valves, borescopes, and cylinder rescue

[Marc_B]

Did a very quick/brief search to see if this was recently discussed...but read the Jan issue of AOPA Pilot about borescopes, low compressions, and valve lapping. 

https://www.aopa.org/news-and-media/all-news/2022/january/pilot/savvy-maintenance-cylinder-rescue

https://resources.savvyaviation.com/wp-content/uploads/savvy_pdf/exhaust-valve-lapping-paul-new.pdf

Great info that prompted me to venture further down the rabbit hole of learning.  After a lot of reading I came across this video that I thought was just really informative for the non-mechanic pilot!

I found it interesting about the rotocoils/rotator caps and this definitely gave me another thing to keep an eye on at annual and with maintenance moving forward.  I found it well worth the time to watch.

[carusoam]

This is where we discuss a good pizza vs. a not so good pizza….  

Sticky valves don’t rotate like they should…. Then they suffer from hot spots… the valve image changes quickly…

The nice pizza image turns not so nice…. Irregular.

There are some low cost bore scopes for about 20 bucks…. Lighted, with various options…

PP thoughts only,

-a-

[Marc_B]

Question to the gurus...what parameters on your engine monitor data would you look for to suggestion time or profitability for valve lapping? Or is this based on asymmetric appearance of borescope, low compression of cylinder?  I suspect that increased EGT in a single cylinder would be a late finding?  Paul New mentions, "If performed too early, it’s just an extra unnecessary expense. If performed too late, it’s ineffective and a total waste of time."  What defines the right time???

 

[carusoam]

Engine monitors first pick up sticky valves… showing a saw tooth pattern…. Of the EGTs…

Any owner reviewing monitor details will see it… graphs, not while flying….

When you see saw tooth patterns…. The the borescope gets called in… looking for pizza/no pizza…

Then mechanic then gives guidance on next steps based on what his eyes see….

PP thoughts only, not a guru…

-a-

[PT20J]

Lycoming and Continental have very different exhaust valve designs. Lycoming's sodium filled valves will take more heat but the stems run cooler and deposits build up and cause them to stick according to Ed Krollin https://aslcamguard.com/sticking-exhaust-valves/. Continental's  valves won't take as much heat (that's why Continental has a lower CHT redline than Lycoming) and burn more easily unless they rotate and the rotocoils seem to wear after a few hundred hours. Lot's of threads about this on Beechtalk. 

Skip

[201Steve]

I think prior to lapping, if stickiness is suspected, reaming the guide would be a reasonable first step, assuming compressions hold. Morning sickness would be a surefire bet. Left unattended, heating and gunk likely lead to an unhappy mating surface. 

[EricJ]

1 hour ago, Marc_B said:

Question to the gurus...what parameters on your engine monitor data would you look for to suggestion time or profitability for valve lapping? Or is this based on asymmetric appearance of borescope, low compression of cylinder?  I suspect that increased EGT in a single cylinder would be a late finding?  Paul New mentions, "If performed too early, it’s just an extra unnecessary expense. If performed too late, it’s ineffective and a total waste of time."  What defines the right time???

 

Download the monitor data and look for an oscillation of EGT on any cylinder.   If there is a significant temperature oscillation with a period of a couple minutes or so, it is evidence of a burning valve.   As it rotates and the burned valve and seat interference line up the EGT goes up.   This is one of the behaviors that Savvy's engine analysis looks for automatically.

[201Mooniac]

2 hours ago, carusoam said:

There are some low cost bore scopes for about 20 bucks…. Lighted, with various options…
 

Are there low cost borescopes that are really useful for this type of inspection?  The low cost ones I've seen aren't articulating, just flexible.  If you know of a low cost one that is useful for this type of inspection I'd appreciate a pointer.

[PT20J]

8 minutes ago, 201Mooniac said:

Are there low cost borescopes that are really useful for this type of inspection?  The low cost ones I've seen aren't articulating, just flexible.  If you know of a low cost one that is useful for this type of inspection I'd appreciate a pointer.

Vividia has several. Seems to be the most popular low cost scope maker. http://www.vividia-tech.com/

[201Mooniac]

14 minutes ago, PT20J said:

Vividia has several. Seems to be the most popular low cost scope maker. http://www.vividia-tech.com/

I agree those seem like they will do the job but Anthony mentioned $20 and the ones I've seen at that price point are just flexible "snake" type units and do not have articulation control.  The Vividia VA-400 seems a reasonable one but still 10x the $20 I was hoping was true.

[carusoam]

1 hour ago, 201Mooniac said:

I agree those seem like they will do the job but Anthony mentioned $20 and the ones I've seen at that price point are just flexible "snake" type units and do not have articulation control.  The Vividia VA-400 seems a reasonable one but still 10x the $20 I was hoping was true.

my bad!

I had a car engine problem the other day… and bought the $20 snake version 

it has a mirror that goes on the end and might fit down a plug’s hole…

Trying to aim it at the outside of the engine was challenging enough….

Might be good for inspecting inside a cowl for pre-flight….   

Amazon Prime had it on a one day sale….

Best regards,

-a-

https://smile.amazon.com/NIDAGE-Automotive-Inspection-Semi-Rigid-Smartphones/dp/B07C9C6P5D/?_encoding=UTF8&pd_rd_w=TSulF&pf_rd_p=72148aa9-8c08-440b-8d2e-6a79acee3ae3&pf_rd_r=SY473TQCK8KG0308GGVB&pd_rd_r=0bb02b14-dc23-42f6-9693-c0efdfdcf05b&pd_rd_wg=NH5mN&ref_=pd_gw_ci_mcx_mr_hp_atf_m

[Boilermonkey]

And then the mirror falls off in the cylinder when using the cheap ones.  Ask me how I know!

[Hank]

6 minutes ago, Boilermonkey said:

And then the mirror falls off in the cylinder when using the cheap ones.  Ask me how I know!

Remember, there's inexpensive, then cheap, then cheap Chinese junk!

[EricJ]

3 hours ago, Hank said:

Remember, there's inexpensive, then cheap, then cheap Chinese junk!

I'm told the Russians have a saying:  Cheap man pays twice.

[haymak3r]

DANG! That is a great video! Question though.. At around 26 minutes. The valve guide slop... Pretty normal and he can see that after 200hours?!?!?! I've torn down auto engines with 200k miles, and have never seen valves that loose in their guides. Are the materials that outdated on these engines?? As engines are overhauled, are newer materials being used to prevent this? That's a bit scary to see lol.

[201Mooniac]

10 hours ago, carusoam said:

my bad!

I had a car engine problem the other day… and bought the $20 snake version 

it has a mirror that goes on the end and might fit down a plug’s hole…

Trying to aim it at the outside of the engine was challenging enough….

Might be good for inspecting inside a cowl for pre-flight….   

Amazon Prime had it on a one day sale….

Best regards,

-a-

https://smile.amazon.com/NIDAGE-Automotive-Inspection-Semi-Rigid-Smartphones/dp/B07C9C6P5D/?_encoding=UTF8&pd_rd_w=TSulF&pf_rd_p=72148aa9-8c08-440b-8d2e-6a79acee3ae3&pf_rd_r=SY473TQCK8KG0308GGVB&pd_rd_r=0bb02b14-dc23-42f6-9693-c0efdfdcf05b&pd_rd_wg=NH5mN&ref_=pd_gw_ci_mcx_mr_hp_atf_m

No worries, I was just hoping you were right and there was a $20 choice

[Yetti]

15 hours ago, 201Steve said:

I think prior to lapping, if stickiness is suspected, reaming the guide would be a reasonable first step, assuming compressions hold. Morning sickness would be a surefire bet. Left unattended, heating and gunk likely lead to an unhappy mating surface. 

Nothing more fun that watching the mechanic take a steel punch and large ball peen hammer and wacking away to get the valve out.

[Yetti]

13 hours ago, 201Mooniac said:

I agree those seem like they will do the job but Anthony mentioned $20 and the ones I've seen at that price point are just flexible "snake" type units and do not have articulation control.  The Vividia VA-400 seems a reasonable one but still 10x the $20 I was hoping was true.

You can always double back the camera on the cord and tape the cord together.

[larryb]

I have the Vivida. The first time there was a learning curve, but now I can get pics of all 6 cylinders in about half an hour. And the first time I used it in my Encore I did find a burnt exhaust valve. I sent the pics off to my shop for a second opinion and he agreed it was a burnt valve.  So I had the cylinder replaced with new. While I wasn't happy about having to replace the cylinder, I was quite happy that I was able to have the work done at my home shop on my schedule vs. a potential catastrophic failure far from home. The engine was running fine, although the cylinder with the burnt valve was also the cylinder with the lowest compression at the previous annual. 

 

I also stuck it up the exhaust pipe to get pics of the turbo wheel.

 

I went with a new cylinder because of turn around time. I don't mind fixing problems with the plane, but I really hate having it sit there for weeks on end waiting on something. I was able to order the cylinder and have it in hand when I took the plane in for the work. My plan was to have the removed cylinder overhauled and keep it as a spare. But then I asked the shop how much cylinder overhauls typically cost and he said they rarely come in for less than $1500. Since new was $1700 I didn't see much value in the overhaul.

 

Larry

[EricJ]

21 hours ago, Marc_B said:

Did a very quick/brief search to see if this was recently discussed...but read the Jan issue of AOPA Pilot about borescopes, low compressions, and valve lapping. 

https://www.aopa.org/news-and-media/all-news/2022/january/pilot/savvy-maintenance-cylinder-rescue

https://resources.savvyaviation.com/wp-content/uploads/savvy_pdf/exhaust-valve-lapping-paul-new.pdf

Great info that prompted me to venture further down the rabbit hole of learning.  After a lot of reading I came across this video that I thought was just really informative for the non-mechanic pilot!

I found it interesting about the rotocoils/rotator caps and this definitely gave me another thing to keep an eye on at annual and with maintenance moving forward.  I found it well worth the time to watch.

+1 that this is a vid worth watching if you do any of this monitoring or work yourself.    Very informative.

I have the semi-rigid Vividia scope and recommend it if you want to use it for things beyond cylinders.   For example, since it snakes around things I sent it up my exhaust to inspect the muffler interior, flame tube, etc., which you couldn't do with the straight version.   Also, my understanding is that they're coming out with a higher-res version if they haven't already.   It'd be worth making sure you get the newer one.

I also have various versions of the cheapie USB endoscopes from Amazon or wherever, and some of them are great and some not so much.   None of them will make cylinder inspection as easy as the Vividia with the articulating end.    There are more expensive scopes available, too, that articulate multiple directions, have their own screen, etc, but the Vividia is very good bang for the buck.