I changed mine after it broke while my wife was driving it and of course most of the valves were bent. I ground some new ones in replaced the head gasket, bought a new belt kit which included new pulleys and water pump. The water pump has to be turned to tighten the belt with a special tool which I made out of a piece of steel channel. Simply line the marks up on the tappet rotors and the one on the end of the crankshaft has mark which is set at 6 o'clock turn the water pump and set the mark on the pulley to sign up. It started right up after I had put everything together except no. 3 cylinder misfires, the compression is 180 pounds, the injectors have been cleaned in a sonic tank and I checked the pulses going to the injectors on an oscilloscope. The injector resistance is 12.5 ohms. I have changed the spark plugs for auto lite copper and that appears to be getting a good spark. I'm puzzled, any ideas anybody. I changed the crankshaft sensor and checked the camshaft sensor all ok.