Thoughts?
Worth trying to lap in place? I've never lapped a valve but reading about it, doesn't seem like too big a deal.
Worth trying to lap in place? I've never lapped a valve but reading about it, doesn't seem like too big a deal.
The first and only indication of an issue was the look of the thing from borescoping during condition inspection, particularly the classic asymmetric heat pattern and perhaps a hint of green.I would 100% attempt to lap this, but first I would want to understand the failure. -
What is the Leak-down, and did it change suddenly or slowly? What are your operating conditions? Do you have an engine monitor, and has the data changed?
Vividia Ablescope VA-400.Outstanding photos, which borescope are you using?
I think it's lead deposits, not carbon.
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That is carbon build up/deposits. certainly worth a try, but may be difficult to remove via lapping compound. You will likely need to do it multiple times until you are at the point of a smooth steel surface with all of the raised carbon deposits gone. Looks like the deposits are almost .010" in height. I would start with the coarse compound and finish off with fine once the deposits have been removed. The compound breaks down pretty quickly, so will need to keep applying fresh paste. Lapping is normally done just to make parts mate. Here you are using it to remove a good amount of hard material. Carbon deposits like that are very hard and stick better than glue. Think about a diamond. Take carbon, add a lot of heat and pressure and you get a diamond. Here you have 1500+ degrees and at least 200 PSI. What it produces won't be a diamond, but will be darn hard.
What causes these carbon deposits?
I’d love to hear how you made out! The exhaust valve seats on my O320-E2D look exactly like yours. A white, alligator skin-like deposit. What is the stuff?? I can’t seem to find a definitive explanation. Some BeechTalk guys think its lead bromide but I run unleaded auto fuel. The RV guys think it’s carbon. But isn’t carbon black in colour??
As an aside, I also realized (d'oh!) that the "economy cruise" that I've been flying a lot also keeps CHTs way down and not hot enough to properly scavenge lead and other buildups. So the "bad" news is I really should start going faster
19.5"MP / 2350 RPM / 5500' / OAT 57. Coolest (#1) 300, hottest (#4) 340.What CHT's do you see in economy cruise, and what RPM, MAP and at what altitude?
Just curious, thanks.
... the Lyc just looks like a simple cap that fits over the end of the valve stem to protect the stem from wear! So how does it make the valve rotate...or does it!
What about valve rotation - or lack thereof? Does this engine have the Rotator Valve Stem Caps installed? As I understand it, they are meant to cause the valve to rotate in service - keeping the valve/seat interface cleaner.
How they actually cause rotation is a mystery to me....and everyone I ask. Does anyone know?
The Continental rotator cap is a whole different animal...and I can understand how they work, but the Lyc just looks like a simple cap that fits over the end of the valve stem to protect the stem from wear! So how does it make the valve rotate...or does it!
OK, I'm quoting myself...but everyone is missing the point of the question:
Does the valve rotator cap on a Lycoming do what the name implies - that is, does it CAUSE the valve to rotate, or does it simply ALLOW the valve to rotate.
Update: Latest borescope image, about 30 hrs after lapping. I also sent this to Savvy (with whom I have a QA subscription) and their response was:
I think the valve looks great. It can take up to 50 hours for the face to even out, so I'm not worried at all. Rotation + good compression will keep this valve happy. (posted here with permission)
I must say that this thread is hitting a lot of very important topics for our lycoming engines, comps, wobble specs, exhaust valve pics and rotation. spread the word to all your friends that this is crucial for a healthy running engine! beside this info 'morning sickness' is a tell that a stuck valve is coming soon. I know of a rv that went down recently and the pilot was unaware of this stuff. I'm sure this is probably what happen. thanks for this post . I would also include yearly oil change, coarse screen check, oil filter cut open for inspection, oil analysis and proper leaning below %75 power and flying the *rap out of it on a regular basis.
Thanks. Did my best with a long Q-tip and solvent.The lapping compound wasn't cleaned off very well looking at the photo. It ends up turning into crusty material that stays on the edge of the valve like it did here. Use a big Q-tip soaked in solvent to clean while spinning the valve.
Does the valve rotator cap on a Lycoming do what the name implies - that is, does it CAUSE the valve to rotate, or does it simply ALLOW the valve to rotate.
It only allows rotation. A careful look at dimensions shows that the rotator cap sits on the valve keepers, not on the top of the valve stem. I recall the nominal spacing between rotator cap and the top of the stem is about .004 inches.
When the rocker arm actuates the valve, the first movement is the rotator cap slightly releasing the keepers, thus allowing rotation. Only then does it start to move the valve itself. What causes rotation? The rotating exhaust stream passing by the valve. Why does it rotate? For the same reason that water flowing out of a sink rotates -- Coriolis force is my guess.
FYI, it is not called a rotator cap. It is called a "valve stem cap." Seems everyone here calls it a rotator cap, leading everyone to believe that its purpose is to cause rotation. But Lyc doesn't call it that.
Why does it rotate? For the same reason that water flowing out of a sink rotates -- Coriolis force is my guess.
Just a tiny bit each time but measured over many bonks it incrementally rotates in one direction. I don't know the mechanism myself but I suspect it's a designed-in side-effect of the spring.
EDIT: Come to think of it, I believe I took that pic after lapping but before cleaning.Thanks. Did my best with a long Q-tip and solvent.
This what Lycoming calls it on the IO-360-M1B, from the Parts Catalog:
"CAP, Valve stem, exhaust (rotator type)"
It is quite possible that there are different caps in use. Possibly some use the cap to create rotation and some do not. The 320 parts catalog that I referenced for that post did NOT state rotator type.