By Bob Donalds
Just as with the engine in a brand new car, a rebuilt engine needs a break-in period to insure long life and low oil consumption. The new rings, lifters and valves have to find their place in the scheme of things.
The new rings and cylinders generate a lot of friction during the break-in. The bore has a cross-hatch scratched into it, and dragging rings across the freshly honed bore creates initial frictions that are only there until the rings seat. Three rings on four pistons moving up and down real fast, even at low RPM, create a lot of heat in a new motor, and this is extra heat the new motor has to contend with.
Oil is a very good heat exchanger as well as lubricant. I change the motor oil twice in the first thousand miles. Any name-brand 10-30 oil will do the job. The used oil comes out looking like metal flake because it has the residue from the rings and cylinder walls.
You will see a decrease in crankcase pressure when the rings finally seat properly.
I use new or reground OEM (Original Equipment Manufacturer) camshafts and German lifters in my engines. If lubricated properly, these pieces will work-harden. If they become dry, they will scuff and wear out rather than break in. After-market camshafts are not induction-hardened as are the OEM camshafts, and must rely on a hard lifter to harden themselves. I prefer a hardened camshaft to start with. This makes an even playing field for all the parts.
A fresh valve job produces a good seal in the heads and good compression. (Pressure is heat!) Valves will work into the seats very quickly and the clearance needs to be checked twice in the first thousand miles. I am also very big on spring tension. Those valves should follow the camshaft as closely as possible. They should not float. Most valve-train damage occurs from pounding as they float. I use new springs and sometimes shim them for higher pressure.
The rebuilt engine is oil- and air-cooled, and, as you can tell, overheats even before putting a load on it. So how can you take care of this overheating new engine you just spent money on?
Keep it as cool as possible. Make sure you install the whole cooling system and all fresh-air tubing. Set the timing as best you can. Before you actually start the engine MAKE SURE you have oil pressure. Crank it over with the coil wire removed and watch for the oil light to go out. Now attach the coil wire and start the engine.
Above all, let it idle for at least the first twenty minutes. Keep it at 1500 RPM for that time. The reason for this is to keep the cooling fan spinning fast enough to properly cool the oil and heads. Driving it for that first twenty minutes (putting a load on it) would be the worst thing you could do. It creates too much heat and the fan might not spin fast enough. Also, wind resistance on the highway increases with speed and adds to the load put on the engine. This is really true for flat-nosed buses. For this reason, once you do begin driving, keep your speed under 55 mph for the at least the first thousand miles.
One last note about gasoline. If it has been in the car for one year or more, get rid of it. As it enters the exhaust system it is still burning. I have seen exhaust systems glow red-hot because of old fuels.
It has been my experience that small details make or break a project, and these small adjustments and fine tunings are not guess work. After rebuilding an engine, my policy is to review the customer’s installation so that the customer will have the best running engine for the longest possible time. This follow-up is very important, and service not usually offered by other engine rebuilders.