Cylinder #3 scoring, normal wear or something else? Dental cam pics.

[Zero4Zulu]

If your pistons have a oil scraper ring on the bottom of the piston skirt, check which direction the large chamfer is oriented. I had to rebuild my O235 because the chamfer on that ring was installed incorrectly causing dry cylinders. I know the Lycoming manual instructs the rings to be one way for the O235 and the other way for the O320.

[Noah]

Originally Posted by erich weaver

Amen!

Anyone who has played with the mixture knob and is capable of LOP knows that temps go DOWN when you lean past peak. Common sense says to lean rapidly from ROP to LOP to eliminate/minimize the time with peak temps. Me thinks John Deakin and Mike Busch have rolled their eyes a few times over claims of cylinder damage from too rapid leaning. Fits right in with claims of burnt valves from "over-leaning". Funny how no one claims cylinder damage due to rapid advancement of the throttle during takeoff. Time to abandon these myths.

Not only that, but wouldn't ALL the cylinders exhibit the same symptoms if leaning were the cause?

[zav6a]

Take a look at how high the scratches go, either on cam or when you get it apart. You might be able to determine which ring the damage is attributable to. For example, if it only extends up as high as the oil ring travels, that tells you it is probably the oil ring.

If it stops well below the top of the oil ring travel, look for something up with the piston.

[txaviator]

Originally Posted by Noah

Not only that, but wouldn't ALL the cylinders exhibit the same symptoms if leaning were the cause?

I was wondering the exact same thing, Noah. Unless the cooling of this particular cylinder makes it unique. ????????????

[catmandu]

Originally Posted by designerX

For those inquiring about the dental camera here is a link to a newer version of the one purchased (and by the same seller) http://r.ebay.com/7IkF5Q . Note: the head of the camera housing must be cut which is easy and documented somewhere in the Forum.

Counting mine just now, 17 sales in 24 hours, after only one on April 24th. That vendor owes you a commission!

[designerX]

Originally Posted by Noah

Not only that, but wouldn't ALL the cylinders exhibit the same symptoms if leaning were the cause?

Originally Posted by txaviator

I was wondering the exact same thing, Noah. Unless the cooling of this particular cylinder makes it unique. ????????????

I believe Titan Expert was addressing the issue of temperature differential.. not just leaning. Yes the air intake is behind cylinder #3 not at the bottom of the cowl like many RVs. The engine monitor displays very similar CHT for all 4 cylinders but if there were a case of (overly?) aggressive leaning or shock rich/cooling most likely this cylinder would be affected.

[designerX]

Originally Posted by catmandu

Counting mine just now, 17 sales in 24 hours, after only one on April 24th. That vendor owes you a commission!

Hah. The unit pictured looks exactly the same but a 4 mp image will make every minor hone mark that much more frightening.

[Stephen Lindberg]

I, too, have had reservations about shock cooling theory, given that the thermal stresses on a cold engine at start-up must be many times greater than leaning under power. On the other hand, an engine under power is producing much more heat with much more internal pressure. So I don't know what to think, but I move the red levers slowly after giving the engines time to catch their breath after a long climb, for tradition's sake if nothing else. As an aside, the man who taught me to fly told me a hard side slip on a winter's day in an airplane with an OX-5 with short stacks was a sure recipe for warped exhaust valves.

Lovely pictures for a $30 camera. I must have one. Does anyone have a link to the camera modification page?

This hasn't been mentioned yet. The thrust side of the cylinder barrel is 12 o'clock for cylinders 1 and 3 on a four cylinder Lycoming, and 6 o'clock for cylinders 2 and 4. The barrel scoring at 12 o'clock suggests something happening as a consequence of that thrust. I hope the OP posts pictures of the tear down.

[RV10inOz]

I have seen this wear pattern many times over the years, it?s can be caused by rapid expansion of the piston caused by leaning too quickly, rapid cooling of the cylinder by reducing power quickly or a cooling system that is not functioning well.

Old Wives Tale alert. From folk who have done the research on this and measured this stuff (STC work on cooling mods) I am pretty confident in saying that the other causes for scuffing are more likely than leaning quickly. That claim is simply and scientifically not true nor possible.

Parade Rest.

[petehowell]

http://www.csobeech.com/cylinder-camera.html

Lovely pictures for a $30 camera. I must have one. Does anyone have a link to the camera modification page?