SBC 400 intermittent lifter tick.

[Edelbrock]

Keep it under 3.5K RPM and it never ticks.
Rev it up to 5K RPM intermittently and it never ticks.
Hold the RPM above 3.5K for 5-10 minute and it taps badly.
Once it starts tapping badly, if you let it idle or drive with low RPM for 5-10 minutes, the tap slowly goes away and then disappears.

TAP TAP TAP. Not an exhaust leak, this is a hard lifter tap.

Lifter being starved? Lifter hanging up? Push rod magically shrinking in length and then lengthening itself after you stop rapidly spanking it?

 

[PrairieDrifter]

Sounds like a weak lifter. Could try running some new engine in a bottle or thicker oil to try and help. What oil are you running now?

Otherwise valve adjustment may help some. If you've never messed with it anyways.

 

[fast 99]

aerated oil or bad lifter? Like most everything else today lifter quality has fallen.

 

[Edelbrock]

I was running 10W40 but after noticing the tick after prolonged high RPM, I switched to 20W50. Problem remains.
Should I try 5W30?
Try an engine flush?
Add a quart of trans fluid to the engine for a few hundred miles and then change the oil?
Pull the valve cover and check the rockers with a feeler gauge?
Should I pull the intake manifold and replace all the lifters and pushrods?

 

[fast 99]

my 2 c

Check valve adjustment first it's possible nut backed off or worn cam/valve train parts to near zero lash.

If engine hasn't been maintained ATF might help but I doubt thinner oil would.

I know folks have had problems with offshore lifters. If you do decide to replace them buy name brand. You will have a better luck. Notice I said luck, after installing hundreds of engines it is just that, luck.

 

[Edelbrock]

my 2 c

Check valve adjustment first it's possible nut backed off or worn cam/valve train parts to near zero lash.

If engine hasn't been maintained ATF might help but I doubt thinner oil would.

I know folks have had problems with offshore lifters. If you do decide to replace them buy name brand. You will have a better luck. Notice I said luck, after installing hundreds of engines it is just that, luck.

Whats the best way to check the adjustment? Motor: 400, unknown cam. Late 70's motor?

 

[fast 99]

Valve adjustment with hydraulic lifters 3/4 to 1 down turn from zero lash.

With each valve closed loosen valve adjustment nut until push rod starts to turn easily with 2 fingers. That should be near zero then an additional 3/4 to 1 turn down. Engine will need to be rotated several times. There is a sequence where it can be done in a couple engine rotations provided a stock cam. May be someone else has that sequence. Should also be a you tube video that demonstrates it.