Jar,
And all those other people that are snowed in and want to adjust there lifters!!
The first thing to do is to ensure your lifters (rocker arms) are properly adjusted. You have many suggestions in this thread as how to do that if they are stock 1968 4V castings( I also have a pair) with 3/8 diameter studs that are not “posi stop” (my bad on the posi lock reference) of design. Posi stop usually is in reference to a positive lock nut for rocker arms. The easiest way to tell is by the stud diameter. This way you do not need to disassemble the rocker arms. So many things happen during production that always makes me never speak in exact dates or absolutes for running changes in design.
There are many noises that can simulate a “clicking” lifter. Fuel pumps are one area. I have an “auto” stethoscope that I use. There is always the screwdriver to the ear trick. If it is a lifter, even telling it from on bank or another is a challenge. If they are not posi stop in nature, then the best thing to do is a total readjust before you do anything.
We will assume that they are not posi stop in nature and can be adjusted by the nut in the center of the rocker arm. This is how I would do it. First open the hood and locate your top dead center (TDC) mark on the vibration damper used for timing the engine. Mark it with a nice line of white chalk. Then to the best of your ability, and it does not need to be highly accurate, put a mark directly opposite of the TDC on the damper and one half way between the bottom mark and the TDC. Sort of divide the damper up into four 15 minute marks of a clock, or every 90 degrees. Get the engine up to full operating temperature. I recommend a short drive and not just sitting in the garage. Then remove the valve covers. Get a 15/16 inch ½ drive socket and short extension to roll the motor by the vibration damper bolt in the center of the lower pulley. I personally like to remove the distributor cap, spark plug wires, and spark plugs. Makes rolling the motor very easily. Of note , notice which spark plug wire that comes from the most forward spark plug on the passenger side of the engine. This is number 1. Use the ratchet and socket to roll the motor, in a clockwise direction, as you are looking over the radiator. That is the direction the engine runs. Watch the rotor and use the distributor cap to estimate when the rotor is pointing at the number one wire on the cap. As you roll and it gets close to this location on the distributor cap look down at the damper. You will see the top dead center mark come into view and line it up with the pointer. You now have the number one piston at TDC and both its rocker arms completely lose and ready to check adjustment. The above is the only way to ensure that the rocker arms are in the full relaxed position. Do not just roll the engine and watch valves close to determine this. Many a set of lifters is misadjusted that way.
Since we think they are correct in adjustment I would be careful as I un-adjust them to check. Most hydraulic lifters are set between ¼ turn to one turn of the rocker arm nut past a term called zero lash. Before you do anything I would first grasp the end of the number one rocker arms at the valve side and see if you can gently lift them or feel play between the rocker tip and the valve stems. You can also move it side to side on the valve stem (not very much on a rail style rocker) and it should feel like it is tight to the valve stem. So if they feel tight, in a counter clockwise direction loosen both rocker arm nuts ¼ of a turn. Then repeat the above. If they were correctly adjusted somewhere between ¼ and 1 turn you should start to get play between the rocker arm tip and the valve stem. Now that they are loose, you can adjust them. The push rods should rotate very freely if you grasp them and spin them in your fingers. Now start in to discover zero lash for each rocker arm. I like to just nudge the rocker arms say a 1/16 of a turn clockwise in. Then spin the push rod. If it still fells loose you have play. Nudge the rocker arm again and when the pushrod starts to spin much harder, you have it very close to zero. Back off and go in a couple times and get the feel. After a couple times you will find this point of zero lash easily. For stock hydraulic lifters I then slowly turn the rocker arm ½ turn in to load them. ¼ turn for anti-pump up higher performance lifters. This has worked well for me over the years.
Ok, now number one is done! Grab the ratchet and roll the motor 90 degrees to the next chalk mark on the damper. Number 5 is now at top dead center. The spark plugs are 1 to 4 starting at the front of the passenger side and 5 to 8 from front to back on the driver side. So go to the front two rocker arms on the driver’s side and repeat above. The firing order is 15426378. When you are done, you will have rolled the engine two times and the TDC mark will come up if you roll 90 degrees more after you adjust the number 8 rocker arms. The rotor should be pointing at the number one wire on the distributor gap. Do not follow some of those “motors” manuals procedures that talk about adjusting multiple rocker arms at various positions on the crank. It assumes a stock camshaft and the above method is fool proof. There is an engine running procedure with a valve cover with the top cut out. It can be very messy, and if you are not careful you can hurt parts by turning tightening the rocker arm nut to quickly.
Put the valve covers back on and reinstall the cap, wires and spark plugs. Do this before you spend any money.
If you do have posi stop rocker arms, you can roll the engine through the firing order as above and see if any feel lose. If you find one, a longer push rod may fix your clicking.
Rob