A valve job (servicing the valve seats and guides) is complicated and needs special tools, which is why the work should be left to a professional since the valves cannot be serviced. A home mechanic would be able to take the head out to dismantle and perform preliminary cleaning and inspections after which he or she would send it to an automotive machine shop where the actual work is carried out. Using this inspection, it is possible to check the state of the head and the valve train parts, and understand which work and new parts are required in case of cooperation with the shop. It is worth mentioning that the most popular cylinder heads of the Volkswagen have the maximum dimension of the valve seat refacing, which shows the maximum amount of material that can be machined off the valve seats before it is required to replace it, and the shop will measure this index. The shop will also take out the valves and springs, recondition the seats and guides, exam and substitute valves, valve springs, spring retainers and keepers when necessary, recondition valve seals, assemble the parts and check the valve stem height. In case of a cylinder head with warped surface the surface gasket of the cylinder head will be resurfaced provided that this head is at least of the required minimum height. The head will be in like-new condition after the professional job on the valve, and it is necessary to clean it with more cleaning again before reattached to the engine, blowing it out with compressed air where it can be used, to remove all oil holes and passages.