Depending on the situation we can machine out old valve guides and install new guides.
Some heads have press fit valve guides which we will remove and replace with new if needed.
We carry in stock 450 different sizes of guides and if needed we can machine guides to the size needed.
Also, in some cases we can knurl the old guide to size, but this is a fix that doesn't have as much longevity as replacement.
We see this repair a lot from exhaust studs seized into the cylinder head and broken off at exhaust gasket surface. We use a repair system that removes old stud and repairs the hole with a thin wall threaded insert