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  #1  
Old 09-28-2009, 08:13 PM
vlittle's Avatar
vlittle vlittle is offline
 
Join Date: Jan 2005
Location: Victoria, Canada
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Default Matt Throckmorton's wrecked F1 Rocket

I noticed the bad news on Matt's site today http://www.docthrock.com/.

Looks like no injuries, but the aircraft was written off. Oil line let loose, followed by a quick landing and nose over/prop strike.

What I really took away from this is his engine tear-down. In particular, how his low time, 2-3 year old engine had unrepairable camshaft corrosion.

The corrosion did not cause his engine failure, but it's pretty clear that at some point it would have become a problem.

I hope the engine folks can chime in here. When I buy my IO540, I can't tolerate this kind of latent problem!

Vern
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  #2  
Old 09-28-2009, 08:47 PM
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frankh frankh is offline
 
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Location: Corvallis Oregon
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Default A real shame!

Another plugs for an engine dehydrator me thinks.

I didn't fully get how they worked...But when I realised that burning the fuel is what makes the water vapour..then water vapour at very high temp ends up in the crankcase (blowby). as it cools it will make a LOT of condensation..which then drips on the camshaft.

pushing minus 40F dewpoint air will mop it up in no time however.

Either that or fly it every other day will keep everything oiled up


Frank
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  #3  
Old 09-29-2009, 05:36 AM
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pierre smith pierre smith is offline
 
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Location: Louisville, Ga
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Default What puzzles me....

...is the fact that the crankshaft bolt was loose and backed out by 5 threads, according to his web site. That couldn't have happened on the noseover....seems like it was a problem that just hadn't manifested itself yet.

The loss of oil and the resultant feathering of the blades is what brought the airplane down, according to him.

Regards,
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RV-10, 510 TT
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  #4  
Old 09-29-2009, 05:48 AM
chaskuss chaskuss is offline
 
Join Date: Mar 2005
Location: SE Florida
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Default Internal engine corrosion prevention

Quote:
Originally Posted by frankh View Post
Another plugs for an engine dehydrator me thinks.

I didn't fully get how they worked...But when I realized that burning the fuel is what makes the water vapor..then water vapor at very high temp ends up in the crankcase (blow-by). as it cools it will make a LOT of condensation..which then drips on the camshaft.

pushing minus 40F dew point air will mop it up in no time however.

Either that or fly it every other day will keep everything oiled up


Frank
Lots of info on engine pickling on this recent thread. See

http://www.vansairforce.com/communit...ad.php?t=48554

Charlie Kuss
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  #5  
Old 09-29-2009, 07:17 PM
Hooznext Hooznext is offline
 
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Location: NW Ohio
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Default

Agreed Pierre, from the information he provided I don't see how that would be related to the oil line. Fortunately the airplane suffered the worst and everyone was able to walk away, but it looks like the issue with the bolt wasn't too much further in the future.

From this picture he posted, it appears the head was rubbing on something, also he commented about the pin shearing off in the gear the bolt was holding on.


Sorry to hear Matt....Glad you are alright!
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  #6  
Old 09-29-2009, 07:30 PM
kaye7877 kaye7877 is offline
 
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Location: Hoover, AL
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Default

I'm thinking that the dowel pin sheared and allowed the gear to turn, loosening the bolt. Not that the bolt was already loose.

For instance if the dowel could have been magically removed and the gear turned in the direction that would cause loosening of the bolt; then the bolt would back out as the gear continued to turn.

So, I'm thinking something stopped the crank and the gear kept rotating briefly.
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  #7  
Old 09-29-2009, 08:38 PM
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DanH DanH is offline
 
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Default

Consider the direction of rotation. Viewed from the pilot's perspective, the crank turns clockwise. If the crank stops suddenly, the inertia of the other rotating components tries to continue turning the crank gear clockwise....which shears the pin and tightens the bolt.

Two possibilities, given the evidence.

One, the bolt was already backing out before the accident. (Doc said the lock tab was "loose", whatever that means.) The sudden stoppage popped the gear out of its recess, and side load from the cam gear bent the bolt.

More likely, the internal crank threads were pulled when the pin sheared at stoppage and the gear tightened the bolt. When the threads gave way, the gear got cocked by the side load from the cam gear, which further pulled and bent the bolt. Might seem a little far-fetched, but consider how the bolt was thread-locked enough to break when he tried to remove it.

Crank gear mystery aside, I hope the lesson everyone takes away is that a dial indicator on the crank flange tells you zip about the accessory end after a sudden stoppage.
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Last edited by DanH : 09-29-2009 at 08:41 PM.
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  #8  
Old 09-29-2009, 10:01 PM
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MSFT-1 MSFT-1 is offline
 
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Default OK, I might be missing something here...

The picture of the gear with the retainer next to it suggests that the retainer was improperly used. The tabs are both bent in the same direction. Shouldn't one be down and one be up (thus keeping the bolt from turning)?

Even if you make the assumption that the tabs were bent to remove the bolt, I would expect that one tab would be bent "down" and the other straight out to the side.

Just a thought.
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  #9  
Old 09-29-2009, 10:20 PM
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Radomir Radomir is offline
 
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Default

It looks fine to me.. one tab is bent down (the one "facing" you) and two ears are the tabs that are bent up (they seem to have been bent up at some point, before the bolt head turned)...
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  #10  
Old 09-30-2009, 06:27 AM
mahlon_r mahlon_r is offline
 
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Posts: 1,025
Default

The issue of the crank gear, bolt and drive dowel is a situation that can occur with a prop strike. It is the subject of an FAA AD note and a supporting Lycoming Service Bulletin that requires inspection and or replacement of these items after a prop strike, because damage to these components can happen in varying degrees, up to what occurred in this engine, after a sudden stoppage.
The AD originally came out as 91-14-22 and was revised to this AD in 2004:
http://www.airweb.faa.gov/Regulatory_and_Guidance_Library/rgAD.nsf/0/9fa5e5f8683a0a4686256e9b004bc295/$FILE/041014.pdf
Good Luck,
Mahlon
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