They are shim adjusted valves clearance normally stay within tolerance pretty well. There are two special tools but not needed. There are two companies that independent auto repair shops "buy" their information from that offer a very reasonable service to do it yourselvers. You can get a one week subscription or year subscription very cheap. The information is year make and model specific repair procedures, service bulletins, component locations, wiring diagrams ect.... great quality information same as the professionals have,much better than generic workshop manuals from parts stores and much cheaper than the factory manual try Alldata which is very easy to navigate http://bit.ly/AllData_Repair_Manuals_Online or Mitchell on line http://bit.ly/Mitchell1_Online_Repair_Manuals and get an online repair manual subscription. Takes about an hour to measure and replace gaskets, 10 minutes each valve to adjust about $8 per shim to adjust.