valves tapping

Have a 350 that was just rebuilt ( 1,000 miles ) on it now. It had a Magnum 292 camshaft and lifters installed. Now a few of the liftres are tapping quite loud. Tried adjusting the lifters but no success. No matter what adjustments I make I still have the tap. Could the lifters have failed already? Puzzled!

If the cam wasn't broken in properly you could have worn lobes and lifters.

Even though "flat tappet" lifters look flat they actually have a very slight spherical shape to the bottom. The lobes are tapered to one side. When the engine runs this causes the lifter to spin which reduced wear. If the cam isn't broken in properly the lifter doesn't rotate and the lobe/lifter bottom wears quickly.
One way to check for proper lifter rotation is to put a paint pen dot on the push rods. Run the engine, lift the intake side of the valve cover and see if the dot is twirling around.

Another possiblity is faulty hydraulic lifters, pushrods hitting guides, or rocker problems. Check for "witness marks" on the rocker stud, spring, retainer, guides, pushrods. You may have to pull the intake and inspect each lifter. If the bottom has wear then the matching lobe is probably hurt also.

Before you rip the engine apart be sure the tapping noise is lifters. I've seen people mis-diagnose everthing from loose torque convertor bolts to detonation as loose lifters.

Thanks for the advice Paul. I'll try to look in other directions to eliminate everything so I don't have to tear down the engine. One thing I forgot to mention is that when the engine is cold there doesn't seem to be any tapping. Once the engine warms up it becomes quite noticable.

That's a clue. Two things change when an engine gets to operating temp.
Some clearances get larger (like bearing clearance) and some get smaller (like piston to bore). Piston slap is often more pronounced when cold.

Oil viscosity becomes thinner and combined with larger clearances oil pressure goes down.

The tick also could be simply a header leak. they sound exactly like a ticking valve.

Use a mechanics stethscope to pin point the area of the engine noise. Also try to determine if the noise is repeating at crank speed or 1/2 crank speed.
This may take looking at a timing light (not directly) while listening to the noise.

Good luck

Ok this one a long shot but if you press in studs see if they are still pressed in.

Use a mechanics stethscope to pin point the area of the engine noise.

If you don't have one of those, I've used a length of rubber fuel line before to listen. Actually works pretty well :)

If you don't have one of those, I've used a length of rubber fuel line before to listen. Actually works pretty well :)


a length of wooden dowel, a long screwdriver, etc works well too...:)

What ever happened with this problem? I need to know if it was cam/lifter related. I'm going to do a best of tech on cam lobe wear.