I was putting my motor together this weekend, thinking I would be done fairly soon, but I don't know what happened. I'm using a stock '88 5.0 H.O. short block, comp cam with .512 lift and 220 duration at .050 stock length hardened pushrods, 1.6 roller rockers and edelbrock performer RPM heads with a 1.9 intake valve. I heard that since the cam is not that wild it will slide right in with no problems, but I checked piston to valve clearance without the gasket (thinking that because the gasket is about .04 inches think I could throw that into the equation later) and the valve actually made a bit of contact with the piston. I checked the clearance with clay, and there was none left. The rockers were set right, and it was the intake valve, not the exhaust that hit too. The timing is right, lifters are used so they have oil, but aren't overly pumped, so I don't know what could be wrong. Any ideas?