Break-in

ABC Type Engine Break-In

For Cars, Planes, Heli's and Boats

Few topics develop more controversy than ABC type (ABN, AAC, ABL, etc..) engine break-in, especially in the car crowds. With so many engine instruction manuals giving conflicting information regarding ABC type break-in, it's no wonder many folks are confused.

Lets first discuss why ABC engines are broken in differently than ringed or lapped iron piston/ sleeve engines: ABC type engines all have one thing in common, which is the tapered bore and ring-less piston. With the tapered bore, there is an interference between the piston and sleeve above the exhaust port when it is at room temperature, this is referred to as the "pinch". When the engine comes up to operating temp, the top of the sleeve expands (where the combustion heat is) where there is a near zero clearance between the piston and sleeve. This happens because the brass sleeve (in the case of the AAC engine, the aluminum sleeve) has a higher coefficient of expansion, expanding faster and greater than the high silica aluminum alloy that the piston is made of. It is important to get the engine up to operating temp as soon as possible to relieve the pinch so the stresses exerted from the piston pinching in the sleeve are kept to a minimum. If an engine is run too cool (rich), the sleeve does not expand to design fit (near zero clearance) resulting in an engine that will die when it gets warm because the piston actually wore down to fit the cold tapered bored sleeve. If the engine is run too hot (too lean), the sleeve expands further than the piston, resulting in excess clearance between the piston and sleeve, causing combustion gasses to blow past the piston making the engine fade, sag or die. Not to mention that lean needle settings also starve your engine of oil too.

I am a firm believer in achieving maximum engine longevity. I have every interest in teaching you how to have the longest lasting engine since I make fuel and broken/ worn out engines do not burn fuel!! I do not make or sell engine parts and have no interest in you prematurely wearing out your engine just to sell parts. One critical measure we can all take with a new ABC type engine to break it in properly and tune it properly. The other critical measure is to use a quality fuel containing some castor oil in it with a percentage of nitro that the manufacturer recommends.

Break-in of an ABC-type engine is quick and simple and generally takes less than a quart of fuel on most average .40 to .60 size two strokes, a little less for smaller ones like the car engines and more for larger engines.

1st- Partially disassemble the engine, at least remove the head and backplate to inspect the inside for shavings, flashing or debris. Flush it out good with some old fuel to get any fine metallic dust particles left over from the machining process, out of the engine. You would be surprised at how much metallic dust can be flushed out of a new engine, do the flush in an old white cool-whip container and you will see for yourself!

2nd- Install your engine in the car, plane or engine run stand, fill the tank full of fuel and then set all the needle settings to what the initial settings are in the owners manual. Both the low speed and high speed settings in the manual are a starting point. If the engine has an exceptionally tight pinch, making it hard to turn over, you may want to heat up the cylinder head with a heat gun or other means to relieve enough pinch to get it started.

3rd- Fire it up! Toss it on the ground if its a car and make a couple brief medium throttle passes to bring it up to temp. On a plane, just take it to wide open then adjust so it breaks into a clean two-stroke. In a car, once warmed up, bring the engine up to brief full throttle pass and adjust the high speed needle so that the engine has just begun to break into a clean two-stroke running condition (no longer sputtering or missing). Do not lean it out to maximum rpm's, on either a plane or car!

4th- If in a plane, just let it run wide open for 2 to 3 minutes. If its in a car, run it around on the ground using the full range of throttle with brief amounts of full throttle. Do this on a hard surface rather than grass to minimize a heavy load on the engine, like the planes, run it around 2 to 3 minutes.

5th- After the initial 2 to 3 minute run, shut it down and let it cool completely before doing it again. DO NOT force the engine to cool by pouring alcohol or fuel over it, let it cool naturally.

6th- After its cooled down, fire it up again and do the same thing, Just run it a little harder this time. Make sure the high speed needle setting is still allowing it to break into a good clean 2-stroke run, you may have to lean it slightly. Now you want to start paying attention to the low speed needle and start adjusting for crisp throttle response off idle. Shut it down after 2 to 3 minutes of running it around and let it cool.

7th- Again, after a complete cool down, do it again, running it even harder. Now you need to start leaning into the high speed needle a little bit closer to optimum running and get the low speed needle closer to a good clean crisp response. Shut it down after 2 to 3 minutes of running and let it cool completely. Repeat the 7th step one or two more times.

8th- The engine is as broken is as its going to get by this point. Fill the tank up to about half full then start getting the idle needle and throttle stop set to where it will idle for 15 or so seconds without quitting or loading up when you punch it. Set the high speed needle so it runs cleanly without sagging when wide open. If it gets that way, richen it up. As the engine accumulates more run time the tune will change slightly, thats normal, just be aware of it.

As long as you do not run your ABC Type engine too cold (rich) or too hot (lean) you will have an engine that will perform the way it is designed to and have a nice long healthy life.

There is no need to worry about what the engine temp is since that is dependent on so many variables it is not even worth discussing in a break-in or tuning article. Just do not worry about it, if its running crisp and clean without sagging or fading at full throttle it is not too lean and therefore not too hot. If the transition off idle is crisp and clean it is not too rich or too lean. Either case, the temp is a meaningless break-in and tuning tool.