If you ask 75 people what the best way to break in a new engine, you will most likely get 75 different answers. One of the best ways to break in an engine is the method recommended by Axtell for their big inch engine kits. This is a technique called heat cycling. This takes a few hours, but eliminates the initial speeding up and slowing down during the first hundred miles or so. Here is an exerpt from Axtells installation instructions listing the procedure for this process.
As a result of increasing your horsepower, whether it is bore, stroke, or a gain in airflow, you must supply the motor with more fuel. Too lean of a fuel mixture is dangerous because it burns more slowly, and requires more time to conduct the heat from the combustion. These are air-cooled engines and they are not nearly as forgiving as water-cooled automobile engines.
If ever in doubt about proper jetting, always enrich in large increments. If the engine is running on a lean mixture, the temperature in your combustion chamber will rise, causing detonation (knock) or pre-ignition, which is an uncontrolled burning of fuel. Pay special attention to low speed jets, as they will control fuel mixture at idle. Changing the main jets will help at highway speed, but will not help control mixture fuel during target break-in rpm range.
Timing is another important factor in heat buildup. Too advanced of a spark will also cause heat build-up. A safe starting point is 32° full advanced.
The first few moments of a motor’s life are the most crucial. Take care to make the aforementioned changes before breaking motor in. Also, make sure to verify that there is proper oil pressure on startup. For these Shovel kits, you need to have at least 20 psi pressure at normal operating temperature at 3000 rpm.
Breaking in your motor is vital to the life of your engine. Axtell’s recommended method of break-in is to heat cycle the motor. Start the motor (with plenty of air blowing over the motor to dissipate heat) and allow it to run for thirty seconds. Allow the motor to completely cool to room temperature. Once cooled, start the motor again and allow it to run for sixty seconds followed by a complete cool down. Repeat this process, adding thirty seconds each time until you have reached four minutes.
Now the vital break-in is done. However, over the course of the next thousand miles, the internal components are still familiarizing themselves with one another, so take special care during that time. Keep your engine under 3500 RPM’s for the first 300 miles, and less than 4000 RPM’s for the first 1000 miles. Do not put a large load on the engine and be careful not to “lug” the engine during the 1000-mile break in period.
Axtell Sales is a high performance engine products provider for Harley Davidson engines. They are the home of the "Mountain Motor," and have some very high quality american made products. If you are looking for a high quality, big inch engine, go to axtellsales.com.