Planing an 880 head with MW domed pistons

To check the clearance install a couple of very light valve springs on one cylinder. Install the head with head gasket of the same thickness you are going to use for final installation. Put the valve train in with push rods and turn the motor over by hand. When each valve reaches it's maximum open postion stop turning and manually push the valve down till it contacts the piston. Use a dial indicator set up on the top of the valve stem to measure how much it moves before it hits the top of the piston. You can do this for each cylinder or use the cylinder with the highest piston deck height (distance from the top of the piston to the top of the cylinder block).

A machinist could probably tell you what the minimum clearance to run for piston/valve clearance. You will want to run a higher spring pressure the closer you get to the piston and the more rpm it runs. To much spring pressure may flatten your cam also.

This is a common misconception but if the valves are going to make contact with the piston, they will do it when the valves are overlapping. This is when both valves are open just a little at the same time. When the valve is all the way open, the piston will be almost half way down in the bore. There is no chance of the valve hitting at that point.

On my diesel pulling tractor, the bottom of the head is flat and I don't run any head gasket so the head is setting right on the block. My pistons come within .040" of the head. My valves open .640" but my valve reliefs machined in the piston are only .250 deep. What I am trying to show you is that if the valves were going to hit the piston when they were all the way open, they would but they never have.

The proper way to check the valve clearance would be to put some clay on top of the piston and put the head on and install the push rods and rockers and set the valve lash on the cylinder you are checking. Then turn the engine over by hand two full turns. Now take off the head and check the thickness of the clay. Most racing engines shoot for atleast .080" clearance. Just remember that if you change your cam timing, these clearances will also change.

This is a common misconception but if the valves are going to make contact with the piston, they will do it when the valves are overlapping. This is when both valves are open just a little at the same time. When the valve is all the way open, the piston will be almost half way down in the bore. There is no chance of the valve hitting at that point.

On my diesel pulling tractor, the bottom of the head is flat and I don't run any head gasket so the head is setting right on the block. My pistons come within .040" of the head. My valves open .640" but my valve reliefs machined in the piston are only .250 deep. What I am trying to show you is that if the valves were going to hit the piston when they were all the way open, they would but they never have.

The proper way to check the valve clearance would be to put some clay on top of the piston and put the head on and then turn the engine over by hand two turns. Now take off the head and check the thickness of the clay. Most racing engines shoot for atleast .080" clearance. Just remember that if you change your cam timing, these clearances will also change.