Again thanks for your comments. Regarding failure mechanisms in ? air cooled lawn related engines. Is "low oil" the same as "heat kills?" You did mention cowling important in thermal design of the rig (reminds me of VW. My measurements and others' experiences show these engines running 280F oil in summer and I have measured 304 F on the head. This is on its way to 380F where the aluminum starts to creep (soften). The intek pushed an exhaust guide which I theorized was softened aluminum losing grip. Whadda ya think?
I would not think anything untill I saw everything.
Most times guides shift in the head it was due to bad fitting in the first place usually combined with insufficient clearances and possibly overheating to boot.
Valve guides are not under any real stress if the floor is machined nice & square.
Now as for your numbers some where some one has got their units mixed up .
400 deg C is where you should start to worry not 380 F.
This transittion temperature will also vary greatly depending upon the exact alloy being used.
heads are generally Al-Si-Cu-Mg alloys with controlled Fe.
Strictly speaking Fe is an impurity in Al casting alloys as it readily forms Fe-Si which are really hard & brittle.
However scrap Al is cheap & has high Fe content . Fe will form a high strength skin on the surface of the mould so facilitates clean & early stripping so die casters keep it as high as permissible depending upon the actual Si content.
As a home project it is worthwile to do a guide but as a work shop job again not cost effective as the price of a new head is less than the parts & labour to fix the old one.
You will need to rebore , note I said bore not drill , out the old guide hole and get an oversized valve guide you need a .002" to .005" interfearence fit.
This oft requires some lathe work as I have never seen oversized guides.
'The other alternative is to build up the guide hole and bore it out to suit the std guide.
You will see a lot of people recommending some sort of epoxy , Some times you get away with it some times you don't .It is a bit too hot for most epoxies.
You could also try some thing like loctite high temp bearing retainer.
Home owners can get away with these sorts of repairs because if it fails, tough luck but not the same if you are taking some ones hard earned so it is a new head for me.
Inteks have a big design flaw in that the bridge between the pushrod chamber & the cylinder is too thin for the position of the head bolts.
It really needs another one in the middle of this section or a lot more metal.