Nice attention to detial in that build - love the silver coated engine parts. I did the exhaust valves of another BMW head in a pillar drill. Some strips of emery cloth in various grades and you can polish them as new. I taped where the valve stem enters the valve guide so as not to go above this ( although you can see this because of the carbon build-up ) and also protected the valve seat area,even though they would be re-cut later.
I've no idea if this is a pretty hack way of doing this ,but it worked for me. I would say though if you are not recutting the valves,maybe steer clear or be VERY carefull as its easy to slip and mark the seat area.
Another helpful hint is using Gunk brand brake cleaner (non chlorinated)for the exhaust ports. On my alloy head it stripped the carbon off with no effort at all - great stuff.
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