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Need to replace Cylinder 2 and muffler


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The cool thing about an engine monitor...  the sticky valves leave a good fingerprint long before they become a stuck valve...
The challenge of not having an engine monitor... the pilot might not be skilled enough to recognize the early signs of sticky valves...

Does anyone have a EM graph of a sticky valve vs stuck valve? In my experience the valve is either stuck open or it’s not.
Usually mine would stick open on startup. MMO used on flight before oil change helped with this.


Tom
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3 hours ago, bradp said:

Clarence do you recommend valve wobble tests and / or rope trick empirically at XXX hours as PM? 

I only do it when stick valves are suspected as indicated by morning sickness.  Very few customers will comply with SB388 on a regular basis.

https://www.lycoming.com/sites/default/files/Procedure to Determine Exhaust Value and Guide Condition.pdf

Clarence

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On 5/2/2019 at 4:44 AM, ArtVandelay said:


Does anyone have a EM graph of a sticky valve vs stuck valve? In my experience the valve is either stuck open or it’s not.
Usually mine would stick open on startup. MMO used on flight before oil change helped with this.


Tom

I have been looking back through my JPI logs to determine the first point at which I can see that C2 is not well.  I would say it was this 3.5-hour flight on 23 NOV 2018.

One thing I note is that "approach sickness" (sticky valve on approach) seems to occur many flight hours before "morning sickness" (sticky valve at startup) starts for this valve.  If you click and zoom in, you can see one "approach sickness" dropout for the C2 EGT trace.

image.thumb.png.347d07a816f0f8653834199a65d319a8.png

Here's  short flight for IFR approach practice on 04 JAN 2019.  Notice the C4 EGT is unstable at startup but tends to drop out on approach cooldown:

image.thumb.png.83ce255f74784b0ca7e8f5662366112f.png

By 14 FEB 2019, we start to see "morning sickness":

image.thumb.png.03315fc5b47842e68ed5cdff8b545e0d.png

Here's 20 MAR 2019:

image.thumb.png.3f84c81f9d7a0cb8e86a7806bd1fa047.png

06 APR 2019

image.thumb.png.41b22ca2ba2ed1896bfc59c0cb3f24fd.png

I looked at some of these over the winter and I really thought the "dropouts" at approach and later at startup indicated a loose thermocouple connection.  But if I view them in the context of the noisy trace for C2 EGT at cruise and later the rough starts, it should have been obvious what was happening.

I just noticed the cycling of C2 CHT.  That's important, I'm sure.  And I should mention that up until mid-April 2019, I had the EDM-700 configured for its default sample rate (about 1 sample every 6 seconds).  About 3 weeks ago, I switched it to its highest rate (3 samples/second if I recall) and that has helped me see the sawtooth pattern of C2 EGT at cruise. 

I knew something was up and was about to do some real analysis but it turns out I was already out of time.

How much warning did I really have if I'd been paying attention? 

It was about 40 hours between that first flight with noisy C2 EGT on 23 NOV 2018 and the final event that bent the rod.

It was about 20 hours between the time the JPI logs show first morning sickness and the bent rod.

As Mike Busch says, “Anyone who experiences an in-flight exhaust valve failure today just wasn’t paying attention.” This is 100% correct in my case.

Cliff

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11 hours ago, Dan at S43 said:

I don't know what circumstances lead to a bent push rod, but it seems like it must be severe.  I would like to understand what has happened here.

Would this occur only if the valve did not open for some reason?  In which case, instead of concerns about compression, you would need to check the linkage between cam and valve to see what was binding?  Failed bearing/bushing of the rocker?  The valve itself welded in its guide or stuck to the valve seat?

The OP states that contact indications on the piston face exist.   This means the exhaust valve was stuck open, correct?  This should lead to a push rod flopping around, not getting caught between the cam lobe and an immovable valve.  

-dan

What I have seen in situations like this is when the valve should be closing and pushing the push rod back down against the tappet, the valve sticks open, the push rod slips out of the rocker arm at the top of the cylinder, and the next rotation pushes the push rod against whatever it happens to be lodged against. Since the push rods are on top of the Lycoming engines, gravity should have the push rod dropping down onto the rocker arm. At 2000+ RPM, it only takes an instant to get it lodged somewhere it cannot move and bend it.

Even in this case where the piston appears to have "freed" the valve without destroying itself, once the push rod is out of the rocker arm, bad things happen quickly.

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So in reading this,  I’ve learned a lot.  The length of the old pushrod is not relevant to the new pushrod length because after the cylinder work is completed the length will likely be different due to the cylinder overhaul. Selecting the correct pushrod becomes a challenge when the cylinder overhaul shop and the engine or not at the same location. This puts the installing A&P in the position of having to have multiple pushrods available to you find the correct fit. 

Have I missed anything?

Given that the pushrod length is crucial and assuming the length is determined with the lifter collapsed I am brought back to some statements I’ve seen here regarding cam follower “lift”. I’ve seen it posited many times that cam followers contribute to the opening of the valve. It’s always been my understanding that cam followers act as a cushion only and that the lifter is fully collapsed any time the cam is providing lift. Can someone speak to that?

My push rod straightening escapades were due to a tappet nut coming loose in an old Triumph unit twin that I still ride occasionally. I’m still not sure what happened exactly but I theorize that the nut got wedged in a valve spring preventing a valve from fully opening there by bending the push rod. Straightening the rod with drill was how I got the bike home.  I see now that this procedure has little to no use outside of MacGyvering antique vehicles when broken down away from home.

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Great graphs! Gents,

 

Terminology:

1) Sticky valve... valves are designed to rotate during normal operation. This allows them to be nicely cooled in a uniform sort of way... when they stop rotating, they start misbehaving... a sticky valve doesn’t rotate uniformly...

2) Valve rotation allows for that nice pizza looking image... no rotation, an Odd non-pizza image is the result... to see the pizza image, a mechanic usually uses a dental camera sent in through a spark plug hole...

3) The JPI EGT graph picks up on the issue of a sticky valve and the line generally starts to look like a saw-toothed line instead of a nice smooth line...

4) Stuck valve... JPIs are great at some things... the stuck valve EGT drops to the bottom of the graph... because there is no compression.  Compression is required to produce the proper flame... reminder... all that fuel is still going somewhere... and is probably burning in the exhaust system...

 

5) what we learned... a sticky valve is identifiable by looking at the EGT graphs... the valve guides can be cleaned using the ‘rope trick’.

6) A stuck valve usually happens in the last few minutes of a flight... because no matter where you were going... your plan has changed to land safely... you have at most 75% hp... and a few unknowns... as PIC, you will be deciding to land straight ahead... or determine the best plan to follow...

7) during my M20C stuck valve experience... while planning to land straight ahead... we quickly determined we were producing enough power to make shallow turns and land back on the next intersecting  runway...  without an engine monitor, we had no idea what the problem was... a bearing failure, or a single cylinder not operating...lots of vibration, no smoke or oil coming out that we could tell...

Its a great experience worth discussing...

For selected details like these, there are more at the Savvy website...   inviting Paul @kortopates to join the conversation... (when / if able...)

PP thoughts only, not a mechanic...

Best regards,

-a-

 

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Minor update. 

The cylinder is with Jewell Aviation.  I called this afternoon and Sam answered.  He happened to be working on it when I called.

He said nothing was wrong except that the valve guide must've gotten some debris (or just carbon buildup) in it and that the valve stem was quite worn.  So he is going to replace both the guide and the valve and that will be all it takes.  At least, I believe he said he would replace the guide; I know he said he'd replace the valve, so maybe he's just reaming/grinding the guide.

Sam did mention that the wobble test would have revealed a problem with this valve.

Oh, and on pushrods: he said you generally get to use the same length rod that was originally there, especially when you both service the guide and replace the valve...that's where I think he must be just reaming/grinding the guide but replacing the valve.  The combination gets you back to where you started, more or less, in terms of pushrod length.

He said the cylinder itself looks very good, especially for 1450 hours.  No cracks, nothing.

He asked if I wanted new rings and suggested that I do so given the hours on this cylinder.  I agreed, and asked him to mount the piston back in the cylinder before he ships it back to me.  Sure thing, he said, and that was that.

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Thanks for sharing the update....

 

Make sure to Get some instructions for breaking in the new rings, if you haven’t done so already...

Might come with oil recommendation, MP and rpm changes vs. time...

PP thoughts only, not a mechanic...

Best regards,

-a-

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On 5/2/2019 at 10:07 AM, Shadrach said:

So in reading this,  I’ve learned a lot.  The length of the old pushrod is not relevant to the new pushrod length because after the cylinder work is completed the length will likely be different due to the cylinder overhaul. Selecting the correct pushrod becomes a challenge when the cylinder overhaul shop and the engine or not at the same location. This puts the installing A&P in the position of having to have multiple pushrods available to you find the correct fit. 

 

Ross, this is my understanding, as well.  I have ordered 3 different sizes of pushrods to have on hand when the cylinder is returned to me.

15F19957-56 (13.061")

15F19957-57 (13.088") <-- this was the size that was already in there

15F19957-58 (13.115")

These are the original Lycoming part numbers, which as per SI1060T have been superseded.  But given I have an older pushrod driving the intake valve in this cylinder (and it has no P/N stamped on it), I have opted not to risk mixing a new pushrod P/N with the intake one in case they are the same length (prohibited in the SI).

Cliff

SI1060T Push Rods.pdf

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13 minutes ago, FlyBoyM20J said:

Ross, this is my understanding, as well.  I have ordered 3 different sizes of pushrods to have on hand when the cylinder is returned to me.

15F19957-56 (13.061")

15F19957-57 (13.088") <-- this was the size that was already in there

15F19957-58 (13.115")

These are the original Lycoming part numbers, which as per SI1060T have been superseded.  But given I have an older pushrod driving the intake valve in this cylinder (and it has no P/N stamped on it), I have opted not to risk mixing a new pushrod P/N with the intake one in case they are the same length (prohibited in the SI).

Cliff

SI1060T Push Rods.pdf 428.45 kB · 0 downloads

You should still try to straighten the old one just for $hits and giggles.;)

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On 5/2/2019 at 9:07 AM, Shadrach said:

So in reading this,  I’ve learned a lot.  The length of the old pushrod is not relevant to the new pushrod length because after the cylinder work is completed the length will likely be different due to the cylinder overhaul. Selecting the correct pushrod becomes a challenge when the cylinder overhaul shop and the engine or not at the same location. This puts the installing A&P in the position of having to have multiple pushrods available to you find the correct fit.

We did a field OH of 2 cylinders. and a ream of the 2 exhaust on the other side (rope trick) but we use a honest to good spring depresser tool.  Then we ran to the 2 shops on fields to see if they had different length push rods since the two OH were not specing out.    We found that by swapping left to right it all worked out.   Which then got us to thinking if the last person got the pushrod specs right.

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1 minute ago, Yetti said:

We did a field OH of 2 cylinders. and a ream of the 2 exhaust on the other side (rope trick) but we use a honest to good spring depresser tool.  Then we ran to the 2 shops on fields to see if they had different length push rods since the two OH were not specing out.    We found that by swapping left to right it all worked out.   Which then got us to thinking if the last person got the pushrod specs right.

That is interesting.  I have rope tricked a two cylinders over the last few years but none on my IO360 which seems to be very robust with regard to the valve-train.   Both occurrences were on the same Continental O200 but different cylinders over a span of 18 months.  The aircraft was a 66 C150F that I was to begin training in but was not airworthy due to a sticky valve when I arrived for the summer.  Both of the times I participated in the procedure it was done under the supervision of an IA.  We always used a proper spring compressor.  If there's a work around for removing keepers without a compressor, I'm unaware of it.  

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Further update...the cylinder is back in my hands!  Less than $600 total for the work and return shipping.

Thanks to Sam and David Jewell for a fast and friendly turnaround on this.

My AP and I are going to install it, the muffler, and the new GAMI injectors tomorrow.  I can hardly wait to get back in the air!

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23 minutes ago, FlyBoyM20J said:

Further update...the cylinder is back in my hands!  Less than $600 total for the work and return shipping.

Thanks to Sam and David Jewell for a fast and friendly turnaround on this.

My AP and I are going to install it, the muffler, and the new GAMI injectors tomorrow.  I can hardly wait to get back in the air!

Having a working plane is a good feeling.  I really beats storing a bunch of metal aluminum parts in an expensive box that you are paying rent on and insurance on all the parts that can't make it into the air.

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Cylinder 2 installed.  Not 100% without issues - first compression check revealed the new exhaust valve was leaking terribly.  We staked it; then the only leak was around the rings into the crankcase (as expected).  After a run-up, it read 76/80, so we put everything back together and I took it for a burn-in flight early today.  1.5 hours at 25 square. 

C2 traces are in green in the JPI graph attached.  You can see the CHT drop at 08:16:49 (vertical marker) just after I leaned again for max power.  I believe this is when it sealed.  The C2 EGT trace (bold green) is beautiful.

Break-in oil is Philipx X/C 20W50.

I will do at least 1 more of these break-in flights and will change the oil at 10 hours.

GAMI injectors go on tomorrow.

It is good to be flying again.  This plane is back to 100% awesome!

image.thumb.png.6c16db845ba4dca347ac79a4bc2ff0f8.png

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Nice graph!

Stake the valve... Best I can tell... aka ‘the rope trick’... clean out the valve’s guide.

The cylinder clearly changes the heat/cool characteristic compared to the other ones...

Looks like that challenge has been solved...

 

Next up Gamis...

Will you be flying the Gamis, collecting data, then swapping them for new ones, to perfect the spread?

Or did you do that already?

What’s next?

:)

Best regards,

-a-

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4 hours ago, carusoam said:

Nice graph!

Stake the valve... Best I can tell... aka ‘the rope trick’... clean out the valve’s guide.

The cylinder clearly changes the heat/cool characteristic compared to the other ones...

Looks like that challenge has been solved...

 

Next up Gamis...

Will you be flying the Gamis, collecting data, then swapping them for new ones, to perfect the spread?

Or did you do that already?

What’s next?

:)

Best regards,

-a-

I'm going to keep a *very* close eye on JPI data to see if there is any more sticking of C2 EV, but I wonder if it was just a shipping contamination or something. 

C4's EV was, in fact, also stuck when we did the post-runup compression check of C2 that led to 76/80.  I suggested we test C4 just as a reference, and lo: C4 read back about 40/80.  No JPI graph has ever shown C4 to be stuck, but some of the EGT traces for C4 do show the sticky valve signature.

So, my A&P and I were already planning on doing the "rope trick" on C4 and will also do C2 if JPI indicates it has any further issues.  This will probably be in a few weeks.  We've had enough excitement for now and I want to collect JPI data for a while post-GAMI.

As for GAMIs, they are not yet installed.  I will do one more 1.5-hour break-in flight with the old injectors tomorrow morning, then tomorrow afternoon, my A&P and I will install the new GAMI injectors.  I'm doing all this burn-in ROP (or right at peak) so I have only my last year's history of LOP to reference post-GAMI, but so it must be.

I didn't know that I was expected to install the GAMIs, then collect data, and then potentially swap injectors...I will certainly be collecting data for every single flight and am eager to see what GAMI does for my LOP stability (it was OK with stock injectors but I often couldn't go past 20F LOP before the engine ran rough).

 

 

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Gami runs a service to fine tune things at their shop...

Doing it remotely will get you close enough with data that you can collect...

Somebody was able to balance my O’s first engine with a zero or 0.1 Gami spread...

I found that much detail to be very interesting... it would lean til shut off... not lean til rough... on an engine with 1600hrs on it...

I haven’t got the experience of having fuel injectors balanced, so I am interested in what you see...

I get the feeling that the previous owner of my plane spent a few extra hours at Gami super fine tuning the fuel injectors...

Best regards,

-a-

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  • 3 months later...
On 5/2/2019 at 5:31 AM, M20Doc said:

I only do it when stick valves are suspected as indicated by morning sickness.  Very few customers will comply with SB388 on a regular basis.

https://www.lycoming.com/sites/default/files/Procedure to Determine Exhaust Value and Guide Condition.pdf

Clarence

Hey, @M20Doc (and anyone else interested in the Lycoming Valve Guide "Wobble Test"...

 

I read SB 388C, the Lycoming 400 hr "Wobble Test" service bulletin very closely as I was planning on buying the test rig when I discovered this statement:

"400 hour intervals or earlier if valve sticking suspected until exhaust valve guides are replaced with guides made of improved material. (Refer to latest revision of Service Instruction No. 1485.)"

I then looked up Service Instruction No. 1485.  It says:

"TIME OF COMPLIANCE: Half way to recommended TBO or at 1000 hours of operation, whichever occurs first or earlier at owner’s discretion or anytime valve sticking is suspected.

\As a product improvement, Lycoming has introduced a new exhaust valve guide material with an increased chrome content for improved wear characteristics. The incorporation of this guide material has significantly reduced the amount of valve guide wear (bell-mouthing) seen by some operators of Lycoming engines. Improved exhaust valve guides were initially incorporated into some cylinder assemblies beginning in April 1996.

Since March 1, 1998, all engines, cylinder kits and spare exhaust valve guides shipped from Lycoming contain the improved material. Cylinder assemblies which incorporated the improved “Hi-Chrome” exhaust valve guides when the engine was shipped from Lycoming are identifiable by the letter “C” stamped inside a circle on the boss for the drain back fitting. The individual guides made with the improved material can be identified by a 5° chamfer at the top of the guide (See Figure 1)."

 

So, for those who are interested, it appears that if your cylinder assembly  is newer than 1998 and the guides are therefore the improved ones, the "Wobble Test" is recommended every 1000 hrs instead of every 400 hrs....

Alex

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A&P's look at me like I'm crazy when I bring up SB388. Maybe they are afraid of maintenance-induced failure. Who does this regularly and how much does it cost? There is not much information about average costs for this inspection out there on the internets.

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