finally have my 66 chevy to where i think its pretty dependable. been driving it for about a month to work and back approx 200 miles a week. from time to time get this strange ticking sound coming from the engine compartment while driving. will last sometimes 2-3 miles then it sound stops? may not happen for several days then all the sudden there it is again. when i hear it water, oil, etc. is all fine. any thoughts, could it be what i have heard called a spark knock??

If hydraulic valves, one could be sticking occasionally. That is, it is under slight collapse causing valve tick..

if it is a hydraulic lifter sticking, what is the fix? and is it going to cause any damage?

It can be removed and cleaned in a solvent or replaced. If it's a very high mileage engine,replacement may be the best option.

Try running a quart of transmission fluid in the engine a few days before oil change time. Trans fluid has a bunch of detergent in it which might clean out the old dirty oil. As long as you are not racing, the extra oil won't hurt a thing.

Joe

could it be a piston pin?
I've had this happen in the 194/250.
It will rattle when there is no load - neither accel nor decel - on the piston. That is, if you put the pedal down, it will stop doing it, since the piston is being pushed down. If you back off totally, it will stop because vacuum sucks the piston up. Right in between - a very light cruise, almost decelerating - you will get a little rattle - that is the piston&pin rattling on a loose rod. Each time I've seen it, it was just one bad actor.

A lifter won't care about accel vs decel, just rpm, how warm the engine is, etc.

If it is the piston pin ,it will have a double knock.

MBHD

DeuceCoupe,
my route to work includes about 12 miles backroads where i drive approx 40-45 mph, doesnt happen at that speed. then i have about 5 miles of hwy speed approx 55 mph. it is at this speed where the sound begins. once it starts it keeps making the noise even if i pull over and let it idle. however i can turn it off for a minute restart and it will be gone. this is a brand new engine maybe 600 miles on it total.

I had a fuel pump once that tapped on and off,,it was a cheap discount brand when compared to the old stock one the only diff was the stock arm was solid formed metal and the replacement was layers of stamped steel,??, went with electric and the sound went away, I could only hear it standing at the engine bay not in the car,,IDK,, maybe the rod was slapping the arm or lobe or something,,

I'm thinking about this and remembering a plate or something between the block and the pump,and I think it had weird wear marks form the arm hitting it???? and there isn't a rod, when my first engines cam shifted that stamped steel arm tore up the lobes and sent the metal into the pump housing,,,long time ago,,

the noise was a lifter/valve noise. i checked all the lash etc. on valves all was great, went to change the oil and discovered the truck was about 2 1/2 qts low of oil. however the oil stick was showing full. i guess it must not have the correct oil stick in it. thanks for all the help