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New Engine Break-in Procedure

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Oct 10, 2011

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Breaking in your new engine
There is plenty of information floating around the Internet about engine break-in, though much of it contradictory and hard-to-find. Being new to engine building, I was particularly uneducated about breaking engines in. Many of the traditional schools of thought preach being gentle and easy on new engines. However, these have been proven wrong. In the old days, when tolerances were very low and metals not what they are today, I can understand why easing an engine into use was a good practice. Things have changed. The honing pattern of the cylinders in modern engines are much tighter than they were in the 1960s and breaking in an engine gently just isn’t beneficial anymore. It does not hit the right friction marks to properly mate the piston rings to the cylinder walls. Several articles I’ve read agree that going light on the throttle does not seat the rings properly against the walls of the cylinders. This means people haven’t been doing what is best for their engines for years. I always assumed it was best to go easy on an engine until it was broken in; but research and dynamometer-proven results have changed my mind.
I have found it difficult to find good information on the proper break-in procedure in one place. I’ve compiled this article to provide a solid set of instructions and information in one place that will answer the majority of questions related to a successful engine break-in.
Most manufacturers persuade you to baby an engine for the first 500 miles and mention nothing about changing the oil early on.
So, after research (sources listed at the end) and speaking with some professionals at machine and motorcycle shops, I’ve assemble my interpretation of new age break-in methods. It’s important to have a systematic approach to something as significant as getting the most out of your engine.

The Procedure
This procedure consists of six phases. Ideally, you want to perform the break-in using a dynamometer (dyno), a device used to measure force. But few people have a dyno handy where they drop their engine in.
The engine’s first 20 miles are the most crucial for seating the piston rings. If this process is not performed early, the roughness of the surfaces will dissipate before proper ring sealing is achieved.
This process applies to all four stroke engines.

(Very Important Factors)
• Under no circumstances should you use synthetic oils for the break-in.
• Do not lug the engine (too much a throttle in too high a gear w/ RPM’s Low).
• Idle the engine as little as possible.
• Do not allow the engine to overheat.
• The idea is to open the throttle and load the engine in the lower gears.
• Avoid torque converter (TC) lock-up and higher gears.
• Ideally (e.g. a four speed tranny) you should use 2nd and 3rd gear when performing the break-in.
• It’s crucial to allow the engine to decelerate on its own. This will create higher vacuum levels.
• Heat cycling the engine between stages is not necessary.
• Remember, it’s not about speed it’s about RPMs and putting a load on the engine.
• Make sure to allow the engine to brake/reduce the speed of the vehicle.
• Phases 2-4 must occur during the first 20 miles.
If you are using a dyno, you should allow a 15 minute cool down between each phase. Do not use the dyno brake to slow the engine during the deceleration after each run. Since most of you will be driving on the street, you will not have to worry about adequate airflow, which a dyno fan may not provide.

Prior to starting the engine for the first time:
• Thoroughly prime the oil system.
• Prime the fuel system.
• Check for leaks in each system.
• Check fluid levels.
• Double check your plug wires.

Phase #1 – Warm up
• Light acceleration and relatively lower RPMs are what you are looking for here.
o No Lugging.
o Idling should be avoided.
• Warm up the engine and check for any leaks. Watch for any issues.
• Attain operating temperature usually between 170 and 210 (this is very important for the following steps).

Phase #2 – First Pull
• Three runs at ½ throttle
• 40-60% of engine’s full RPM range – Holding the gear and allowing the engine to cause decal.

Phase #3 – Second Pull
• Three Runs at ¾ throttle
• 40-80% of engine’s full RPM range – Holding the gear and allowing the engine to cause decal.

Phase #4 – Third Pull
• Three runs at full throttle
• 30-100% of engine’s full RPM range – Holding the gear and allowing the engine to cause decal.

Phase #5 – Finishing the 20
Continue driving, accelerating in short bursts followed by deceleration. Remember not to be light on the throttle, don’t baby the engine. The idea here is to put pressure on the piston rings. After 20 miles, it’s time for your first oil change. Still no synthetics should be used.
At this point, the piston rings are 80% fully mated to the walls.

Phase #6 - Completing
When driving, you should vary the RPM of the engine speed, occasionally loading the engine and decelerating as desired. After about 1,500 miles you're ready to put in whatever engine oil you prefer. At this point your break-in is complete!


The core philosophy of this approach is that you are working the engine up to higher RPMs and seating the rings properly by causing the intake vacuum to change drastically and varying cylinder pressures. If you going to see problems out of an engine taking it easy on it now will just prolong its inevitable failure. I used this procedure after consulting the research and opinions of professionals.


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