tapping when cold

[cjs67]

I have a 67 chevelle with a 396 that has what sounds like a lifter tapping before warmup. It does this while at idle and speeds up with the rpm increase. After I start driving it around the noise stops. What can I do to alleviate this noise? Any ideas? The engine is rebuilt, and is stock rebuild. No aftermarket headers or big cam.
Thanks[/RIGHT]

[shadowgray396]

The noise could be caused by a malfunctioning valve lifters or an exhaust manifold leak. If the noise lasts for more than a minute and completely disappears or dimishes after the engine is warm the most likely cause is an exhaust manifold leak. If the noise only lasts for a few seconds then most likely cause is a valve lifter malfunction. You should start your diagnosis with a visual inspection of the exhaust system. Inspect the exhaust manifolds for leaking gaskets or cracks. Black soot marks where the manifold mates to the cylinder head are key indicators of an exhaust manifold gasket leak. Inspect for broken exhaust manifold bolts. Inspect the gasket area where the manifold bolts to the exhaust pipe. Small exhaust leaks can often self seal once the metal engine parts are heated and expanded.
If there are no signs of an exhaust leak and the noise dissipates a few seconds after starting the vehicle, you should suspect an oil control or valve lifter malfunction. Hydraulic valve lifters use the engines oil pressure to expand the lifter which provides a zero valve lash clearance. This prevents the valves from tapping. When the engine is shut off a valve and spring in the lifter keep it expanded and retain the oil within the lifter. If the valve or spring allows the oil to drain from the lifter, it will collapse. Upon start up the lifter will take a few moments to “pump up” and expand as the oil pressure builds in the engine. During this time the valves may tap since there is clearance between the rocker arm and lifter.

[cjs67]

Thanks, I will check to see if I have an exhaust leak. Should I use an oil additive such as zddp which has more zinc and phosphate or something like the Valvoline 10w 30 racing oil. I put a conventional Valvoline 10w40 in at last oil change. This is the 1st big block older engine I have owned
Thanks

[Czeto]

You can buy "Muscle Car Oil" with more zinc but you are talking about $10 a quart unless you can buy it locally. I use 10w30 with an additive. Unless you drive mega miles use 10w30 oil and change it at least once a year if low miles.

[Ken Hayes]

I'm with Ray and kinda leaning more towards an exhaust leak.

[cjs67]

Thanks guys. I will check the exhaust system for leaks.

[cjs67]

Cranked the car today, and the tapping noise was not there at all. Could this still be an exhaust leak? I would think if it is an exhaust leak it would do it every time I cold cranked it. Any more thoughts on this?

[Ms Grumpy]

May not always happen with a cold start. Weather conditions, humidity, heat, extreme cold, all may make a difference.

[shadowgray396]

When I had my motor rebuilt, and I'm running a roller cam in mine the engine shop sent home a case of Joe Gibbs Driven HR-2 10W-30 motor oil with High Zinc Formulation to use in the motor.

[cjs67]

I wil try putting some oil additive in to see if it helps, and also change to 10w30 instead of 10w40. I have some additive called zddp that I use with every oil change in my Buick Grand National that I will start using in the Chevelle as well.
thanks