This is a good looking exhaust valve with a nice concentric appearance. However, the compression was very low at 8/80.
I lapped the valve, hoping it would improve the compression test result… it only came up to 10/80, and that was after running the engine again and getting it nice and hot.
Although the valve face showed a healthy appearance, the seating area was telling a different story. Check out the following borescope photo of the seating area showing a possible leaking area:
It appeared there was abnormal wear on the valve seat, and the valve was not able to seal well, causing an unacceptably low compression result.
Listen to the audio for more details on this one.
I asked the question, “Borescope or compression tester… which one is better?”
Let me know what you think after listening. I’m curious to hear your thoughts.
Just click the button over to the right and record a brief audio message for me.
Thanks!
We ended up sending cylinder #5 out for repair, and then reinstalling it.
We did a test flight today, and everything went very well… ready to go for another year!
Here are some links to information on cylinder / engine break-in procedures:
This fuel injector line must have only been attached finger tight when the fuel injectors were reinstalled after cleaning. The engine ran fine at first, but all of a sudden during one engine run, the #5 EGT took a nose dive, and the #5 CHT immediately started dropping off as well.
The above photo was taken AFTER we discovered what the problem was. I’m guessing the nut was not tight, and it worked itself loose, causing the cylinder to immediately cease firing, since the fuel was no longer being sprayed into the injector nozzle.
Joe hired me to help troubleshoot the situation. We got on a Face Time call, and I asked him to show me the #5 induction pipe and coupling area, and all of a sudden, he noticed the #5 fuel injector line was not attached…
I was sure this was the culprit, and we were both thrilled to have solved the mystery. In our minds, it would be a simple fix, and Joe would be back in the air again.
Not so fast… since the cowling was off, Joe decided to inspect all the cylinders with his borescope. And that’s when he noticed a bigger problem. Joe noticed the exhaust valve in cylinder #2 did not look good, and he sent me some photos.
That is a really bad looking exhaust valve, with three green edges… one at 1 o’clock, one at 4 o’clock and one at 9 o’clock. The edge at 1 o’clock even looks like it has a scalloped edge, a sure sign it is severely worn.
This valve is too far gone, and is not a candidate for lapping in place. The cylinder needs to come off.
Wow, maybe the issue Joe had with the #5 cylinder was a blessing in disguise, since it prompted him to borescope all his cylinders, and that’s when he found the burning exhaust valve in cylinder #2.
Well done Joe! I’m glad you found these issues before they became an inflight emergency.
A borescope is a necessary tool in maintaining piston engine cylinders, and they are surprisingly affordable these days. I recommend the Vividia VA-400 from Oasis Scientific. It’s the one I use. If you’re considering a borescope you may be asking, “Which borescope should I buy?” This is a great question, and I did a podcast episode about it a good while back. It’s episode 115, and you can find it here: “115 – Which Borescope Should I Buy?”
If you decide to buy a Vividia VA-400 (or another model by Oasis Scientific,) you can check it out here:
And remember to use the code “Dean” for a 10 % discount. (This code only works when purchasing from Oasis Scientific, and I appreciate you doing this, because it helps me out as well.)
Ways you can work with me:
Hire me to review your borescope photos.
Hire me to do maintenance records research.
Hire me for one-on-one consulting.
The details and pricing for these services are on the store page of my website:
I received an email recently from Spence, the owner of an S35 Bonanza with a Turbo-Normalized IO-520 engine. He included a picture of his #2 cylinder exhaust valve. Here’s what it looked like:
At first glance, my reaction was something like, “Oooh, that’s ugly!”
The most concerning area is the spot at the 10 o’clock position. There’s also a little concerning area at the 2:30 position as well, but not as much as the 10 o’clock position. The normal deposits seen on the top and bottom edges of the valve have been burned away over at the 10 o’clock position. The small red spot is concerning, but not as concerning as if it was green. As it says in the excellent exhaust valve poster “Anatomy of a Valve Failure,” produced by AOPA, “Green means stop!” This is because the color green has been seen on valve edges that are imminently in danger of a piece breaking off.
For sure, Spence’s borescope photo is a classic visual presentation of a burning exhaust valve. Perhaps you’re wondering, “What does “burning” mean?” And that’s a great question. It means there’s an area that is not sealing well between the edge of the valve and the valve seat when the valve is closed. This condition allows very hot exhaust gases to rush through a small gap between the valve and seat at just the wrong time when those gases are the hottest, and over time if left uncorrected, the edge of the valve can suffer extreme heat damage and finally be in danger of a piece of the valve breaking off.
Not something you want to risk while you’re flying along in your Turbo-Normalized Bonanza! (Or any airplane for that matter.) But an airplane with a turbocharger is especially vulnerable because even a small piece of an exhaust valve would be enough to completely trash the turbocharger.
The next question might be, “How would you know if an exhaust valve was burning?” This is also a great question. You might see a drop in compression, but the best way by far to find a burning exhaust valve is with a borescope. With some training in what to look for, a burning exhaust valve is very noticeable, as in the photo above.
Spence did a great thing when he found this burning valve. Finding it was one thing, but deciding what to do about it was the next big question. In his email, Spence asked, “Do you believe this is a candidate for lapping in place and is it something you would be able to do for me?”
Spence was very interested in a less-invasive way to remedy his burning exhaust valve, especially since he has had other cylinders fail this way over the years, and this particular cylinder had only 368 hours on it (he actually paid a reputable engine shop to take the new Superior cylinder, check the exhaust valve tolerances, and perform a 3-angle cut before installing the cylinder.) He was understandably weary of changing cylinders.
I agreed to give the lapping procedure a try, with a couple conditions. One, we would not want the exhaust valve guide to be significantly worn. And two, the edge of the valve and valve seat must be in reasonably good condition.
On the agreed upon morning, Spence showed up at Classic Aviation at KSHD, and we got to work. We got things opened up and before removing the valve springs, we did a cold compression check and could not get more than 30/80 psi, with significant leakage past the exhaust valve. A healthy cylinder should be a lot more than 30/80, even with a cold compression check.
We got some borescope photos of the valve edge and seat, and aside from the normal spotty appearance, things looked quite good.
After removing the valve springs, our second condition was also met, in that the valve guide did not have a substantial amount of wear. I checked this by wiggling the valve stem up and down and side to side, in various positions.
Now it was time to perform the lapping procedure. “Lapping an exhaust valve” involves removing the rocker cover, exhaust rocker arm, and valve springs. This allows you to carefully push the valve into the cylinder far enough to see the edge down through the top spark plug hole. In this position, you can carefully apply valve grinding compound on the seating area of the valve, rotating the valve as needed to lightly coat the full 360 degrees of seating area. At this point, pull the valve back against the seat and rotate it back and forth using whatever method you decide, in order to restore a good smooth seal between the valve and the seat. I use a wood dowel rod chucked in a cordless drill, with a piece of thick vinyl tubing clamped between the dowel rod and the valve stem, which acts as a shock absorber and works very well. It may take several rounds of applying the compound and lapping the valve, and rinsing it off with solvent in between times, letting it run out the bottom spark plug hole onto a shop towel.
It’s important to rinse the valve edge off each time in order to examine the progress. My biggest regret from this particular lapping job, is that I did not take incremental photos along the way. It was by far the best result I’ve ever seen. After the first round of lapping, there was a nice smooth even band most of the way around the valve, with a distinct darker uneven area for about 30 or 40 degrees of rotation… corresponding to the burning side of the valve. After the second round, the bad area was noticeably smaller, and after the third round, even smaller still. We did a fourth round of applying the coarse grit compound for good measure (the bad area was pretty much completely gone at this point,) and finished it off with one round of lapping with fine grit compound.
The result was nothing short of spectacular:
This is about as perfect of an exhaust valve edge as you could hope for! Needless to say we were thrilled.
We washed the cylinder out with some Av Gas in a squeeze bottle, blew it out with compressed air, and repeated that process a second time. Then we sprayed some LPS-2 in the cylinder for some lubrication so the cylinder walls would not be dry for starting.
We put everything back together and installed a new rotocoil assembly P/N SA629117-1 on the exhaust valve, and a new rocker cover gasket.
Spence did a short ground run so we could check for leaks, and then he did a test flight to check engine operation and get it hot so we could do another compression test.
While Spence was out flying, I cut the old rotocoil apart, and was SHOCKED at what I found: (I had heard of this happening, but had never seen it myself.)
The spring inside the rotocoil should be one long continuous spring. This one was in many pieces, clearly making this part non-functional. The rotocoil serves a very important purpose. It causes a small and incremental rotation of the valve every time the rocker arm presses against the valve stem, and helps to maintain a good seal between the valve and valve seat. When an exhaust valve stops rotating, there is a much greater possibility for a hot spot to develop. It’s important to stop a hot spot as soon as possible. If not, cylinder removal may be inevitable.
We are very hopeful this cylinder has been rescued from premature removal. Not only did the lapping process restore an excellent seating area on the valve, but the compression came up dramatically as well… after the test flight, we got an amazing 70/80!
Thank you Spence, for the opportunity to work with you on your cylinder! Of all the valve lapping projects I’ve done, this one is a favorite for sure.
The result was absolutely amazing, and I have a few takeaways as I think about the whole valve lapping process:
Even low-time cylinders can develop exhaust valve problems.
ALWAYS do a borescope inspection along with every compression test (preferably with every oil change.)
Take action immediately when you notice a burning exhaust valve (lapping is often a good solution if caught early.)
ALWAYS install a new rotocoil assembly when lapping a Continental exhaust valve, to help ensure the valve will rotate properly and consistently.
If you do remove a cylinder for repair, be sure a new rotocoil is installed as part of the repair process (sometimes they are reused unless you specify otherwise.)
If you’d like to see or hear more info on this topic, be sure to check out episode 109 of the Airplane Owner Maintenance Podcast. It’s called “Exhaust Valve Problems – Could Lapping Be A Good Option?” Apparently airplane owners want to learn about this topic… episode 109 is the 4th highest downloaded episode of all time, do date.
I got an email from Michael this past week. He owns a Mooney M20J, and something strange happened with cylinder #1’s EGT and CHT recently. Michael agreed to let me share the story, so that’s the main feature in this episode. The picture above is one Michael took with his borescope while looking for any obvious problems with the cylinder.
Before we get to that story, here are a few items I included in this episode:
How I microwaved a fork, and nothing bad happened 🙂
How I’ve been fighting the mice at Classic Aviation.
The great people this week who either stopped by the shop to say hi, or who sent me an email or voice message:
Mike, and his Cirrus SR22.
Steve and Janet, and their Twin Comanche.
Rudy and his Mooney M20J.
Michael and his Mooney M20J. (This is the featured story in this episode.)
A little follow up from the Piper Saratoga story I talked about in the last episode
… and here’s the little basil plant that has become more interesting than I ever thought it would:
Here are a couple more samples from the excellent photos Michael took of cylinder #1 with his borescope:
Finally, for those of you who love great books, especially books that use good aviation stories to teach life lessons, I have a good one to recommend.
John Ramstead has a new book coming out real soon called “On Purpose With Purpose.” From his days as an F-14 Tomcat pilot, to a near-fatal horse-riding accident, to his transition to a podcaster, speaker, and coach, John’s book is absolutely inspiring. I’ve already pre-ordered my copy, and I’ve been reading the digital version… it’s excellent!
12/80! That’s a terrible compression test result. And unlike some cylinders, this one did not show any obvious reasons for the low compression… take a look at the valves after the cylinder was removed:
Unless I’m missing something, I don’t see anything that would explain such a low compression number. The cylinder has been shipped to Tim Barnes at Skyline Cylinders for repair, so I’m hoping he will be able to give me more information about it. You can listen to the audio for more thoughts about this whole experience, and maybe I’ll give an update on it in a future episode.
I also mentioned in this episode my latest project in the shop at Classic Aviation – an annual inspection on a nice E33A Bonanza:
It’s a great airplane, with a great owner – now that’s a good combination!
The post “172 – A Perplexing Low Cylinder Compression on a Piper Saratoga” appeared first at AirplaneOwnerMaintenance.com
I had a surprise call this morning… my friend Eddie called and wondered if he could borrow a borescope. One of the cylinders in his Sonex’s Jabiru engine had zero compression, and he wanted to take a look inside the cylinder, especially at the exhaust valve.
Since I’m always looking for a good story, it didn’t take me long to say, “This sounds interesting… I’ll grab my borescope and drive right over to the airport.”
We got the borescope set up and quickly noticed the exhaust valve appeared to be open a tiny bit when it should have been fully closed. There was just enough leakage past the valve to keep the compression at zero.
We’re still not totally sure about that area at about the 8 o’clock position, but we didn’t see anything alarming when we looked at the valve edge with it open.
Thankfully, Eddie had done some research online and quickly got some feedback about the importance of regularly adjusting the valves in the Jabiru engine.
Sure enough, the exhaust valve had no clearance between the valve stem and the rocker arm (it should be .010)
After adjusting both valves on that cylinder, Eddie did another compression test, and we were pleasantly surprised… 70/80! And it was even a cold compression test!
It’s always great when there’s a simple solution!
Well done Eddie! And thanks for the good story we can all learn from!
In this week’s episode, we also talk about Lycoming SI 1418, a rarely used procedure for cleaning cylinders on the engine using some special equipment and ground up walnut shells.
Listen to this concept and let me know your thoughts… hit that button over to the right and tell me if you think it’s a crazy idea, or a great idea… I’m curious about it.
Reminder: I offer a service to evaluate your borescope photos. If you are not sure what your pictures mean, send them to me and I’ll evaluate them and send you a report within two days.
Josh recently purchased his 1963 Beechcraft Debonair and needed some help, so I flew to his airport and spent the good part of a day with him. We replaced a broken exhaust support angle on the right exhaust tailpipe, and then we took a good look around the airplane.
It surprised me when we discovered missing cotter pins in the left and right main landing gear uplock cable clevis bolts.
Toward the end of our time that day, we borescoped the exhaust valves, and they were all in very good condition. Here’s the exhaust valve in cylinder #1:
This is the appearance of a very healthy exhaust valve.
I flew the little Cessna 150 home and got it tied down before dark… what an adventure!
If you’d like to talk about the possibility of having me come to YOUR AIRPORT for some consulting and training on your airplane, send me an email, and we can set up a time to talk. Even if it’s across the country, I can hop on the airlines if necessary. Don’t hesitate to contact me, and we can make a plan.
Contact me at dean{at}airplaneownermaintenance{dot}com.
Final tip for today: Check your ignition switch and make sure you cannot remove the key unless it’s in the “OFF” position… watch for the condition in the following video, which is VERY DANGEROUS if the key is removed with one or both mags on, and the prop is rotated!
The post “153 – A Flying and Maintenance Adventure at Ravenswood WV” appeared first on AirplaneOwnerMaintenance.com
Yesterday, I had an opportunity to present a talk at our local IA renewal seminar about exhaust valve borescoping.
I shared some of my favorite pictures – the ones that demonstrate how critically important borescoping is, and that compression testing alone is not sufficient.
The following three examples are especially startling, since they showed a compression test of at least 60/80, but were in imminent danger of in-flight failure:
The FIRST ONEis from a Continental engine in an A36 Bonanza. Notice the green area at 9:00, indicating that area was in danger of a piece breaking off the edge.
The SECOND ONEis from another Continental engine, also an A36 Bonanza. The compression of this one was 61/80, but there was a chunk missing from the edge, with a crack toward the center of the valve!
The broken edge still had enough area to seal for a compression test:
And the THIRD ONE was from a Lycoming engine in a Cessna 152. Take a look:
In the previous three examples, the borescope was absolutely necessary to discover these dangerous and unairworthy exhaust valves.
For comparison purposes, the following two pictures are examples of healthy exhaust valves:
I also shared some pictures of valves that other people have removed from their engines.
The following is from Sylvan Martin’s Grumman Tiger with a Lycoming O-360 engine. Sylvan was able to land safely after his engine ran slightly rough. He said, “My opinion is that cylinder 1 would have been noticeable at a minimum of 150 hrs before it deteriorated to the point of cracking that far across the face… Compression check will help w/ ring problems, but our family’s experience in industrial diesels (power generation) is that rings fail slowly/predictably while valves fail suddenly/catastrophically…..”
He later had to change two other cylinders, after the borescope indicated they were burning:
(Previous three photos courtesy of Sylvan Martin.)
Jason Figueroa had to change a cylinder on his Cherokee 235’s Lycoming O-540 engine due to a burning exhaust valve that was found with a borescope.
(Photo courtesy of Jason Figueroa.)
Jason said, “Borescoping told us we had an impending problem, and led to catching it before it failed.”
Here are two more exhast valve pictures from an unidentified source:
I’m convinced this broken valve could have been detected with a borescope LONG BEFORE the edge broke off.
My hope is that all of us who have the responsibility of determining the airworthiness of piston engines in airplanes, will use a borescope along with the compression tester for higher levels of safety and reliability.
Do you have a dream to fly? If so, you might be encouraged by the poem I shared at the end of my talk yesterday. My daughter sent it to me one day last Summer… it’s called, “The Dream Does Not Die!” If you’re interested, be sure to listen to the last part of the audio.
During the recent annual inspection on Drew Wright’s Cessna 182, cylinder #1 had a low compression of 42/80. However, with the amazing technology of borescoping, he was able to take a look inside the cylinder. The nice concentric circle of deposits on the face of the exhaust valve indicates a healthy valve. Drew wondered if perhaps this valve would be a good candidate for lapping in place, without removing the cylinder.
Even though the valve appeared healthy, Drew noticed a significant amount of air leaking out the exhaust during the compression test. Once again, his borescope was very helpful in observing the condition of the exhaust valve and seat area. The valve looks good, except for the rough and uneven seating area.
The seat also looks good, except for the corresponding rough and uneven seating area.
With the supervision of his A&P, Drew was able to remove the rocker cover and the exhaust valve springs. After verifying the valve guide was in good condition with no excessive wear, and the valve was sliding freely in the valve guide, he was ready to “lap” the valve (to apply a small amount of valve grinding compound to the edge of the valve using a long Q-tip through the top spark plug hole, and spinning the valve against the seat to smooth out and improve the seating area.)
Drew used a piece of wood dowel rod, some clear tubing, and some hose clamps, for this task… I like his idea so much, I’m planning to use this technique in the future.
One of the most important parts of the lapping process, is cleaning out the residue after the job is finished. One method is to spray Av-gas into the top spark plug hole to wash the grinding compound off the valve and the surrounding areas, and let it run out the bottom spark plug hole. Multiple washings, along with some compressed air, cleans up the area very well.
An additional thing Drew did was to push a thin cloth into the top spark plug hole, and pull the valve back to squeeze the cloth between the valve and valve seat. Then, he could turn the valve against the cloth and clean the seating area even better. I’m also going to keep that little tip in mind for my next lapping project. Thanks Drew!
The seating area of the valve showed a nice smooth band after the lapping was done – very impressive!
After the lapping was completed, a new rotator was installed on the exhaust valve, everything was reassembled, and the compression immediately improved!
But the best result was the compression test that was done after running the engine… that same cylinder that was 42/80, now had a compression of 78/80! What a fantastic result, and now, hopefully that cylinder will run reliably for many more hours.
Be sure to listen to the audio for this episode for more details about Drew’s adventure. He also shared about an induction leak that was visible because of some blue fuel staining.
After removing the intake pipe, it was obvious the gasket had shifted out of position during the assembly process many years ago… perhaps this was part of the poor idling problem that was also corrected during the annual inspection. After installing a new intake gasket and adjusting the idle mixture setting, the engine idled much better than before.
Drew’s story is a true inspiration in so many ways.
So, if you, as an airplane owner, have an interest in learning and getting involved in the maintenance, just find an A&P who is willing to give you some supervision to keep things legal, and you’ll have all kinds of possibilities.
Well done Drew, on your exhaust valve lapping project! I’m thrilled with the result you achieved on this one!
Drew has a young family, and it makes me happy to know he’s taking such good care of his airplane… after all, he’s got some precious cargo to haul around!
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