I’m running a 91 non HO engine and wanted to install heads with bigger valves and a cam with much higher lift than stock. To find out where I stood for piston to valve clearance, I bolted the new heads to the block with no head gasket. Installed two solid lifters with new cam and rotated the crank by hand. I found the intakes just kissed the piston and the exhaust just touched the carbon on top of the piston. That was my starting point.
Since I didn’t want to use the new heads for the notching and didn’t relish the thought of placing and removing the old cast iron head 20 – 30 times, I opted to cut the ends off one head. Also, since I wanted to do the notching with the piston at TDC, I needed to mill the combustion chamber for depth and clearance for the increased valve diameter.
 


 
I had some 6” 50 grit sanding discs so I roughed up the faces of some valves, rough cut some circles out of the discs with snips and stuck them on the valves with some 5 minute epoxy. With a drop of oil in the guide, install the valve and attach a hand drill to the protruding valve stem. Spinning the valve with the drill, grind the sanding disc round with a hand held 90 degree grinder. I ground the disc to .060” over the new valve size to allow a little wiggle room.
 

 
I made two stops to be able to set the depth of the notch.
 
 
 
I wanted .120” piston to valve clearance, so I found a 5/16” washer .080” thick, then notched it to slide over the valve stem. With a .040 head gasket, this would give me the clearance I wanted. So the process that I used was rotate the crank until the piston was about ½” below the deck and smear some grease around the cyl. wall. Then continue rotating the crank until the piston is at TDC. I did this to capture the grinding dust and it worked well. Place the head on the block as noted below, again, without a head gasket. Once tightened, slide the valves down until they contact the piston. Put the washer on the stem and slide the stop down, pinching the washer between the valve guide and the stop. Tighten the lock screw on the stop and remove the washer. Using the drill again on the valve stem, spin it up and with light pressure on the drill, allow it to grind into the piston until the stop is against the valve guide. Do both valves, remove head and clean out the grinding dust with a shop vac. Lower the piston and wipe any grease out of the bore with a clean rag. Move to the next piston and repeat. With the 50 grit I could do 3 pistons before the edge of the disc showed enough wear to be a concern. And yes, a couple of the disc came off the valve while grinding, no harm, no foul. I wound up using a total of 8 valves counting the 2 that came off.
For numbers 1,4,5 and 8 pistons, the head would be partially located with the dowel in the block. I used four bolts to hold the head down and tightened them once with the head slid down against the head bolts to do the first notch, then loosened and shoved the head up, retightened and ran the notching tool again.
 

 
You can still see the grease in the second piston before I wiped it down.
Got a couple of thousand miles on the engine now including a few trips down the quarter mile. No problems.