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Would you lap the valve or monitor?

I would run another 25-50 hrs, which every makes you comfortable. You can to pull through every once in a while (safely) to be sure, but if it was trouble brewing the outer rim would be showing more heat and burn off the deposits.

Does your engine have valve rotators? That might be a preemptive repair, but without a leak, it would not be indicated . . . . yet. 2-cents
 
Valve lapping only helps cases of lo compression.
Not dramatic yet, but there’s a trend… I’d check for the rotator cap, and free movement of the valve in its guide, as in SB388C.
 
What Dan said. Also, any previous photos that could tell you if the valve is actually rotating?
 
78/80 I could hear a very slight amount of air getting into the exhaust until I moved the prop just a bit, then it went away.

If it goes away when you rotate the prop a little then most likely you were not at TDC. 78 is not a bad number at all. If the valve was truly leaking you would be seeing numbers well below that. I would just fly it. Check it again at the next oil change and make sure you are at TDC when you do.
 
Need a response from an engine builder

I'm not that guy; however, common sense (to me) would indicate a different problem. From what I saw in the pix, the valve/seat alignment looks off versus just being miss-ground. I cannot conceive of a way this can happen without a valve stem/guide issue. I personally would inspect for this and correct as required. You could very well be on the way to a stuck valve or a broken stem. Please keep us informed.

Hopefully an experienced engine builder will respond.
 
Thanks for the responses so far guys. I don't have the same exact view but here is a pic taken from what appears to be the other spark plug hole at 100 hours. The light spot does appear to be rotated about 45 degrees if you compare to the intake valve.

S20210804_0064 by Jereme Carne, on Flickr
 
Thanks for the responses so far guys. I don't have the same exact view but here is a pic taken from what appears to be the other spark plug hole at 100 hours. The light spot does appear to be rotated about 45 degrees if you compare to the intake valve.

S20210804_0064 by Jereme Carne, on Flickr

I agree that the most likely issues is in the guide area and not likely resolved witl lapping. Lapping is a finishing process and is not likely to repair a poor valve grind and will certainly not resolve issues with the guide. Same way that honing won't fix shape irregularities in a cylinder; that requires boring.

While the heat pattern shows a less than perfect sealing arrangement between seat and valve, I would not necessarilly expect it to result in early failure, though monitoring is advised. 78/80 indicates that the valve is sealing well. Heat marks indicate that the contact area (seat to valve) is smaller in the vicinity of those marks than the other areas. Also possible that the valve is not rotating and that is the reason for the assymetrical heat signature. If it were rotating, you wouldn't notice that one area had a smaller contact patch. A closer examination of the contact marks on the valve and seat would indicate more. You can pull the spring, drop the valve an inch and then can get better pics of what is going on if your concerned.

Larry
 
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Thanks for the replies guys. I also reached out to Aerosport and Lycoming and they both agreed to just keep flying it and to monitor any changes, they didn’t sound very worried at all at this point.

I’ll keep an eye on it at each oil change. I like Larry’s idea as a first step if it gets worse.
 
2nd pictures posted are way less „dramatic“ than the first ones… a perpendicular view of the valve’s head with good lighting sure help in assessing the heat pattern.
 
That's certainly a sign of a problem - but it's not that big a sign (yet). This is like your child is running a fever of 99.5 - you keep an eye on it, but don't call the doctor yet.
 
Okay it would appear after talking to you guys and Lycoming that it is actually quite possible that the valve is not rotating properly. Anything that can be done about this? It's my understanding that they are not like Continnentals were there is a dedicated rotator device. Just trying to get a future plan ready for when the time comes.
 
I have fixed a number of cylinders with valves not rotating both on big bore Continentals and Lycomings by lapping the valve, replacing the rotator cap, and making a few quick passes in the guide with a ball hone. In most cases the discoloration was a lot more severe and lopsided. Checking at the next annual revealed better compression and a more even "burnt pizza" look to the valve face. It does work and I consider it good preventative maintenance as the cylinders age. I would not do it in this case as the valve interface still appears to be in good shape.
 
I have fixed a number of cylinders with valves not rotating both on big bore Continentals and Lycomings by lapping the valve, replacing the rotator cap, and making a few quick passes in the guide with a ball hone. In most cases the discoloration was a lot more severe and lopsided. Checking at the next annual revealed better compression and a more even "burnt pizza" look to the valve face. It does work and I consider it good preventative maintenance as the cylinders age. I would not do it in this case as the valve interface still appears to be in good shape.

Thanks Bob for posting! I agree that it doesn't need addressed right now after hearing from others with more experience than myself but I would like to be ready when it does. I was thinking of tracking down a reamer and ball hone at some point anyways just in case as I like to fly and don't want to be grounded awhile waiting for one. I can also start up some conversations with my A&P buddies in the meantime; see what kind of beverage they prefer. :)
 
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