Can I mill the head on a Honda CRF 450

SOURCE: CRF 450 IS LEAKING OIL TROUGH CARBURETOR

Hi there

You should not have oil leaking from the carby. If you have over filled it with oil, then it may be coming from the crankcase breather and then into the airbox, and appearing to come from the carby. If you have not over filled it, then the bike may have blowby problems with compression gasses passing the rings, and in a similar manner forcing oil out the crankcase breather. Not sure about the hole in the side of the cylinder... do you have a picture? Unless its pouring out, or gets worse, I would not be too worried. If you have over filled the oil, maybe time for an oil change to get the level right.

regards
robotek

SOURCE: CRF 450 Honda leaking oil through carburetor

it sounds like your valve/rocker cover to spark plug tube seal is folded over or something. My reason for saying this is, because the only place for oil to get into the plug tube is a bad seal to the cover or the spark plug isn't tight? and that hole is for expelling liquid so it doesn't cook the plug into the head

SOURCE: Valve Adjustment for 2003 Honda CRF 450 R

This should help.

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SOURCE: my crf 450 is leaking engine oil from the air box

is the breather tube venting in the air box bud

SOURCE: 2005 rmz 450 is leaking oil from the cylinder head

Tighten down the cover. If that does not stop the leak then a new gasket would be in order. I doubt the leak has anything to do with any overheating unless it lowered the transmission oil level quite a bit. The "overheating" may just be the oil on the cylinder naturally burning away.