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Engine issue -opinions requested

E

Ejshields

I'm New Here
Second flight into phase 1 testing of my RV 9A and the engine developed a miss and partial power, requiring a hurry up landing. Removing the valve covers, the exhaust valve on #3 looked very different (see picture). A grey coating in the oil covering the valve.

Engine has 1400 hrs flown in a flight school and is an O-320, D2B.
Any suggestions regarding the grey material on the valve?

Bore scoping tomorrow and a compression check after.

Thanks
IMG_4667.jpeg
 
Do you have any electronic engine monitor logs showing the EGTs for each cylinder?
A sticky valve is one possible cause, but confirming that would require further inspection, including borescope examination and other appropriate checks.
 
Ejshields said:
Second flight into phase 1 testing of my RV 9A and the engine developed a miss and partial power, requiring a hurry up landing. Removing the valve covers, the exhaust valve on #3 looked very different (see picture). A grey coating in the oil covering the valve.

Engine has 1400 hrs flown in a flight school and is an O-320, D2B.
Any suggestions regarding the grey material on the valve?

Bore scoping tomorrow and a compression check after.

Thanks
View attachment 121505
Click to expand...
Is that a crack I see on the rocker on the right side (exhaust valve)? Or maybe something else?
 
@dhmoose Has Eagle-eye-Xray vision -- Sure looks like a crack in the exhaust lifter.

Lycoming Part # 74636

Off topic - a bit. I sure hope the rest of the airframe wasn't constructed like the baffles...
 
I agree the potential crack on the rocker arm needs further investigation and replacement but I don't see that as the cause of the problem. Clearly exhaust gas is getting past the valve guide. Most likely stuck or damaged valve. Leak down check and a borescope should give you a solid idea.

One issue I had on a Beaver I used to fly for work, the engine used to run abnormally hot and the mechanics at the time couldn't figure out why. However the cylinders would run so hot for so long the exhaust valve seat would get rammed up into the overheated aluminum cylinder head, to the point the valve would no longer seat and would loose compression. Do you have the rubber baffle seals removed in this picture for some reason? How was your CHT? I really don't think this would be the issue as it would take longer than one flight. Just a data point.
 
Top of engine is sealed with a plenum with the sealing material on the plenum. Baffle is tightly bolted to the plenum resulting in a very tight seal. Using a johnson cowl. CHT on #3 gets high on climb out but quickly reduces below 400 in level flight and comes in line with other cylinder temps.

This is a 1400 hr engine and perhaps this valve issue is a carry over issue from previous use.

Borescope will happen tomorrow with a leakdown ck to follow
 
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Looks like the exhaust rocker is cracked and that grey sludge is fine metallic debris, likely related to the cracked rocker. Will likely find a great deal of wear on the rocker shaft and part of the rocker bushing missing. As it wears away the oil takes the debris away and deposits on the retainer. The crack was likely from a stuck valve event and mechanic wasn’t observant enough to catch it and just reinstalled it; sad, but typical. Usually the pushrod will yield and bend before the rocker breaks, but not always.

Note that they grey starts right at the crack and goes down from gravity.
 
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