Dave, here's one you might not have come across before...

I decided to pull my 110 apart to give it its yearly inspection and overhaul. I removed the cylinder from the crankcase and noticed a lot of carbon build-up on the valves, particularly the exhaust one. I removed the valves for de-coking (easy) and also attempted to clean the combustion chamber roof and exhaust port (hard). Having removed the valves I noticed the valve guides and ports have a brass-colored surface leading me to assume that they were brass inserts on the aluminium head, just like OS and Saito do.

Here's the weird part. I placed the cylinder head in a warm water/dishwashing liquid solution overnight to soften up the deposits for easier removal. Next day, I removed the cylinder/head, rinsed it, and noticed that the brass-colored surface of the valve guides had gone (now it looks like natural aluminium)!

Question: Does YS do some special brass-coating process on the valve guides/ports? If yes, is it safe to run the engine now that this coat is seemingly not there? If not, is there any way to re-instate this coating (some specialist sporay, electrolysis,..)?

Many thanks.