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11-06-2015, 07:15 PM
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Join Date: Jan 2008
Location: Ashland, OR
Posts: 2,561
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Question for cylinder head gurus
My friend has been learning to use a boroscope.
He sent me a link to a you-tube video of a valve opening and closing. Please take a look: https://www.youtube.com/watch?v=Kxeb...ature=youtu.be
If you look closely, you can see slight movement in the valve seat as the valve contacts it. I think it is oil that is squeezing out of the seam between the seat and the cylinder head.
I would have thought the seat should be pressed into the head tightly and shouldn't move.
Is this bad? OK? typical?
Should this be addressed immediately? Soon? Let it go until something bad happens?
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Steve Smith
Aeronautical Engineer
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11-06-2015, 10:01 PM
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Join Date: Dec 2008
Location: Big Sandy, WY
Posts: 2,567
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Its not pretty when a seat pops loose. They have an interference fit and shouldn't leak.
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11-07-2015, 05:20 AM
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Join Date: Mar 2009
Location: Rochester NY
Posts: 669
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Seems not okay - not typical.
Personally, I wouldn't fly the aircraft until this is resolved.
FWIW.
Dan
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KC2ZEL
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11-07-2015, 07:08 AM
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Join Date: Sep 2014
Location: Central Tx
Posts: 172
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That is a failure waiting to happen.
Keith
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Keith
329DR RV10-bought flying
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11-07-2015, 08:01 AM
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Join Date: Sep 2007
Location: Central IL
Posts: 5,514
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First it is loose when cold, then it is loose when hot. That's bad.
I know of one engine was highly turbocharged and had a tapered shape on the seat, it was chilled in then a die pressed on the head to yield material on the seat. It was the only way it could be made to stay in place. I don't think this applies to the NA-Lyc.
How many hours on this head assy? Maybe now is a good time to have a new (oversized) seat installed.
Edit - nice clear picture with that scope - what specs does it have?
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Bill
RV-7
Lord Kelvin:
“I often say that when you can measure what you are speaking about,
and express it in numbers, you know something about it; but when you
cannot measure it, when you cannot express it in numbers, your knowledge
is of a meager and unsatisfactory kind.”
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11-07-2015, 09:37 AM
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Join Date: Dec 2009
Location: Montreal
Posts: 1,456
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Ya that was my question - what borescope is that?
Sucks to find that, but very good to find that on the ground before a lot of collateral damage to the engine or worse. I think I need a borescope. Sorry can't offer any wisdom.
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Scott Black
Old school simple VFR RV 4, O-320, wood prop, MGL iEfis Lite
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11-07-2015, 10:03 AM
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Join Date: Dec 2014
Location: hilltop lakes' Texas
Posts: 135
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Quote:
Originally Posted by scsmith
My friend has been learning to use a boroscope.
He sent me a link to a you-tube video of a valve opening and closing. Please take a look: https://www.youtube.com/watch?v=Kxeb...ature=youtu.be
If you look closely, you can see slight movement in the valve seat as the valve contacts it. I think it is oil that is squeezing out of the seam between the seat and the cylinder head.
I would have thought the seat should be pressed into the head tightly and shouldn't move.
Is this bad? OK? typical?
Should this be addressed immediately? Soon? Let it go until something bad happens? |
It appears the valve guide is worn, I wouldn't call it critical. There lots of this out there on high time engines. Is it good?, no. |
11-07-2015, 10:19 AM
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Join Date: Feb 2006
Location: Valley Forge, Pa
Posts: 636
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Quote:
Originally Posted by 8 ball
It appears the valve guide is worn, I wouldn't call it critical. There lots of this out there on high time engines. Is it good?, no.
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That's my impression also. the rocking motion of the valve in the worn guide is causing uneven pressure on the seat.I've seen this failure in type IV VW cylinder heads that are run hot.Great work with the bore scope in finding this early.May I ask how many hours and who's cylinders are these?What oil are you using? The guide wear is common issue,the seat movement is not.I wouldn't fly it till the jugs are pulled and sent out for repair.A loss of one cylinder in a Lycoming will spreed debris to the other 3.Much cheaper&safer to Top this engine now.IMHO
RHill
Last edited by rhill : 11-07-2015 at 10:33 AM.
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11-07-2015, 10:48 AM
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Join Date: Aug 2009
Location: Southern California
Posts: 877
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Seat Movement
Quote:
Originally Posted by 8 ball
It appears the valve guide is worn, I wouldn't call it critical. There lots of this out there on high time engines. Is it good?, no.
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The valve seat should not be moving. Period!
Skylor |
11-07-2015, 04:58 PM
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Join Date: Dec 2012
Location: N.C.
Posts: 144
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Valve seat/ guide
Looks like a combination of both a worn valve guide and a loose seat. I certainly wouldn't fly it until I resolved the issue. The cost of an overhauled or new cylinder is minimal compared to potential damage if left unresolved!
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