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  #1  
Old 02-12-2015, 11:52 AM
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donaziza donaziza is offline
 
Join Date: Jun 2007
Location: Atlanta
Posts: 441
Default "Fretting" on a Sky Tec starter

There was a thread a couple of months ago with pictures showing a guy taking his Sky Tec starter apart and fixing it, AND, I realize there's a lot of you out there who probably know this, BUT, for those of you who don't, like myself, I pass this along in case it helps someone else.

About last summer, I began to notice what looked like "black grease" hanging on the bottom of my Sky Tec starter. I had two mechanics look at lt. No clue. I then called Sky Tec. Also no clue. A few days ago, there was a 3rd mechanic working on my plane, ( something unrelated), but anyway, he said he tightened up my starter. Not the mounting to the engine, but rather the starter halves themselves were loose. This allows the halves to grind on each other, making aluminum, and when mixed with a bit of engine oil from a small leak (right in the same place), looks exactly like "black grease".

Hope this helps someone.
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Old 02-12-2015, 02:16 PM
vic syracuse vic syracuse is offline
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Default Guilty

I am that "3rd" mechanic. It's the second SkyTEc starter I've noticed this on. Basically the starter is screwed together with 2 long bolts and they are held in place by the locking tabs that are bent up. Who knows why, but the starter halves get loose and any oil up on the front of the engine (what Lycoming engine doesn't have some oil leaks) mixes with the aluminum powder from the two halves rubbing against each other and it looks like the starter is leaking black grease.
Tightening the screws and rebending the tabs seems to stop it.

Vic
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Built RV-4, RV-6, 2-RV-10's, RV-7A, RV-8, Prescott Pusher, Kitfox Model II, Kitfox Speedster, Kitfox 7 Super Sport, DAR, A&P, EAA Tech Counselor/Flight Advisor, CFII-ASMEL/ASES, EAA Homebuilt Council
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Old 02-12-2015, 03:00 PM
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Default safety wire?

Would it make sense to drill those bolts and then safety wire them?
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Old 02-12-2015, 03:19 PM
vic syracuse vic syracuse is offline
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Default Kind of small

They're kind of small. I am thinking loctite if they continue to move.

Vic
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  #5  
Old 02-12-2015, 03:47 PM
PCHunt PCHunt is offline
 
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Default

Just guessing here, but if the bolts have tab-locks, it seems that they wouldn't be loosening. I suspect they may be stretching over time and due to hot-cool cycles and maybe vibration. Long bolts stretch more than short bolts.

I would think periodic tightening would be better than loctite.

JMHO, and YMMV.
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  #6  
Old 02-12-2015, 04:10 PM
sblack sblack is offline
 
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Default

could be a thermal issue. If the case is aluminum and the bolts are steel the force won't be consistent as temperature changes.
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Old 02-12-2015, 05:17 PM
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DanH DanH is offline
 
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Default

Which model Vic? I have seen the described looseness and fretting on an NL inline.
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Old 02-13-2015, 06:16 AM
vic syracuse vic syracuse is offline
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Default NL I think

Yes, it was the inline starter.

Vic
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Built RV-4, RV-6, 2-RV-10's, RV-7A, RV-8, Prescott Pusher, Kitfox Model II, Kitfox Speedster, Kitfox 7 Super Sport, DAR, A&P, EAA Tech Counselor/Flight Advisor, CFII-ASMEL/ASES, EAA Homebuilt Council
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Old 02-13-2015, 08:46 AM
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Toobuilder Toobuilder is offline
 
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Default

I just replaced my starter with a new NL and it started "making grease" almost immediately. Perhaps there's a big initial stretch of the bolts? Anybody have any repeat events after tightening the bolts?
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  #10  
Old 02-13-2015, 09:59 PM
tim2542 tim2542 is offline
 
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Location: Redding,Ca
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Default SAE threads in aluminum

I had the same issue, Skytec made me good on it but there is at least a small problem here.
SAE threads in the aluminum case is the problem IMO, if you see those screws loosen without the lock plates having opened then there is no doubt the threads are failing.
You usually will see thread-inserts when fine pitch screws are required in aluminum, in fact you won't often see fine pitch threads in cast iron either except the high dollar nickel alloys.
I mentioned my concern to Skytec, but they didn't feel there is a problem with the design. I'm watching mine closely for the aluminum oxide to reappear. If it does I'll install some Tineserts or equal.
One guys opinion....
Tim

Last edited by tim2542 : 02-14-2015 at 07:03 PM.
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