I just have a small question for anyone who can answer it. I just finished rebuilding my chevy 350 small block and needed to know how long should you break in engine.

Thank you

First, I fill it with Shell Rotella oil. It has the zink in it for initial cam break in.
Find TDC, compression stroke for #1, by physically watching the intake valve on #1 open, then close. The next time the marks line up is the compression stroke.

Set the marks at appr 10-12 degrees BTDC.

Install the distributor, static time it by aligning the reluctor or setting the points to where they just start to open. Simply dropping it in and wiring it for the firing order ain't going to cut it.

The rotor is now pointing at #1, wire the cap, in the correct direction.

Fill the carburetor with fuel through the vent. Only use a carburetor and distributor that are in KNOWN condition, and have been recently tested.

Pump the accl pump several times, or dribble some fuel into the engine with a dish soap bottle filled with fresh gasoline. Just a small amount will do.

Set the fast idle on the carb, or have a second person operate the throttle while observing a tachometer.

Purge the cooling system. Either drill a small hole in the thermostat, or open the stat and put a small piece of a plastic straw (the red thing on the can of carb or brake cleaner, it will flow harmlessly into the cooling system when the stat opens) in the opening.

If you have the means, pressure test the cooling system, and always fill it completely before firing the engine.

Double check belt tension, firing order, hose clamps, fuel line clamps, fuel in the tank, and anything else that would make you have to shut the engine down before you've ran it appr 20 minutes.

Fire the engine and keep it at a fast idle for at least 20 minutes, varying the speed between about 1500 and 2500rpm's.

Do not shut it down unless forced to by excessive noise, no oil pressure, temps go past about 220 degrees, massive oil/water leak, etc.

All of the lifters should quiet down within a minute or two, if they don't, shut it down and go back through the valves, you may have missed one?

After you have ran the engine for appr 20 minutes, let it idle long enough to verify the initial timing setting.

Avoid excessive idling of the engine for the first 3 or 4 times that you run it in.

We always remove the oil filter at this point, cut it open and look for excessive metal of any sort.

If the filter is full of metal, you are in big trouble, pull the engine and find out why?

If the filter is clean, place the engine in service, and pull the filter again at appr 100 miles, or after the first outing if you are drag racing only.

The oil filter ALWAYS tells you what it going on that is really BAD inside your engine.

Same with excessive noise, knocking, ticking, etc.

Catching problems early will save hundreds, and even thousands of dollars.
On the first test drive, I pull a hard second gear to 4500, then let off to seat the rings.

Hope this helps someone.