Is this a scratch or a crack?

[FlyBoyM20J]

I have a shiny new borsecope and a shiny overhauled cylinder (see my recent thread about C2 and the bent pushrod), so at the 10-hour break-in oil change today, I decided to scope C2.  I should note that the new EV on C2 has been sticking on descents once in a while and, as mentioned in that prior thread, was leaking on compression test when we first did the cylinder install (we staked it and it behaved properly after that).

So, when I borsecoped C2 just now, after almost 10 hours of flying at 25 square, I was half ready to see a problem...and was certain that what I saw was a cracked valve!  My A&P is skeptical but we are both unsure at this point what we are looking at.  Did I scratch this thing with the borsecope itself somehow?

If this is just me being paranoid and stupid, then my plan is to rope-trick this valve with my A&P to deal with the stuck-on-descent thing...which is so odd since the EGT trace is perfectly calm and nothing else seems wrong.  But I do not want to pull the cylinder again if all it takes to set things right is reaming the guide and cleaning the stem.

 

[alextstone]

43 minutes ago, FlyBoyM20J said:

I have a shiny new borsecope and a shiny overhauled cylinder (see my recent thread about C2 and the bent pushrod), so at the 10-hour break-in oil change today, I decided to scope C2.  I should note that the new EV on C2 has been sticking on descents once in a while and, as mentioned in that prior thread, was leaking on compression test when we first did the cylinder install (we staked it and it behaved properly after that).

So, when I borsecoped C2 just now, after almost 10 hours of flying at 25 square, I was half ready to see a problem...and was certain that what I saw was a cracked valve!  My A&P is skeptical but we are both unsure at this point what we are looking at.  Did I scratch this thing with the borsecope itself somehow?

If this is just me being paranoid and stupid, then my plan is to rope-trick this valve with my A&P to deal with the stuck-on-descent thing...which is so odd since the EGT trace is perfectly calm and nothing else seems wrong.  But I do not want to pull the cylinder again if all it takes to set things right is reaming the guide and cleaning the stem.

 

I'm no mechanic but my money is on a scratch.

[carusoam]

You mentioned bent push rod...

What bent it?

did the piston meet the valve?

The valve is showing a nice pizza image.

That gunk is probably what got scratched...

send cleaner on stick in there and see if it washes off...

expect that the steel (?) valve is harder than the dental camera... unlikely to get scratched by the camera and a light touch...

Then Scope again..

Pp thoughts only,

not a mechanic,

-a-

[Hector]

That does not look like a crack. Scratch most likely.


Sent from my iPad using Tapatalk

[Cody Stallings]

Cracks in most all cases need a right angel to propagate from. I would say a scratch or the propriety coating(if it has any) starting to come off of the valve.

I would wanna look at the other side of that valve just to verify, cause the side we are seeing will have a compression layer on it, the other side will be the stressed side. Pull it out an have it Mag Checked(Magnafluxed). 

[FlyBoyM20J]

5 hours ago, Cody Stallings said:

Cracks in most all cases need a right angel to propagate from. I would say a scratch or the propriety coating(if it has any) starting to come off of the valve.

I would wanna look at the other side of that valve just to verify, cause the side we are seeing will have a compression layer on it, the other side will be the stressed side. Pull it out an have it Mag Checked(Magnafluxed). 

This was a reconditioned ("serviceable") valve that the cylinder overhaulers chose to install instead of a new one.  Is it a bad thing if it loses some or all of its coating?

Here's what it looked like when I received the cylinder back from Jewell last week.  I didn't get any pictures from the port side.

[FlyBoyM20J]

5 hours ago, carusoam said:

You mentioned bent push rod...

What bent it?

did the piston meet the valve?

The valve is showing a nice pizza image.

That gunk is probably what got scratched...

send cleaner on stick in there and see if it washes off...

expect that the steel (?) valve is harder than the dental camera... unlikely to get scratched by the camera and a light touch...

Then Scope again..

Pp thoughts only,

not a mechanic,

-a-

This is the cylinder after it was overhauled by Jewell.  So, this particular valve train didn't get messed up...yet.  This cylinder has a total of 10 hours on it, all ROP at 25 square, for break-in.  So that's the way the pizza image developed in just a few hours.

The story about the old valve and the bent pushrod is over here: 

 

[Yetti]

scratch.   You can see on one end of it where a little ball of metal is balled up.   Also cracks are generally a jagged line.  These are straight lines.    Same thing in nature.  When looking for people made things look for the straight lines.   Nature is mostly jagged lines.   Works for spotting airports also.

[FlyBoyM20J]

Great...I am probably paranoid after the last few weeks that started off with a bunch of oil on the port side of fuselage and wing, followed by the discovery of the bent pushrod, cylinder removal, shipping to Jewell for overhaul, re-installation, needing to stake the *just overhauled* EV to get decent compressions, 10 hours of break-in, ready to believe anything can happen.

Cliff

[carusoam]

 

They say paranoia is good for airplane ownership...  

 

Glad we connected the two threads back together...

How do the JPI EGT graphs look lately?

Did the saw tooth patterns all clear up? 

Best regards,

-a-

[FlyBoyM20J]

Here's a JPI graph from the 2nd or 3rd break-in flight, 1.5 hours going in circles (more like a rhombus) in the local practice area at 3500 MSL, 25 square.  Green is the cylinder that had to be overhauled.  As you can see, the C2 EGT trace is very calm but I still get a minor stuck valve almost every descent. 

Here I've zommed in on the descent:

 

[Runway37]

Can we see the probe end of the scope please.

[Pete M]

I'd wanna know what scratched it. 

[Shadrach]

On 5/25/2019 at 6:08 AM, FlyBoyM20J said:

This was a reconditioned ("serviceable") valve that the cylinder overhaulers chose to install instead of a new one.  Is it a bad thing if it loses some or all of its coating?

Here's what it looked like when I received the cylinder back from Jewell last week.  I didn't get any pictures from the port side.

Highly probable that it’s just the reflection and lighting, but that cylinder hone does not look like it has much of a cross hatch.

 

They certaily appear to be scratches. There appears to be “swarf” at the end of each scratch.

 

 

Edited May 28, 2019 by Shadrach

[FlyBoyM20J]

On 5/26/2019 at 8:42 AM, Runway37 said:

Can we see the probe end of the scope please.

Here's the end of the scope.  I'm now assuming that I scratched it when I pulled the control to articulate the probe tip back to look around in there since when I look at the earlier pictures there are fewer scratches.  Looks like I must have scratched it when I first looked at it (new meaning to changing things by observation), then was alarmed, scoped all the other cylinders (without scratching anything), then came back and somehow managed to scratch this first EV again.

 

Here's the first picture when I thought I had a cracked valve...so, wow, this valve surface is easily scratched?

 

[Runway37]

I've never used one but am surprised that it could scratch the valve like that. Looks like a brass or bronze small "inner" ring at the very end. Is the black rim just visible under the blue stuff steel?

[ArtVandelay]

Aluminum is pretty soft.


Tom

[Shadrach]

7 hours ago, ArtVandelay said:

Aluminum is pretty soft.


Tom

valves are not made of aluminum. They are made of steel. The scratch is most likely in the deposits that are coating the valve face not the steel face itself.

Edited May 27, 2019 by Shadrach

[FlyBoyM20J]

12 minutes ago, Shadrach said:

valves are not made of aluminum. They are made of steel. The scratch is like mostly in the deposits that are coating the valve face not the steel face itself.

This is turning into my assumption since whatever I did with the borescope, it didn't involve much force. And I scoped all the other cylinders.  Here are pictures of C4, C1, and C3...can anyone spot any more scratches?  These will probably have much, much thicker deposits on them than C2's EV which has only 10 hours on it since overhaul.

C4

 

C1

 

C3 (2 pictures)

And the plugs after I cleaned them by picking out lead deposits and using mineral spirits with an old toothbrush on the electrode area.  Then blown with compressed air.  I just ordered a spark plug cleaning kit from ATS, along with a gap checker.  Some of these look like they need blasting in this picture and I'm definitely getting some left-mag, right-mag rough running during the inflight mag check.

[carusoam]

Great pics and graphs, Flyboy!

Thanks for supplying the details.

Show an inflight mag check from the JPI when able...

a good vertical shot of the plugs may reveal how worn they are... the center electrode wears in a football pattern...

PP thoughts only, not a mechanic...

Best regards,

-a-

[FlyBoyM20J]

This is the first portion of yesterday's 1.3 hour flight.  It shows the lean runup mag check and the LOP inflight mag check.  I added some annotations in GIMP.

Cliff

[carusoam]

Great annotations, Flyboy.

Interesting variation between L and R mags.  Looks similar to some difference in mag timing...

 

And an extra special word of the day entry by Ross...  defining the scratch, vs. crack...

https://en.m.wikipedia.org/wiki/Swarf

If there is swarf at the end... It is going to be a scratch that left it there...

Best regards,

-a-

[Cyril Gibb]

On 5/24/2019 at 10:31 PM, FlyBoyM20J said:

I have a shiny new borsecope and a shiny overhauled cylinder (see my recent thread about C2 and the bent pushrod), so at the 10-hour break-in oil change today, I decided to scope C2.  I should note that the new EV on C2 has been sticking on descents once in a while and, as mentioned in that prior thread, was leaking on compression test when we first did the cylinder install (we staked it and it behaved properly after that)

I’m not sure why there aren’t any comments about your experience with your newly overhauled cylinder.  I think it’s pretty unusual that staking the exhaust valve should be necessary after an overhaul.  Perhaps some overhaul detritus remaining that fell in to the valve seat?  Could whatever that was cause the scratch on the subsequent startup?  And have you asked Jewel about the overhauled cylinder having a sticking exhaust valve?  That doesn’t sound right.

The recommendation for breaking in is running the engine hard.  Lycoming recommends 75% to prevent cylinder glazing.  25 squared at 3500 feet sounds a bit light. 

[FlyBoyM20J]

13 hours ago, Cyril Gibb said:

I’m not sure why there aren’t any comments about your experience with your newly overhauled cylinder.  I think it’s pretty unusual that staking the exhaust valve should be necessary after an overhaul.  Perhaps some overhaul detritus remaining that fell in to the valve seat?  Could whatever that was cause the scratch on the subsequent startup?  And have you asked Jewel about the overhauled cylinder having a sticking exhaust valve?  That doesn’t sound right.

The recommendation for breaking in is running the engine hard.  Lycoming recommends 75% to prevent cylinder glazing.  25 squared at 3500 feet sounds a bit light. 

Thanks, Cyril.  This is a fair question.

I don't like to think that Jewell did a bad job on this cylinder overhaul.  Rather, I assume that my A&P or I did something to introduce a particle of debris into the valve guide or seat during our fuel-based leak check prior to assembly, or during the assembly itself. 

If you look at the C2 EGT trace in some of the JPI graphs I have shared, C2's EV is not sticky at any stage of flight (no sawtooth waveform, no instability that isn't shared with the other cylinders' EGT traces indicating a system state change). 

But it does have the occasional "stuck" behavior on descent.  This might be consistent with the theory of a small deposit on the stem or guide.  So I think, at any rate - this is my first time working this kind of problem, so all of my assumptions are questionable.

I will probably call David Jewell and discuss my findings with him after I take another compression reading one day this week.  I would like to get his thoughts on what I am seeing.

That said, it seems straightforward to "rope trick" this valve to inspect the guide, stem, and seat.  I'll ream the guide and clean the rest and reassemble.  This cylinder is at the front of the engine and easy to access.  This is all less bother than removing the cylinder to send back to Jewell or somewhere else.  I'm just waiting for my valve spring compressor and guide reamer to arrive.

Relative to break-in at 75% power, I'm no expert but it seems to me that 2500 RPM @ 25 inches at 3500 MSL seems about right, if not excessive per the table in the IO-360 operator's manual.  Perhaps I'm misinterpreting it, though.  This really is my first time dealing with cylinder work and break-ins.

Thanks,

Cliff

 

 

[Shadrach]

On 5/27/2019 at 8:56 AM, FlyBoyM20J said:

This is the first portion of yesterday's 1.3 hour flight.  It shows the lean runup mag check and the LOP inflight mag check.  I added some annotations in GIMP.

Cliff

Take off is not notated in the graph but it looks to me like take off EGTs (mid to high 1100s) suggest excellent fuel delivery at full power and full rich. 

I think the reason folks asked about 25 squared is because it’s well understood that there’s no benefit to reducing throttle unless you’re trying to go down or slow down. The term and the setting is kind of a relic from when we had little to no engine instrumentation. 

I’ve broken in one set of Cylinders LOP and will likely do any future cylinders the same way if operationally possible. Cool CHTS and high mean ICPs make for optimal results. It can be done on either side of the mixture spectrum but it’s cleaner and more efficient going lean.

Your cylinder is likely broken in by now. If you think about what is actually occurring during the process (sharp peaks from the hone process being blunted to a smooth, consistent surface with valleys to hold oil on the cylinder wall) it seems crazy that some claim tens of hours to achieve break in. I’d love to see some data on why/if that actually happens.

Edited May 28, 2019 by Shadrach