Borescoping Engines

[kontiki]

I jsut read a pretty convincing article on compression testing vs borescope in EAA Sport Pilot.

According to the author, borescopes are cheap enough that it's reasonable to expect the local shop/AMT to accomplish one on a prebuy.

Is that the case? I'd love to have a look at the valves before buying.

 

[JB1842]

If this is like the last thread on borescoping.....

 

[Silvaire]

I'll say my piece and the usual suspects can tell you how I'm full of it and don't know what I'm talking about but here it is:

First of all this is NOT a borescope

Secondly, even if you were to use a real borescope (which would cost on average around $3k without an articulating probe and at least $10k with one) by the time you can visibly see something wrong with your valve your compression reading is going to be ZERO.

Personally I own two "scopes" The first is a ProVision PV 300 Fiberoptic Scope and the second is a Dewalt DCT411S1 and they are great tools for getting a serial number off of a hard to see magneto dataplate or for looking under the floorboards or inside a wing. Both of them will easily fit through a spark plug hole and with the clip on mirror you can look at the valves.

But the bottom line is, you're not going to look in a cylinder that has perfectly good compression readings and go "WOW, look at the big chunk burned out of that exhaust valve!" It just plain ain't gonna happen.

In fact you may have a cylinder with absolutely dismal compression readings that can't be fixed by any of the usual methods and when you pull it and look down there with the noonday sun at your back it's very likely that your naked eye will fail you and you won't be able to spot a single, visible thing wrong with it.

There, I've said it and I'm not going to say anymore.

 

[Goofy]

Oh crap, here we go again.....small time a&p forum troll vs. A guy that manages a few million dollars of aircraft.

Choose your advice carefully.

 

[Goofy]

There, I've said it and I'm not going to say anymore.

If only we could be so lucky.....
Usual suspect.

 

[Henning]

I'll say my piece and the usual suspects can tell you how I'm full of it and don't know what I'm talking about but here it is:

First of all this is NOT a borescope

Secondly, even if you were to use a real borescope (which would cost on average around $3k without an articulating probe and at least $10k with one) by the time you can visibly see something wrong with your valve your compression reading is going to be ZERO.

Personally I own two "scopes" The first is a ProVision PV 300 Fiberoptic Scope and the second is a Dewalt DCT411S1 and they are great tools for getting a serial number off of a hard to see magneto dataplate or for looking under the floorboards or inside a wing. Both of them will easily fit through a spark plug hole and with the clip on mirror you can look at the valves.

But the bottom line is, you're not going to look in a cylinder that has perfectly good compression readings and go "WOW, look at the big chunk burned out of that exhaust valve!" It just plain ain't gonna happen.

In fact you may have a cylinder with absolutely dismal compression readings that can't be fixed by any of the usual methods and when you pull it and look down there with the noonday sun at your back it's very likely that your naked eye will fail you and you won't be able to spot a single, visible thing wrong with it.

There, I've said it and I'm not going to say anymore.

Not true at all. I can tell you when a valve is about to have a problem by looking at the coloration pattern on the face before you'll even notice it on the compression test or hear it in the exhaust pipe. Soon enough in fact that you could lap the valve in situ and fix the problem before it becomes an expensive repair. I don't need a $3000 borescope, all I need is something that fits in the spark plug hole and allows me to view the exhaust valve face.

 

[Frank]

Could we have a buyers' guide to borescopes? What works best for the money?

 

[kontiki]

All,

The article I refer to in the OP was in the July 2013 eddition of EAA Sport Aviation Magazine.

 

[N175PT]

Could we have a buyers' guide to borescopes? What works best for the money?

Over on VAF is a thread on using $87 dental cameras off Ebay. Haven't done it yet myself but a friend has and I've seen the pics/videos. As mentioned you can very clearly see the color pattern around the circumference of the valve head and if its not even all the way around then you have a problem developing.
What's very nice about it is if the guide is worn you can actually see the valve slip sideways as it seats, I've see that video also from another guy. I was hoping it was on utube but I could not find it.
I'd much rather have a good look around inside than a leak down test, it has its place but can give false readings.
Especially if comparing results year by year given by different equipment on different days by different people at different temperatures.
Yeah I know it's required....
Tim

 

[poadeleted20]

I'm not understanding how one can speak of borescoping versus compression testing. That's like asking about a colonoscopy versus a pulmonary function test -- different tests which identify different issues. You want a complete picture of health (engine or body), you need both.

 

[Tom-D]

I'm not understanding how one can speak of borescoping versus compression testing. That's like asking about a colonoscopy versus a pulmonary function test -- different tests which identify different issues. You want a complete picture of health (engine or body), you need both.

No Ron, It is more like having colon/rectal problems, and seeing why with a colonoscopy.

If there is nothing wrong, you see nothing out of the ordinary.

 

[tmyers]

If this is like the last thread on borescoping.....

You gonna share some of that popcorn Crash?

 

[JB1842]

You gonna share some of that popcorn Crash?

I popped 3 bags. Help yourself!

 

[poadeleted20]

No Ron, It is more like having colon/rectal problems, and seeing why with a colonoscopy.

If there is nothing wrong, you see nothing out of the ordinary.

Point taken, but either way, it's not an exclusive "either/or" choice. Weak compression may lead you to do a borescope, but so may other things, and weak compression alone may lead to other diagnostics than a borescope inspection.

 

[tsts4]

Point taken, but either way, it's not an exclusive "either/or" choice. Weak compression may lead you to do a borescope, but so may other things, and weak compression alone may lead to other diagnostics than a borescope inspection.

Exactly and Mike Busch isn't advocating it be an either/or choice. In fact the title of the article is "Compression in Context". Here's a link for those who'd like to read it in full: http://www.sportaviationonline.org/sportaviation/july_2013/?pg=36&pm=2&u1=friend

And here's the link to the video that Tim was referring to over on VAF that was made using an $87 Chinese made dental cam:

http://youtu.be/Dq0H_yqSuGw

 

[N175PT]

That's not the one I was refering to but thanks. In that video you can actually watch the valve closing, and just as the valve head ends it travel you can see it slide sideways...a frightening mount. And it's the side loading the valve gets hit with that will eventually fail the stem. It was a very good catch by whoever it was. Probably saved an off field landing.
Tim

 

[Henning]

Point taken, but either way, it's not an exclusive "either/or" choice. Weak compression may lead you to do a borescope, but so may other things, and weak compression alone may lead to other diagnostics than a borescope inspection.

Why wait for weak compression to look with a borescope? By the time you have weak compression and you hear it coming out the exhaust, your 'cheap fix' option is gone.

 

[Geico266]

Not true at all. I can tell you when a valve is about to have a problem by looking at the coloration pattern on the face before you'll even notice it on the compression test or hear it in the exhaust pipe. Soon enough in fact that you could lap the valve in situ and fix the problem before it becomes an expensive repair. I don't need a $3000 borescope, all I need is something that fits in the spark plug hole and allows me to view the exhaust valve face.

It is amazing what this man knows.

When are you going to be within 500 miles of Lincoln? I'm buyin!

 

[taters]

My dads dental boroscope works great...if you know a dentist ask to borrow.

 

[gismo]

Over on VAF is a thread on using $87 dental cameras off Ebay. Haven't done it yet myself but a friend has and I've seen the pics/videos. As mentioned you can very clearly see the color pattern around the circumference of the valve head and if its not even all the way around then you have a problem developing.
What's very nice about it is if the guide is worn you can actually see the valve slip sideways as it seats, I've see that video also from another guy. I was hoping it was on utube but I could not find it.
I'd much rather have a good look around inside than a leak down test, it has its place but can give false readings.
Especially if comparing results year by year given by different equipment on different days by different people at different temperatures.
Yeah I know it's required....
Tim

I have one of the dental cameras and it works pretty well. I did have to perform some "surgery" on the neck to get it to fit in the plug hole with enough clearance to position it for viewing the valves. I've tried a fiberoptic scope and found the image quality to be far inferior to the dental cam. A good prisim based borescope can deliver good images but the least expensive one worth considering costs several hundred bucks and a really good one can be many times that.

Here's a picture of one of my valves taken with the dental camera.

 

[Silvaire]

Closing arguments

I have one of the dental cameras and it works pretty well. I did have to perform some "surgery" on the neck to get it to fit in the plug hole with enough clearance to position it for viewing the valves. I've tried a fiberoptic scope and found the image quality to be far inferior to the dental cam. A good prisim based borescope can deliver good images but the least expensive one worth considering costs several hundred bucks and a really good one can be many times that.

Here's a picture of one of my valves taken with the dental camera.

I agree with you gismo, despite their low cost the dental cameras are much better for this application. The video inspection cameras and fiber optic scopes do a good job of looking straight ahead but when you put the mirror on the head the LED's wash the image out. I've had some luck with external illumination through the opposite spark plug hole but it's not as good as the dental cams.

However this still doesn't alter my position on the subject. Henning will tell us that he can detect by subtle coloration patterns that a valve is destined to fail and that he can prevent that from happening. I'm not going to say he can't but I want a show of hands from owners:

Compression test is 78/80, engine runs fine. Henning or Mike Busch or your A&P pokes an $87 Chinese dental camera in your spark plug hole and says he sees some coloration anomaly. Are you going to let him do an in-situ valve lap, pull the jug or in any other way shape or form mess with your cylinder?

You've all seen the dramatic footage of the wobbling valve. Trace it back to the source on Beech Talk. You'll discover that that cylinder in the video had 1500 hours on it. You're looking at classic valve guide wear - not something that is sensationally abnormal.

There is a reason that we use dial indicators with an accuracy of one thousandth's of an inch when working on these things. As remarkable as the Mark One Eyeball is it can't see this stuff. Those remarkable photos in Mike Busch's webnars (that are from TCM's service bulletin) not one of them was taken through a borescope. They are all pictures of cylinders that had been removed because the compression test showed 0/80.

I don't mean to offend anyone, I'm just expressing my opinion on this subject and I've got plenty of experience. I don't appreciate people like Goofy attacking me and calling me a two bit internet troll just because my opinion is different. If you don't like it, if you don't agree that's perfectly fine with me but for cripes sakes don't call me names or disparage me. That's total BS.

 

[gismo]

Re: Closing arguments

I agree with you gismo, despite their low cost the dental cameras are much better for this application. The video inspection cameras and fiber optic scopes do a good job of looking straight ahead but when you put the mirror on the head the LED's wash the image out. I've had some luck with external illumination through the opposite spark plug hole but it's not as good as the dental cams.

However this still doesn't alter my position on the subject. Henning will tell us that he can detect by subtle coloration patterns that a valve is destined to fail and that he can prevent that from happening. I'm not going to say he can't but I want a show of hands from owners:

Compression test is 78/80, engine runs fine. Henning or Mike Busch or your A&P pokes an $87 Chinese dental camera in your spark plug hole and says he sees some coloration anomaly. Are you going to let him do an in-situ valve lap, pull the jug or in any other way shape or form mess with your cylinder?

If I was planning on a lengthy trip in the not too distant future and I found an exhaust valve with the classic signature of distress (very asymmetrical coloring) I'd seriously consider having the cylinder repaired even if the compression was 79/80. But if not, I'd probably fly another 10 hours and check it again to see how fast it was progressing. It's pretty clear to me that it is possible to detect impending valve trouble but it's far less clear whether this is infallible at detecting valve problems before they affect performance, a viable replacement for compression checks, or just another useful tool.

You've all seen the dramatic footage of the wobbling valve. Trace it back to the source on Beech Talk. You'll discover that that cylinder in the video had 1500 hours on it. You're looking at classic valve guide wear - not something that is sensationally abnormal.

On that subject I'm even more confused. Watching videos of my own valves going up and down, it looks to me that even on a relatively low time engine the valves appear to move laterally a bit when seating. This may be an illusion or it might simply be "normal" behavior that has been going on in our engines far longer than we think and only recently appears to be problematic due to the availability of the cameras.

I do know that TCM strongly supports the idea of borescoped valve inspection periodically and I suspect they have or are accumulating data that supports that position.

 

[Silvaire]

Re: Closing arguments

...On that subject I'm even more confused. Watching videos of my own valves going up and down, it looks to me that even on a relatively low time engine the valves appear to move laterally a bit when seating.

Asymmetric valve guide wear in pushrod engines is an inevitability unless you are using roller rockers because the end of the rocker arm moves in an arc and exerts a lateral force on the valve stem as it pushes it open. When that wear becomes visible to the naked eye I don't know but the wear begins the first time you start the motor.

I do know that TCM strongly supports the idea of borescoped valve inspection periodically and I suspect they have or are accumulating data that supports that position.

On this my opinion is that TCM had a problem with their original maintenance standards which allowed zero leakage through the valves when performing a standard differential compression test. This is the subject that Mike Busch's article covered and in that article he implied that perfectly good cylinders were being replaced for no good reason. I'm sure there were, and still are cases of this happening but in the real world, at least in part 91 ops, virtually nobody was abiding by those TCM standards. When a cylinder compression reading was low, which is not uncommon for big bore Continentals, all of the normal methods would be pursued prior to cylinder removal. That would usually include running the engine, possibly staking the valves and I'm sure a quart or two of Marvel Mystery Oil got snuck in there every once in awhile too.

When Continental issued SB03-3 I believe it was an attempt to adjust their own standards to align better with what was actually going on out in the field. This was the first time they had mentioned borescopes and under the section titled Burned Valves that can be seen by borescope inspection the first line states that they usually result in a differential compression test reading in the range of 0/80 to 40/80. Contrary to Mike Busch's claim that borescope inspections should become the gold standard and that compression tests should take a back seat, TCM says nothing of the sort.

What they say is basically this (Table 1 in SB03-3)

Do a compression test
If it fails and leakage is through exhaust valve do a borescope inspection
If it looks normal through the borescope then fly at cruise power for at least 45 minutes and repeat the compression test
If it still fails the compression test pull the cylinder

So you see TCM is telling you to pull the cylinder despite the fact that it looks perfectly okay through a borescope.

I don't know why some people get so wound up when I tell them this. they can read SB03-3 themselves, it's right there in plain black and white English.

 

[Tom-D]

Re: Closing arguments

On that subject I'm even more confused. Watching videos of my own valves going up and down, it looks to me that even on a relatively low time engine the valves appear to move laterally a bit when seating.

do the valve wobble check see what you really have. there is a service bulletin on that too.

 

[Frank]

Exactly and Mike Busch isn't advocating it be an either/or choice. In fact the title of the article is "Compression in Context". Here's a link for those who'd like to read it in full: http://www.sportaviationonline.org/sportaviation/july_2013/?pg=36&pm=2&u1=friend

And here's the link to the video that Tim was referring to over on VAF that was made using an $87 Chinese made dental cam:

http://youtu.be/Dq0H_yqSuGw

I watched the Mike Busch video, and after watching it I am pretty sure that if I saw asymmetric green coloring on an exhaust valve, I would pull the cylinder. The probability it is a bad exhaust valve appears to me to exceed 50%, or more, and the consequences of having an exhaust failure in flight seem to be a lot more than twice as costly as pulling a cylinder. The expected cost of pulling a cylinder (around $1,500) seems to be less than the expected cost of an in flight failure (50% times $20,000 or more).

The cost of the tool seems irrelevant. It is the result of the inspection that seems to make a difference.

 

[Henning]

Re: Closing arguments

However this still doesn't alter my position on the subject. Henning will tell us that he can detect by subtle coloration patterns that a valve is destined to fail and that he can prevent that from happening. I'm not going to say he can't but I want a show of hands from owners:

Compression test is 78/80, engine runs fine. Henning or Mike Busch or your A&P pokes an $87 Chinese dental camera in your spark plug hole and says he sees some coloration anomaly. Are you going to let him do an in-situ valve lap, pull the jug or in any other way shape or form mess with your cylinder?

Lets see a show of hands, good idea. You have no compression problem currently. I put a picture of your carbon crusted valve up on the screen that has a dark side on an oblong pattern. I explain that this is caused by a layer of carbon that is insulating the valve seating surface from transferring heat to the seat and head there. I explain that these carbon deposits are what cause burnt valves and that if the situation is not addressed you will be changing a jug in the not too distant future. I explain that as there is not yet any critical damage, I can very likely remedy the issue by pulling the exhaust off that cylinder and the rocker and valve spring from that valve, attach a drill motor to it and dab some lapping compound I blend up from carbon remover and oxalic acid crystals and clean up the situation in a couple hours of labor and $25 in materials restoring the seating surface.

So, faced with this, do you spend $200?

 

[Goofy]

Quote:
Originally Posted by Silvaire;1227825l

There, I've said it and I'm not going to say anymore

See, we weren't so lucky....

Usual suspect.

 

[Silvaire]

Re: Closing arguments

Lets see a show of hands, good idea. You have no compression problem currently. I put a picture of your carbon crusted valve up on the screen that has a dark side on an oblong pattern....

That's swell Henning, it really is but in my world this isn't happening and I don't know of anyone else who is experiencing this. In fact, in my world it seems exactly the opposite is happening because usually it is the compression test that fails yet there is no visible anomaly on the valve face such as you describe. Furthermore the machine shop verifies that the valve is leaking and fixes it.

But you describe it as though you see this all the time, that you've done your in-situ drill lap routine enough times to definitively tell us that without that routine that valve would have failed and because of your action it didn't. That's a tough allegation to prove given the whole nature of the future that didn't happen and all. I'm not saying it ain't so but I remain skeptical.

 

[Silvaire]

See, we weren't so lucky....

Who's "we"? Your the only one who has an issue with this discussion to which you, btw never contribute anything. Is someone forcing you to read my posts against your will? Because if there is let me know and I'll have a stop put to it.

 

[Tom-D]

In every case when I do the rope trick and remove the carbon from the guide and valve stem, the valve will fail the allowable wobble that Lycoming gives in their SB.

when it is worn out, it is worn out, hard concept to understand for some.

 

[N747JB]

My dads dental boroscope works great...if you know a dentist ask to borrow.

You do wash it off before you give it back, right?

 

[Goofy]

Who's "we"? Your the only one who has an issue with this discussion to which you, btw never contribute anything. Is someone forcing you to read my posts against your will? Because if there is let me know and I'll have a stop put to it.

And you are simply not a man of your word. Just a factual observation. Go on, insult me some more....

 

[Sailer]

I am an owner who found a bad exhaust valve during a plug change. Used a $60 dental oral camera. I have taken Mike Bush's two day course. That's how I knew to look and what to look for. Check the video and see if you can tell why it's bad.

http://m.youtube.com/watch?v=YGjTAa9jsPc&desktop_uri=/watch?v=YGjTAa9jsPc

BTW, while servicing the cylinder the shop insisted the cylinder had a crack. I had to purchase a new one, but asked for the old one back. After every known test, no crack found. If anyone tells you a cylinder has a crack, make them prove it with a definitive dye pen test.

 

[NoHeat]

Check the video and see if you can tell why it's bad.

The exhaust valve does not have the same coloration all the way around its perimeter. It is burned on the right side, as seen in the images.

Is that right?

If you have an engine monitor, I bet it showed an oscillating EGT for that cylinder.

 

[Sailer]

The exhaust valve does not have the same coloration all the way around its perimeter. It is burned on the right side, as seen in the images.

Is that right?

If you have an engine monitor, I bet it showed an oscillating EGT for that cylinder.

You would think it would show up in the EGT, but it didn't. But those images are about as clear as you can get that the valve was getting ready to go. Mike Busch gave it another 20 hours or so. Anything that is not symmetric around the entire face is suspect. In this case it was very clear. At the time the cylinder had about 1820 Hobbs hrs. On it. That was an original cylinder on the plane. All of the other cylinders looked fine.

 

[Silvaire]

I am an owner who found a bad exhaust valve during a plug change. Used a $60 dental oral camera...

What was the compression reading on that cylinder?

 

[Sailer]

What was the compression reading on that cylinder?

Never took one. I was changing plugs when I found it. My annual had been scheduled for a few weeks after, so I just moved it up. We pulled the cylinder based on the condition of the exhaust valve with the intention of simply repairing it. But as I mentioned, the crack issue surfaced to change all of that.

Everyone that saw the images agreed the exhaust valve was bad and had to go.

Edit-- just checked and we did check compression on #5. It was 0. Annual the prior year had 62/80.

Oil sample just prior to my finding the problem was showing higher nickel and insolubles. They were suspecting an exhaust valve but were not ready to call it.

 

[Sailer]

Not wanting to hijack the thread, but one other important bit of information. As I was changing the plugs I did a cylinder flush using a mixture of Seafoam and 100L fuel. This has nothing to do with the exhaust valve, but my compressions on an 1820 hr engine were 71 / 70 / 70 / 65 / 0 / 64 . Since I have owned the plane it would not hold more than 6 quarts of oil with 8 as full. And in a 50 hr run would use 5-6 quarts of oil.

Now it holds 8 and on the last 45 hour oil run used only 3 quarts.

I have since learned there are more gentle additives than Seafoam, but the engine flush is something every owner should consider at every plug change or 500 hrs. I made sure the mixture did not stay in the engine long at all. And it will eat up an oil change in the process as the oil must be discarded after running for an hour or so. Others may have different results, but it sure worked in my engine.

I will not give specifics about the process as I don't want to have that responsibility. But check around about the process.