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Old 06-07-2021, 06:48 AM
BH1166 BH1166 is offline
Join Date: Nov 2017
Location: Eatonton Georgia
Posts: 708
Default Busch FEVA

I subscribe to Savvy, they run all uploads through their Failing Exhaust Valve Analysis/FEVA, looking for signs of pending EV failure. Per their analysis, a pending EV failure will have one anomaly of rapid EGT fluctuations/oscillation. I believe they have found 60 cases of this , further investigation indeed show pending/ imminent EV failure.
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Old 06-07-2021, 01:37 PM
scsmith scsmith is offline
Join Date: Jan 2008
Location: Ashland, OR
Posts: 3,087

Originally Posted by BillL View Post
Interesting information, but linking solely to the CHT is a bit of a handwaving stretch. Valve temps are mostly a function of the exhaust gas temperatures. There was a detailed research project on this in the NACA archives confirming that. The heat transfer and surface temperatures at the sliding interface of the end of the valve is certainly quite important, but to generalize about that from CHT is where the argument falls short of data.

I like the fuel fouling aspect as we know that it is not all oil and and oversimplification on my part. But, it is a fact that both will occur where the end of the exhaust valve is exposed when open the pulled back in to the guide area. That area is treated in design in different ways, some being a relief in diameter of the last portion of the guide to shield that length somewhat from deposits. Having rebuilt a couple of hundred auto engines and lived in the diesel/gas engine development world for decades, the bottom length of the guide is the most challenging and it can either wear excessively or seize up. Most engines have the wear issue then extend the length of the valve and port and do the shielding - - all factors challenged in the short overhead geometry of the opposed cylinder, aircraft design with limited lateral distance. Diesels can use a longer thin stems and port design to address deposits. They won't have direct acting rocker arms and only have linear forces (and action) for opening. I say diesels but they are typically also designed to function with gaseous fuels - landfill, propane, methane etc. Again, all compromise (balance) the design for the weight, life, cost of the specific application.

I like the tools, well done. Until doing one of these wobble/ream procedures, I did not realize that the lever spring removal is not ideal. A linear tool, like you made, is better for work flow.

That thermal plot of the exhaust valves (in the video) is interesting and greatly helps the communication of the situation! You did some excellent research.
I'm not convinced by the low CHT theory either, but I am actively running the experiment. My CHTs range from 240--290F on my angle-valve engine. After 600+ hrs, the exhaust valve stems look pretty darn clean. Of course I run very LOP. I also lean as I climb to maintain the same EGT that I have at take-off, and once MAP drops below 25", I lean to 50--75 ROP for the remainder of the climb. So I am keeping EGTs fairly high for the time I am running ROP. All these factors present less available lead to precipitate out.

I also don't buy the lead build-up story. I've scraped clean many an exhaust valve, and it seems to me the build-up is a combination of coked oil and lead. I have a hypothesis that if the valve is cool enough that the oil doesn't coke on it, then the liquid oil film from each cycle of the valve might receive a deposit of lead precipitate, which is then wiped clean by the next upstroke of the valve. So it doesn't build up. Given that Lycomings seem to have rather poor valve stem oiling, this may be non-sense...we'll see......
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Old 06-07-2021, 08:39 PM
mtnflyr mtnflyr is offline
Join Date: Mar 2019
Location: Boulder, Colorado
Posts: 22

Originally Posted by scsmith View Post
Thanks for posting pictures of your homemade tools. They look good. It would be even cooler to have a couple of pictures of them installed/mounted on the cylinder so we can visualize how they work if we haven't done this ourselves before.
I got caught up doing the work and didn't think about taking pictures. I still have to wobble test the other three exhaust valves, so I may remember to take pictures of the tools mounted on the cylinders. I'm a cheap Yankee by upbringing and make a lot of my tools and fixtures rather than buying them. Often they function better than what you can buy . . . and I learn a lot in the toolmaking process.
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Old 04-21-2022, 07:47 AM
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rv8ch rv8ch is offline
Join Date: Feb 2005
Location: LSGY
Posts: 4,700
Default exhaust valve lapping video

This was an interesting video:

Might come in handy some day...
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Old 04-21-2022, 08:11 AM
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jneves jneves is offline
Join Date: Aug 2021
Location: Livermore, CA
Posts: 189

Originally Posted by rv8ch View Post
This was an interesting video:

Might come in handy some day...
Saw this and almost every video Mike/Savvy has on YouTube. I'm a big advocate of learning all you can from people who know best. Mike B is a blessing to us in the EAB community. As much as he helps the certified guys get through maintenance issues with the best possible outcome at a reasonable price, he really brings a lot of value to us, since we can do our own work.

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