ABC Engine Break In, by Mike Fuller

You will not see complete and comprehensive printed directions for breaking in an ABC (aluminum piston, bronze sleeve, chromed) type motor to get the maximum performance from it.

In a proper break in there are two things that must happen in the first two minutes of run time, and the initial heating of the liner (bronze sleeve chrome plated). As much heat must be put into the liner as possible to gain the most one time thermal expansion.  The difficulty is in getting it as hot as possible without the engine being run lean because the connecting rod bushing need plenty of oil.

The best way to accomplish this is to run a very small prop (two inches less in diameter for a .15 or .25) in the 24-25K rpm range with the needle set to a clean 2 -cycle setting with a noticable increase in rpm's when fuel line is pinched.

After starting you should get the needle set very quickly and let it run for about 1 minute maximum then stop it and let it cool completely. After it is has cooled run it again for about 2 minutes and shut it off allowing it to cool completely. Then run a tank full and pinch line very so often to bring it both peak rpm and peak temperature.  After this third run the engine is ready for combat.

OEM's will not risk putting any peak potential break-in in writing for fear that some may interpret heat as lean. I am sure there are many different ways people will break them in but this is method is proven and works well.

Go to www.JETTENGINEERING.COM and read his comments on engine break-in's. This initial heating is so critical that he sells his engines with the initial running already done and guarantees minimum rpm's. If he left it up to the owners results would vary.

November 9th, Engine Break in Test - I used Mike Fuller's break in method on two OS LA .15s today.   These are the Control Line versions, without carburetors, and had the muffler baffles opened before running.  The engine's phillips head screws were replaced with hex head bolts prior to the first run: Conditions: 58 degrees, and 42% humidity.  PowerMaster 15% nitro fuel, 18% oil (1/3rd castor, 2/3rds synthetic), and a special "break in prop".  A Master Airscrew 7X4 was cut down to 5-7/8" and balanced prior to first run.  The engine was equipped with a DuBro 2-1/4" spinner. Run #1 - 30 seconds, engine started and needle valve set immediately for "clean" two cycle.  By clean we mean that the engine was not making any cackling sounds so familiar when running rich.  At the end of thirty seconds the engine was shut off by pinching the fuel line and allowed to cool to the touch. Run #2 - identical to run #1 Run #3 - three minutes.  Needle valve leaned in slightly to keep engine from having rich cackle, as we wanted a clean two cycle setting.  At thirty second intervals the fuel line was pinched for five seconds to peak the engine.  At the of three minutes the rpms on the break in prop were 21,800. Runs 4 & 5 - identical to three. RPMs up slightly to 22,400 at end of run #4. Run 6 - to test performance of engine with MA 7X4 which is the intended flight prop.  19,200rpms peak.