Hi guys! I've found that yous are probably the best source of information when it comes to giving advice.
Im gonna change a headgasket on my car. With a headgasket kit I got the valve steam seals. Now, my car's done 270 000 km and I thought if I already got those seals maybe I should buy and put the new valves in as well.
A friend of mine said that this wouldn't be a good idea cause new valves probably wouldn't sit properly in the head that's done so many Ks. Furdermore he said even if it increases compression it then wouldn't be good for the worn piston rings and block. He suggested that I would be better of buying another second hand head that did less Ks...
What is your oppinion on this?

tell him to stfu and go back to his magazines

nothing wrong with new valves in a high KM head, i doubt a head would warp enough to cause valve/valve seat misalignments

if the valve seats have worn, it's not that much of an issue getting them replaced, nor is it a problem to get the valve guides replaced

neither of these are attributable to new valves, and any problems that will show up with new valves would be evident before the engine came apart

with the new valves, just get the valve giudes and seatc checked, get the valve seats re-cut and get the valves ground to suit

tell your friend he is f**k but kind of right

new valves in ANY head will not seat right
you will need to lap the valves into the head be it a 2nd hand head with high k's or low k's even a brand new or recoed head will have to have the new valves lapped in.
with the head off might as well go get it recoed with a port matching for a bit more grunt.

if your pistons/rings are in good order there should be no problems with the better compression ( not sure how much ) will be very little mayeb 1-2points at most ( unless your valves are really f**k )

you may want to do a full engine rebuild with a engine with that many kays, the head is off anyways get that done :) then get new pistons/rings bottem end bearings etc and you car will be good for years of motoring