How long does it take to break in a rebuilt engine?

The break-in of a rebuilt engine is the process in which a new piston ring and cylinder sleeve glide against each other smoothly without damaging either surface. This is done by ensuring that no dry starts occur, the load on the engine is light during start-up, and limits are set to how much RPM can be gained after start-up. The riskiest time for a car owner happens when the vehicle has been abandoned for some time creating parts rusting from condensation.

Why is “break-in” important?

During the break-in process, your engine undergoes a wear-in—rather than a wear-out—process. During this process, critical parts such as bearing surfaces and piston rings seat (fit) to their appropriate clearance specifications. While some clearances will change throughout the life of your car, they are established during break-in.

Other parts need to be properly mated so that seals and gaskets do not fail due to improper surface finishes or interference fits. High-quality bearings or bushings also require a breaking in or running in the period before achieving optimal performance. This is known as break-in oil, which provides ideal slipperiness for the metal components. Breaking in new engines with an inadequate amount of lubricant could lead to metal-to-metal contact, which would result in engine failure.

How long does it take to break in a rebuilt engine?

This is a common question people have when buying a rebuild. In the old days, before computer-controlled automotive engines, it could take several thousand miles to get an engine broken in and operate at peak efficiency. This was mostly due to valves not getting sufficient clearance from the seats because of carbon buildup or incorrect valve adjustment.

Today’s automotive engines are very different compared to older designs. They operate much cleaner and use special alloys for lower friction and longer life expectancy. The one drawback is that many times break-in can take hundreds of miles harder on today’s cars equipped with variable cam timing (VCT) systems such as GM’s Active Fuel Management (AFM), Ford’s EcoBoost engines, Nissan’s VVEL system, or Honda’s i-VTEC system.

This is especially true when aftermarket camshafts are installed. The OEM timing specifications are very conservative to guarantee optimum performance and long engine life. The problem lies in the fact that VCT systems do not always follow original cam timing profiles, resulting in slightly less than optimum performance, increased fuel consumption, lower horsepower numbers, etc. This is why it’s important to follow a break-in procedure that takes into account all factors of an engine rebuild.

Break-In Procedure

If you have decided to use oil that will make your engine easier to break in and provide a more efficient engine once it is completely broken in.

Use an oil filter. Make sure the crankcase has been filled with clean oil of the proper viscosity. Run the engine at idle for at least 30 minutes while listening for any irregular sounds or clatter from loose parts such as valvetrain components, timing chain tensioners, etc. Allow the engine to cool down completely before running again. 

Next, sample several cylinders using a compression tester. The results will show you if any problems need to be addressed before going on a road test which can put an unnecessary strain on parts not yet fully seated and tightened properly. When all cylinders register within specs during this step, it’s time for a road test.

Make sure the VCT system has been thoroughly tested and is working correctly before heading out on the road. If you do not have access to equipment that will allow you to test camshaft timing accurately, we recommend testing the system before your road test by performing several power brake applications at 70 MPH and verifying there is no noticeable change in vehicle speed. This will determine if the VCT system is functioning properly and keep unnecessary strain off parts meeting for the first time.

Drive The Car – Carefully!

Your new engine should be operated conservatively during the break-in procedure. Consumer knowledge about performance engines typically does not coincide with what manufacturers such as Chevrolet or Ford publish in owner manuals concerning break-in procedures. This can lead to unnecessary expensive engine damage, downtime, and frustration.

“I’ve got a brand new crate motor in my car that I built myself,” one enthusiast said. “It runs great at about 1800 RPMs but it has no bottom end power when I get on the gas after 2500 RPM. Do you have any advice?”

Several inexperienced owners do not understand how important it is to follow proper break-in procedures even with motors designed for competition use. When they start their engine up for the first time, they immediately go out and “open it up.” They come back hours later complaining of noise from bearings or damaged pistons because cam lobes have not yet seated properly or valves did not close at the right time.

“We do our best to communicate to people that they should drive conservatively during break-in,” said one successful engine builder. “I even tell them, ‘You’d better not run your new motor up on a cherry picker because if it falls off your garage wall, good chance it’s gonna come apart.’ But every year I see customers who are not willing to accept this advice. They say something like, ‘My crate motor is brand spanking’ new – what could be wrong with it? Why would you sit here and tell me not to run it?’ So I have no other choice but to deny warranty coverage for their first engine.”

Some V6 engines have two camshafts per cylinder bank. Some V8s also have two camshafts per engine, but many others only go as high as one camshaft per cylinder bank. One common problem is using the wrong size or type of oil filter can press against the timing chain and interfere with proper operation. If you are not sure if your application requires a specific type of oil filter, contact Royal Purple Technical Services before adding any aftermarket components to your vehicle.

Tips during the Break in Process

Many different steps can be taken during the lengthy process of breaking in an engine. For example, one approach is driving at less than sixty miles per hour until completion of the first two hundred miles of driving. This allows time to remove all tight spots from moving parts before reaching high speeds where they might cause problems. By taking these types of precautions, the process of breaking in a new engine can be shortened significantly.

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