinner including the backplate to which the cone is fastened, moved. I unfastened the cone from the backplate; sixteen screws around the perimeter. Could not see any problem, but the backplate behind the prop wiggled.

So, yesterday I took off the prop and found this:
Spinner1.jpg


The center of the backplate was bolted behind the prop solid to the aluminum crankshaft extension, and the rest of the backplate was floating free.
Spinner3.jpg


Apparently 350 hrs of vibrational flexing of the backplate against the edge of the crankcase extension had fatigued the backplate so it cracked. It's not something that could be seen without pulling the prop.
Spinner2.jpg
Spinner4.jpg


I already have a new backplate ordered and its on its way.
 
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Interesting prop spacer you have on that crank. What make / type prop are you running.

Is there a front spinner bulkhead on your installation? Were the screw holes worn there causing the flexing?
 
I'm interested to know why you think it cracked. Could the spinner be that off that it would put enough force on the backplate? Do you know the manufacturer of that backplate?

Thanks for any more info.
 
Does the prop spacer that is installed by chance have a very sharp edge around its perimeter?
Was there a forward spinner bulkhead installed? You only mentioned removing screws from the rear bulkhead…
 
Was there a forward spinner bulkhead installed? You only mentioned removing screws from the rear bulkhead…

That is what I was thinking. Without a second plate to create a sandwich type structure, the spinner would be free to follow an imbalance and wobble, creating heavy stress on the one bulkhead. Easy to see how that leads to fatique fractures in the alum.
 
Back prop plate.....

Holy C**P! :eek::eek: I would guess there was no front plate to stabilize the spinner, leaving it free to wobble. One of the reasons pushing up and down on the spinner is one of the items on my preflight checklist.....:eek::eek: Did the prop show any damage....?

Order a new front plate if you don't have one already.....and make sure the spinner is screwed to it!
 
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My guess would be that there are no screws in the forward spinner bulkhead.
Was a dynamic prop balance ever done ? It can make a noticeable difference.
 
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