What is this material blowing by?

This is a new engine (IO-360 parallel valve, standard compression, vetterman exhaust) put together by Aero Sport Power (65 hours so far). I have noticed some seepage on the number 2 cylinder through 1) the hole where EGT probe is installed and 2) The exhaust joint downstream that exhaust pipe assembly.

The stuff is almost semi-solid / rubbery and it took a little bit of effort to clean it up with a screw driver.

Checked the compression on the engine on that cylinder and its 79/80. Spark plugs looked clean. Oil consumption is pretty stable: one qt every 15-20 hours.

Here are some photos:

This is the EGT probe location with the seepage (cyl 2):



This is the exhaust joint downstream the exhaust pipe (cyl 2):


This is how the seepage manifests on the interior of the cowl:



All this accumulation is over 27 hours of tach time.

Any ideas / suggestions?

If it was a diesel it is called slobber - usually loss of oil control on that cylinder. You might give the builder a call and with only 65 hrs, it is best to get this addressed. It could be anywhere from a bad break-in for this cylinder up to a broken ring, but usually it is glazing that would lead to this with a new engine and few hours.

Just my opinion.

Using a quart every 15-20 hours is a good indicator that you do not have oil contol issues. Leave it alone.

The substance that you are seeing is either burnt/dried oil or carbon residue that was washed out of the cylinder from over priming during engine start. It is very common to see these types of stains after an engine start when the engine is over primed or flooded due to the unburned fuel coming out of the exhaust ports loosening carbon deposits and washing the oil film off of the cylinder bore. Even if you did not over prime the engine it is somewaht normal to periodically have some oil expelled from the exhaust during start due to oil seeping past the rings when the engine is not running. Remember these have horizontal cylinders and run much larger piston to cylinder clearances than a liquid cooled automotive engine.

Remove the EGT probe & debur the hole if you haven't already done so. Pull lower plug and clean it. You can recheck plug at annual for further signs of continued oil control issues.