Mopar engines are inteference type valvetrain. If you put the piston at TDC and press the valve down, you will hit the piston. Cam timing plays a big part in the clearance. Luckily the cam starts to close the valve as the piston approaches TDC. General rule of thumb, if the cam has more than .474 lift and the cam is installed straight up ( 0 degrees), you need to check the clearance.
This is VERY easy, get some modeling clay, make a disk about 3/16 thick of clay, cut it in half, so it is a half circle, place it on the top half of the piston.
Swap a set of light checking springs on the #1 intake and exhaust valves, If you have solid lifters, you dont need to install checking springs.
Spray the valve faces with WD40, set the heads on the block without the gasket, install a set of head bolts for that cylinder, don't torque them, just snug them.
Install the cam and degree it to where you want it. THe measure ments you take are only good for the advance/retard you set the cam at.
If you have solid lifters, set lash to zero. If you have hydraulic, you will need a checking pushrod. You want to set the length at zero lash.
Once its all together, turn the engine over by hand (wrench) 3 times so that the valve makes an impression in the clay.
Now cut the clay vertically with a razor blade through the centerline of the valve. There are two ways you can measure this. 1. use a dial calipre and measure the distance from the impression to the piston face with the back rod end of the caliper. or, 2. remove the clay carefully and measure the thickness at the tinnest point with a caliper. add you head gasket thickness to this number, this will be your clearance.
You should have .120 exhaust clearance and .080 on the intake, this is a minimum. Some people go .100 and .060, but that is really cutting it close. Also, remember, valve float = no clearance!
