J

jimkwalton

Active Member
Cruising along at 6,500 MSL, 23 inches, 22 RPM, lean of peak at 8 GPH when all of a sudden the engine starts buzzing, partial power loss! Change tanks, mixture full rich, boost pump on. No change.

Look at #4 EGT has dropped to 400° and going down. CHT starts dropping. I still have control of the engine just partial loss of power.

Stayed high, landed at destination since it was next to closest airport.
Also as I entered the pattern (high of course) the engine power returned to normal.

Downloaded flight data. It showed #4 cylinder EGT/CHT drop for 6 minutes then return to normal. Buzzing sound from engine.

Side note, this happened to #2 cylinder about 3-4 months ago for less than a minute.

Stuck exhaust valve? Debris in fuel line?

IO-390 in my RV14 around 380 tach time from new engine. Cold engine start has a short “morning sickness” on start until. I aggressively lean after start.

Any thoughts?
 
Stuck valves typically present first when cold, but this is not universal. I would not expect exh valves to release themselves if they stick when hot. usually they first stick when cold and as the cyl warms up, the guide grows a bit, then un stick. If they stick at full opeating temp, there is no real mechanism for them to un stick. I would be looking at injector clogging first. Always good to do a wobble test, so not recommending against that.

Sorry, missed the part about morning sickness. However, if you can make the synptoms go away by leaning, IMHO it is not morning sickness. The only thing that makes it go away is heat that opens up the valve guide.
 
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Maybe something else...

Zoom out a bit and look at the EGT trend for the minute or so before "event." What does the EGT look like?
 
Roll dice, or known fix?

turbo said:
time to run full diagnostics. leave nothing unturned.
Click to expand...

Indeed . . . . could be either valve or fuel event. A good look at the data will greatly help to sort the possibilities. If one does not start with a definitive theory based on the data, then there is little (or no way) confidence in knowing the issue is fixed.

EDIT: Based on reading your OP a few times, sticky exhaust valves would be a likely candidate, and with your hours, others experience and the SB, it would not be a waste to proceed with the reaming of all 4 guides. In doing the pre reaming tests, it is pretty clear when they are tight and a good indicator that you will have addressed the root cause.
 
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Sticky valve and LOP?

Okay I had a new one sprung on me yesterday. If you’ve been following my other thread about loss of power and flat EGT, we’ve discussed fuel flow issues (I removed and cleaned fuel injectors yesterday) and possible exhaust valve sticking.

A mechanic friend said it’s obvious that it’s a sticky valve because I run the engine LOP all the time, not allowing fuel to lubricate the valve!

I was kinda dumb struck on his comment. I have never heard any issues due to LOP mixture control during cruise!!! Now he says it’s the lead in the fuel that lubricated the exhaust valve!!!?!

Am I the ignorant one here? Which I admit that could be the case……
 
jimkwalton said:
Okay I had a new one sprung on me yesterday. If you’ve been following my other thread about loss of power and flat EGT, we’ve discussed fuel flow issues (I removed and cleaned fuel injectors yesterday) and possible exhaust valve sticking.

A mechanic friend said it’s obvious that it’s a sticky valve because I run the engine LOP all the time, not allowing fuel to lubricate the valve!

I was kinda dumb struck on his comment. I have never heard any issues due to LOP mixture control during cruise!!! Now he says it’s the lead in the fuel that lubricated the exhaust valve!!!?!

Am I the ignorant one here? Which I admit that could be the case……
Click to expand...

mechanic is clueless. LOP operation DOES NOT cause sticky valves (lots of theories out there but no conclusive answer) and only an incompetent mechanic would believe that fuel lubricates an exhaust valve guide. Lead does cover the face of the valve and seat and this lead does lubricate their interface. Pushrods send oil to the rocker box and this oil lubricates the valve stem/guide interace. Only takes an hour (with necessary tools) to figure this out. Pull the rocker cover, pull the exh rocker, pull the spring, then see if the valve is tight. If EGTs went instantly from normal to ambient, then I feel that fuel delivery is not likely and the valve is more likely.
 
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Graphs

See if you can read my graphs on the photos
 

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jimkwalton said:
See if you can read my graphs on the photos
Click to expand...

See attached screen grab -- login to Savvy, load the flight in question, click the icon circled in RED -- then come to this site, post a reply to this thread and press "CTRL-V" (windows) or "COMMAND-V" (mac) to paste the link...

In any case, I do see a little spike on EGT #4 right before it goes south -- this is what a clogged injector looks like; the clog isn't 100% so the jug starts to go lean for a bit, then the clog goes to 100% and the fire goes out -- EGT drops to 0, CHT follows suit.
 

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Where?

bjdecker said:
See attached screen grab -- login to Savvy, load the flight in question, click the icon circled in RED -- then come to this site, post a reply to this thread and press "CTRL-V" (windows) or "COMMAND-V" (mac) to paste the link...

In any case, I do see a little spike on EGT #4 right before it goes south -- this is what a clogged injector looks like; the clog isn't 100% so the jug starts to go lean for a bit, then the clog goes to 100% and the fire goes out -- EGT drops to 0, CHT follows suit.
Click to expand...

Sorry, I do not see the screen you have on the right.
 
LIttle spike

bjdecker said:
See attached screen grab -- login to Savvy, load the flight in question, click the icon circled in RED -- then come to this site, post a reply to this thread and press "CTRL-V" (windows) or "COMMAND-V" (mac) to paste the link...

In any case, I do see a little spike on EGT #4 right before it goes south -- this is what a clogged injector looks like; the clog isn't 100% so the jug starts to go lean for a bit, then the clog goes to 100% and the fire goes out -- EGT drops to 0, CHT follows suit.
Click to expand...

Yes, I see that little spike. Thanks. I don't want to pull valve covers and takes things apart if not needed.

I still don't see how to share the link. sorry.
 
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bjdecker said:
See attached screen grab -- login to Savvy, load the flight in question, click the icon circled in RED -- then come to this site, post a reply to this thread and press "CTRL-V" (windows) or "COMMAND-V" (mac) to paste the link...

In any case, I do see a little spike on EGT #4 right before it goes south -- this is what a clogged injector looks like; the clog isn't 100% so the jug starts to go lean for a bit, then the clog goes to 100% and the fire goes out -- EGT drops to 0, CHT follows suit.
Click to expand...

I would agree, the chart shows a relatively typical clogged injector and matches my initial speculation. A 10 minute fix with acetone and a toothpick. One caution is that this could be a one off or an initial indication of a larger debris issue. I would pull the finger strainer and look at the debris load.
 
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Bent pushrod

So here’s the latest on my “flat cylinder” drama. I have flown the plane 5 hours since the #4 cylinder went “flat” in flight for 6 minutes.

I pulled the #4 rocker cover and rockers off today. I have a very bent pushrod and pushrod tube. The reason I removed all this was due to an oil leak that developed in the pushrod tubes after my event (along with a distinct tapping I could now hear after the event).

I will try to attach a photo of the rod here. In the second photo you can see a metal cap that was just laying below the exhaust valve rocker.
 

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Excuse me if I’m too blunt but why in the world would you continue to fly after the event without finding the cause? Valve tapping after the event and you flew 5 more hours? It was recommended by many to check for a tight valve!
I’m sorry, but this is a perfect recipe for a disaster!
Now, please don’t just change the pushrod and cover. Fix the sticking valve!!!!
 
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CAP, Valve stem, exhaust

I know next to nothing about Lycoming engines, so in the interest of "education" I started googling...

Page 22 of this (page 36 in the pdf) Item #11
https://www.lycoming.com/sites/default/files/attachments/PC-IO-390-D%20Series.pdf

Page 23 says "Item 11 17C19386 CAP, Valve stem, exhaust "

Found a photo of that part number.
https://pilotshq.com/products/lycoming-cap-valve-stemexhaust-17c19386

Sure looks like what is in your photo.

I learned something new today!

Now as to how that ended up there...

Makes me wonder to myself, Would it have come free after the pushrod got bent, or would it have caused the pushrod to bend?

Googling some more, according to this, it seems like it could come free after the valve get stuck.
https://www.avweb.com/ownership/dealing-with-stuck-valves/

Chuck
 
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Thank you

KMMUflyer said:
I know next to nothing about Lycoming engines, so in the interest of "education" I started googling...

Page 22 of this (page 36 in the pdf) Item #11
https://www.lycoming.com/sites/default/files/attachments/PC-IO-390-D%20Series.pdf

Page 23 says "Item 11 17C19386 CAP, Valve stem, exhaust "

Found a photo of that part number.
https://pilotshq.com/products/lycoming-cap-valve-stemexhaust-17c19386

Sure looks like what is in your photo.

I learned something new today!

Now as to how that ended up there...

Makes me wonder to myself, Would it have come free after the pushrod got bent, or would it have caused the pushrod to bend?

Googling some more, according to this, it seems like it could come free after the valve get stuck.
https://www.avweb.com/ownership/dealing-with-stuck-valves/

Chuck
Click to expand...

I appreciate your little bit of research and thought into this (instead of just ridiculing me). There were no other indications of anything amiss and I did clean the fuel injectors so it wasn’t like I was being obtuse to my issues. And it developed full power. Even my downloaded data showed nothing wrong for the last 5 hours.

But alas the oil leak led me to the bent rod and tube. I’ll be getting it fixed and service bulletins followed before it flies again.
 
Jim-
I'm sorry you're having to deal with this engine problem but I'm glad you shared it with us. I've learned from it. Keep us posted on the repair and I hope you get back in the air soon.
 
Thank you.

Jim,

Thank you for sharing this -- too often threads like this are abandoned and we loose the opportunity to learn anything useful.

It looks like perhaps you had two valve sticking events -- the first was transitioning from closed to open which resulted in the bent push rod, the second was transitioning from open to closed, which because of the now bent push rod, allowed enough clearance for the rotator cap to come off the valve stem.

The usual "spike" in EGT followed by the crash to "0" is there in the data *but* looking more closely, the EGT never does drop below 500°F. So that would indicate that the three things needed for combustion (Fuel, Air, Spark) are present, just not at a high enough pressure (exhaust valve stuck open) for normal engine operation.

Glad that nothing worse happened. Looking forward to a report on your experience performing the SI.

B
 
Jim, thanks for posting your issue. And thanks to Chuck for the great sleuthing! I learned something from this event.
 
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