Hi folks.
I was testing props today on my OS55AX with a Weson Uk minipipe.
After running 11x6, 11x7, and 11x8 i was left with very dark burnt oil residue on the wing.
I've posted a couple of pictures below. The engine runs spot on in all was, but should i be concerned about the black colour of the residue??
Constructive opinions appreciated

That is usually the result of aluminum/aluminum rubbing. Check your header mount with the engine to see if there is some abrasion going on there. Assuming the engine has been run in already? A new engine might produce this as the parts are wearing in, initially.

Originally Posted by RCFVR

That is usually the result of aluminum/aluminum rubbing. Check your header mount with the engine to see if there is some abrasion going on there. Assuming the engine has been run in already? A new engine might produce this as the parts are wearing in, initially.

Thanks for the reply.
If it were "aluminum/aluminum rubbing " wouldn't there be silvery flecks of alloy in the oil
It's not a new engine but in good condion and certainly no-where near worn out.

Aluminium to aluminium rubbing on a small level makes a dark residue when mixed with a liquid, wether oil, water or grease.
Try running some 600/1000 grit wet sandpaper on aluminium with some oil. Youl see it getting a very dark grey coulour.

Are you using a gasket on the pipe header?

The header might be rubbing on the muffler inside the coupling?

Unscrew the header from the engine and check if it is black when it comes out of the engine or if it created at the header to muffler joint.

Some glow fuels do that too. Especially if the engine is leaned out towards the hairy edge of being on the verge of too lean. The oils in the fuel can turn black like that when burned.

When running a tuned pipe some of the burnt fuel is forced back into the cylinder just before the exhaust port closes due to a high pressure pulse. This recirculation of burnt fuel causes it to be burnt even more on the next firing stroke. The result is black exhaust oil, it's just an artifact of using a pipe and nothing to worry about if there's no sparkly bits in it.

Originally Posted by AndyOne

When running a tuned pipe some of the burnt fuel is forced back into the cylinder just before the exhaust port closes due to a high pressure pulse. This recirculation of burnt fuel causes it to be burnt even more on the next firing stroke. The result is black exhaust oil, it's just an artifact of using a pipe and nothing to worry about if there's no sparkly bits in it.

Thanks for the replies folks.
I'm inclined to "run" with the reply from "AndyOne"
Thanks all