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Unhappy Exhaust Valve

scard

scard

Well Known Member
Advertiser
Submitted for the Peanut Gallery.
This is an unhappy exhaust valve. ECI O320 550 hrs on this jug which I just pulled last night. I'm not seeking any advice, but I thought some might like a picture, and the commentary might be interesting.

 
Great pic, of unmolested (not touched or cleaned or grimey) problem.
Classic hot rim on that valve.
I wonder? did you notice it as a poor mag check, or hear a hiss in the exhaust pipe while pulling the prop thru on pre-flight?
Anyway, thanks for sharing.
 
Unhappy valve

Sure would be nice to hear more of the story. A pic may be worth a thousand words, but a pic and a history are needed to tell the whole story.
 
Valve

I will bite. Irrefutably caused caused by LOP operations with mogas, electronic ignition, fuel injection, high compression pistons, oversquare operations and the wrong brand of motor oil. Ha!
 
zav6a said:
I will bite. Irrefutably caused caused by LOP operations with mogas, electronic ignition, fuel injection, high compression pistons, oversquare operations and the wrong brand of motor oil. Ha!
Click to expand...

And the wrong primer on the firewall:rolleyes:
 
Obviously a nosewheel airplane......with a woman pilot.....
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Incoming! ;)
 
And

It only serves you right for having the ambition to pull jugs on New Years day. In a place as fun as Austin. Shame.
 
rocketbob said:
Interesting that the valve face is well below the seat.
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I see what you're talking about, but that is just an illusion in the picture.

DanH said:
Obviously a nosewheel airplane......with a woman pilot.....
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Incoming! ;)
Click to expand...
You can bet I told her she was doing it ALL wrong! :eek: Maybe now she'll listen when I tell her she should stick her tongue out the other side of her mouth when she banks right.
 
Somewhere in there is a joke about baking cookies------but I cant think of it at the moment;)
 
Looks like a hot spot at the 1 oclock position on the valve, where hot gas has been leaking through. Also see areas of corrosion on cylinder that look like trouble? Nice photo.

erich
 
It is funny all the stuff we're certain we see with modern processed camera images. These are actually iPhone 5 images, so you know they're all wrong :). Nevermind what might look like corrosion. It just ain't so (my eyeballs have been onsite), this engine flies three times per week. Just more picture funny business.
 
I pulled the full size pic off Picassa and zoomed in. Wow the 7 to 8-o'clock area around the outside of the exhaust valve seat looks bad. Not talking about the valve, or its seat, but the head around it.

Is cylinder head material missing / eroded / corroded away? Or it is just gaps in whatever crud has built up there? It looks a bit crumbly.

This is very interesting.
 
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So, the iPhone image processor does all kinds of dynamic image 'enhancement' that makes all of the combustion buildup look very bad. Remember, this is a carb that isn't very happy deep lean of peak. I think most of the erosion that you see is the buildup blown away. The interesting observation is that it is 180 deg from the failure point...
 
Scot

I see that you have practised this work before. Must be a bit frustrating.

Aside from all the giggles, I seriously doubt that there is anything you could do to cause this.

Quite simply, these kind of valve issues (often on genuine TCM jugs) are "birth defects" and when I assume, that these were replaced once before with the ECI ADa couple of years ago, they may well have been assembled poorly in the rush.

If ever there is a time for something like this to happen it is when the load is high and the pressure is on to turn around hundreds of customers "re-works".

I may be wrong...:rolleyes:

Bummer all the same.

Did you pick this up from boroscoping? Leak down or suspect it from an engine monitor reading?
 
Low Compression

While I think Dan may be right on the cause, Dave had the right answer on the 2nd reply - came in low on a compression test.

160HP running 100LL
 
Yay! What do I win :D

Sorry this happened to you guys. By the way since your website is gone I can't seem to finish my plane ;)
 
tcard said:
While I think Dan may be right on the cause, Dave had the right answer on the 2nd reply - came in low on a compression test.
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Seriously, regarding the underlying fault I'm with David from Oz.....a birth defect.

Besides, you're a great pilot. And the peanut butter things were great. And yeah, now I'm kissing up because I like my cookies orally rather than, well, you know. ;)
 
Bummer...

Wow, just saw this. Bummer Scott and Tanya. At least you guys caught it before something more severe happened. I'm headed to Amarillo on Sunday for a couple weeks. I was going to call you and see if you wanted to go to the Hard Eight the following weekend. Looks like that's out now. :(

Scott
 
The only way an exhaust valve can burn up with that little time on it is from a manufacturing defect. The seat or valve had some error in grinding. Over time a small leak develops and a portion of the valve starts slowly eroding. This is why when I get a cylinder from a shop I disassemble and laps the valves and use hi-spot scraping blue to make sure the valves seat properly. None of the manufacturers and most of the cylinder shops don't do this. I'm set up now to do my own seats now with a nifty set of tools to put a three-way valve job on. To my knowledge only Lycon does the same thing.
 
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Sorry for my absence in the technical discussion, real work happens, and I usually just come to VAF just for entertainment these days.
I've been watching this cylinder for about four months and about 125hrs. The very first indication, very early on, was from pulling the prop through. You feel three nice and tight cylinders and one that was becoming just a little more 'soft'. I did a whole lot of "just go fly and keep a close eye on it". We do 25hr oil changes, so on the next oil change, we did a compression test. Yep, it was down a little from its normal but still perfectly fine. It continued to get a little softer and the compression tests accelerated to the point where my arm is very highly calibrated. I can feel just a couple of pounds change now :). So, I'm paying close attention to engine instrumentation and the rest of the potential indicators. Next look, about 10-15hrs later, with compression still well in the 70s, I decided it was time to figure out exactly where the leakdown was coming from. This ain't rocket science. Pressurize the cylinder and stick an ear up to the exhaust stack exit. "Wooohhhhhh." We did a few of the normal 'valve gymnastics' while we continued to fly. No change. I kept a close eye on it with my now highly calibrated arm. As the compression fell into the 60s, it was clear to me what the end game was. I just had to decide for myself When. That point came this past weekend when Tanya wanted to go do a dog rescue for pilots-n-paws and I said "Sorry, you can't go", as I held my head in shame. The cylinder was off within 12hrs.

So, I've decided that I'm not going to fly around anymore without the ability to look inside my cylinders any ol' time I want. A Mills style 'borescope' is on its way and will be here tomorrow. Now to dump a little more fuel on this fire... I have another cylinder that I've been watching too! Same symptoms, same process, same progression, same product batch. It isn't quite there yet, but I'm not flying it until I'm able to take a good look inside. It might be off as well, depending on what I see this weekend.

Don't feel sorry for me. I enjoy this stuff. Removing and replacing a cylinder just isn't any big deal. "Field replaceable" design is my friend. My airplane likes to be maintained. Feel sorry for Tanya, she has to write the checks ;).
 
scott, do you have any info on the borescope you are planning on getting. cost, contact? thanks :)
 
turbo said:
scott, do you have any info on the borescope you are planning on getting. cost, contact? thanks :)
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Sure. I just ordered the first piece of junk off of Amazon that I found. We'll see if it works out with modifications. If not, my plan B is the ATS Borescope, which I may very well get anyway.

Amazon: "Sewell USB IntraOral Oral Dental Camera, 2 MegaPixel, 4 LED"
 
While we're on the subject of diagnosing things, can someone provide a link to an engine idiot on HOW to conduct a compression test that might uncover these sorts of things. and thanks!
 
S'cuse me , Bob, but ...

did you want a link TO and engine idiot, or a link FOR an engine idiot? :D:D

(sorry, couldn't resist.)
 
Well Scott, if you replace the e-bus diode, polish the fetzer valve, and reverse the master switch polarity this should not happen again! ;)
 
Burnt valve

Scott,
Lycoming exhaust valves have rotator caps that sit on top of valve stem and allow the valve to turn each time it opens. The one darker spot on that valve indicates a place where the valve was not transferring heat to the seat (should be a solid ring all the way around). I'm curious that the valve may have stopped rotating due to build up of carbon in the guide; Lycoming has all sorts of bulletins about sticking valves and reaming guides.
Mike Busch did a webinar for EAA that has info related to exhaust valves and it's worth 45 minutes of your time. I think it was last spring sometime.
Post a picture of the rocker box area around the spring seat so we can see if there is evidence of high heat around the guide.

Keep 'em flying.

Grub
 
scard said:
... That point came this past weekend when Tanya wanted to go do a dog rescue for pilots-n-paws and I said "Sorry, you can't go", as I held my head in shame...

... Feel sorry for Tanya, she has to write the checks ;).
Click to expand...

Scott, I think the least you could have done for her was to rent a Cessna or Piper for her to complete the PnP mission! ;)
 
Valve replacement

Ryan,
I think the exhaust valve would be replaced because at 500+ hours the chrome flashing has worn off the valve stem and I suspect has some abrasion from carbon built up inside the valve guide. Guide could be reamed and then dimensionally inspected; if worn it would be replaced. Valve seat should be fine as long it is ground/cut so the new valve has a proper seating surface.
Lycoming's transfer most of their heat through the valve stem as opposed to the seat like a Continental does. Lyc SI 1200A details the need for a very smooth surface finish on the guide so you have good stem-to-guide contact to enable heat transfer.
No need to replace the cylinder, just tidy it up as above.

Grub
 
Bob 'from fly over country';
As Scott C and others mentioned, you can start checking cylinder health every time before you fly.
The resistance you feel on the prop as you pull each cylinder thru the compression stroke is a good basic indicator. All compression strokes should feel the same.
If you think a cylinder is starting to leak out the compression, it can only go 3 places: Out the exhaust valve, past the rings or out the intake valve.
So during an oil change, when you have the cowl off, have a trusted assistant pull the prop thru, and listen at the exhaust pipe, oil fill tube and the air filter for hissing.
To find which cylinder, pull a spark plug out of each cylinder but one. Test again on that cylinder, don't hear a hiss, keep testing the engine one cylinder at a time until you 'hear the hiss'.
So to start, you don't need any fancy tools, just enough to get the spark plugs out.
More tools = more presice results, but that can get you started.
 
grub0927 said:
Scott,
Lycoming exhaust valves have rotator caps that sit on top of valve stem and allow the valve to turn each time it opens. The one darker spot on that valve indicates a place where the valve was not transferring heat to the seat (should be a solid ring all the way around). I'm curious that the valve may have stopped rotating due to build up of carbon in the guide; Lycoming has all sorts of bulletins about sticking valves and reaming guides.
Mike Busch did a webinar for EAA that has info related to exhaust valves and it's worth 45 minutes of your time. I think it was last spring sometime.
Post a picture of the rocker box area around the spring seat so we can see if there is evidence of high heat around the guide.

Keep 'em flying.

Grub
Click to expand...

I had the opposite, a valve that failed the wobble test in the "loose" direction.

The rotator did have a problem and the wear pattern on it at the rocker showed that it was not fully rotating.

Scott,

Was the wear pattern on that valve's rotator top surface even?
 
Scott,
Do you have oil analysis history? If so, were the nickel levels elevated?
 
az_gila said:
Was the wear pattern on that valve's rotator top surface even?
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I don't remember what it looked like, but also don't remember it looking funny. I'll take a peek next time I see it.

Doug said:
Scott,
Do you have oil analysis history? If so, were the nickel levels elevated?
Click to expand...
I stopped doing oil analysis a couple of years ago and started to force myself to never miss cutting open a filter (which we change on a very low interval).
 
scard said:
Sure. I just ordered the first piece of junk off of Amazon that I found. We'll see if it works out with modifications. If not, my plan B is the ATS Borescope, which I may very well get anyway.

Amazon: "Sewell USB IntraOral Oral Dental Camera, 2 MegaPixel, 4 LED"
Click to expand...

This one that ATS sells is identical to one at Harbor Freight for much less. It often goes on sale for around $150. I use it on a Continental O-300 and it has worked pretty good for inspecting cyl walls and valves.

ATS: http://www.aircraft-tool.com/shop/detail.aspx?PRODUCT_ID=MV-201

HF: http://www.harborfreight.com/high-resolution-digital-inspection-camera-with-recorder-67980.html

mv-201.jpg
 
Yes, you're right...Harbor Freight. I used a 20% off coupon on top of that so I was able to get it for $120...but I'm not sure if the clerk was supposed to apply the additional discount on the sale price.

If anyone in my area wants to try it before they buy, mine is located at KHAF and I would be willing to loan it out/drop it off anywhere within the $100 hamburger radius of my Cessna 170B (which is much smaller than the RV radius :D)
 
New Inspection Cameras Now

If you google " inspection camera usb 7mm" you should end up with dozens of small devices. $19 - $80 typically. I will be ordering one, as RFQ's are in the mail to a dozen suppliers. I'll give a report after tested.

+1 on RocketBob's comment, each valve/seat seal should be physically checked and lapped, not necessarily in that order. Aircooled engines are not tolerant of leakage, as you have shown.
 
Same Camera

I am still hoping to find out what made you pull the cylinder or did I miss it.

As to the dental camera, I have the exact same one and it is useless for the reason you stated.
I can look at my teeth though, not bad as long as I look at the brite side.:D
 
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