Engine Oil outta Plug Hole
 

Taildragger with a Lyco O-360-A3A with some 600h since ovhl:
Removing the lower spark plug on cylinder #4 (rear LH) during my 100h inspection, I found the plug full of engine oil and another ca 20 drops came out of the hole after removal...

Compressions are good (74/80 on #4), borescope viewing shows no abnormals, and the oil consumption is quite low with 1qt/50h.

Scraper ring gap on bottom of piston letting oil thru or anything else, any takers?
Thanks.

Ring and wall issues are the most common reason for this. However, any blockage in the rocker box drain hose can also cause this. I would check that first. Shortly after a long engine run, loosen the 6 screws and see if oil pours out.

Larry

Good info
 

Larry......good info there......never heard of this but make perfect sense.
Drain clogs up, oil level under valve cover rises and rides down the valve stem and through the valve guide.
Do you clean the return lines every 1000 hours?
Thanks

No. They shouldn't plug up, but @#$% happens sometimes. Could also be a problem in the rocker box that caused it. Best to check the easy stuff first.

Larry

thanks guys, I will check as described...

Possible ignition problem that is causing that plug to not fire at low power. Do a mag check at idle power or at 1000rpm to see if it's an issue. IMO If the cylinder head and top of the piston were dry on borescope inspection, it is unlikely you have a ring , cylinder wall problem. With a quart in 50 hours oil consumption record, it doesn't sound like there is excess oil getting into that cylinder from any source.
Good Luck,
Mahlon

All good?
 

Now we're are on this topic, I found a little oil in the bottom of the cylinder on one bank for my M1B on it's oil change, 95hr TT. Maybe a 1" wide pool, and a 50 or so little lead balls. I get about 10 hrs per quart. Sound in the normal range? The bores were not perfect but looked good overall. No single cylinder stood out, & all leak down in the -2 psi range.

Edit: 15W50 Aeroshell. No preheats, and 90-100F Oil Temp at TO.