Engine Break-In

The purpose of the "break-in" procedure is to GRADUALLY wear down the "high spots" on components such as rings, piston skirts, cylinder walls, bearings and races, etc. after a motor is fitted with new items. ALL machined parts are imperfect to a certain degree and therefore have "high" and "low" areas which must be mated to those that they roll or rub against to achieve a good running fit. Problems can arise however in the process because the mere act of "rubbing down" the high spots creates abnormally high friction. Friction creates heat. Heat creates expansion. Expansion reduces running clearances and increases friction. More friction, more heat, more expansion... Pretty soon you can see that you are rubbing off MORE than high spots on each part resulting in premature part wear (LOW spots). This is what happens when a motor is broken in too aggressively. You end up with a motor that, at the very least, has abnormally LARGE running clearances throughout. Thus you now have an unnecessarily shortened remaining life for your "new" motor accompanied by reduced performance. If the motor is really abused during early "new life" running, the tight initial clearances may get closed up completely due to heat and expansion and the rotating or reciprocating parts will SEIZE. So how to control this "running in and mating" of moving parts becomes the question...
First, before you even start the motor for the first time, do a "cranking pressure" compression test with a good quality, screw-into-the-spark-plug-hole type compression gage. Ignition off, fuel off, throttle held WIDE OPEN. Kick, pull-rope or cycle the electric starter until the gage reaches its' highest reading and stays there. Note the reading and record it. Don't expect a real high number because the rings and cylinder are not mated yet, but you should see at least 100 psi, sometimes much higher depending on the planned compression ratio, port timing (or camshaft profile if it's a four stroke), etc.. Generally speaking, with fuel, air, spark at approximately the correct time, 100 psi gage pressure and exhaust, the motor will run.

I prefer to break-in motors on a petroleum based oil and then switch to a synthetic afterwards (if it's to be done at all). There's lots of opinions on this...... for better or worse, that's mine. My feelings are that "too slippery" an oil will slow down the break-in process too much and I've even seen 600X cross hatched cylinders, chrome and Nikasil bores where the rings never seated and we attributed it to synthetic oils during break-in. If it's a two stroke, you can add a bit of extra pre-mix oil to the fuel, set the oil pump at a slightly higher than normal base setting, or both for the first tank of fuel, but I'd use a petroleum based oil.
OK. Start the motor and allow it to run at approximately 1500 rpm or so. Shut the choke off absolutely ASAP! The excess fuel that the choke supplies can wash the oil film off the cylinder walls and overheat the ring faces quickly, especially in a four stroke. ALWAYS shut the choke off ASAP on ANY motor for this same reason. NEVER let a motor run for long periods with the choke on to warm it up. NEVER ride, drive, fly or place under load any motor driven device with the choke on. It is a quick route to early death for the rings.
Check immediately for oil and compression leaks around the various gasket sealing locations. ANY LEAKS should be fixed immediately, especially head, base or exhaust gasket areas. If there are none, hold your hand against the cylinder and GENTLY vary the engine speed in neutral between approximately 1500 and 2500 rpm. DO NOT OVER REV! There is no "load" on the engine and over revving is very tough on crankshaft, bearings, etc.! When the engine is warm enough to be uncomfortable on your hand, shut it off. Again check for any leaks. Now let the motor cool down to COLD. THEN, carefully re-torque the head(s) at this time.
Now you're ready for your first ride/drive/flight/whatever. Start the motor and warm-up gently exactly as before. When the motor is uncomfortably warm on your hand, stab her in gear and gently accelerate through each gear using about 1/3 to 1/2 throttle as a shift point. DO NOT BOG or LUG the motor. DO NOT "cruise" at a steady rpm. Vary the engine speed up and down at all times. DO NOT OVER REV either! When you reach top gear immediately slow down and ride back to your origin doing the same thing. Limit your initial ride time to 5 to 10 minutes maximum, all the while touching the cylinder frequently with your hand to sense drastic overheating. ANY signs of excessive heating or abnormal engine noises require immediate SHUT DOWN and investigation/cure of the culprit. If in doubt, DO NOT ride/drive/fly back to the garage and then shut it off... TOW it back! When you're done with the initial ride, let it cool down to COLD again.
Continue this procedure gradually extending the running time to 10 minutes, then 15 minutes, etc.. You can also gradually get a bit more agressive with throttle application (slightly bigger "handfuls/footfuls" of throttle). Speed up, slow down, constantly varying throttle position and going up and down through the gears. Steady cruising at one engine speed or lugging the motor below its' powerband in a higher gear can cause overheating during break-in... AVOID BOTH! Don't worry so much about too high an rpm as VARYING the rpm. Bursts of throttle allow heating and mild expansion which in turn shaves off those high spots while deceleration allows slight cooling and contraction. Stay away from long hills, carrying a passenger or heavy loads during break-in.
After about an hour total riding/driving/flying time has accumulated, recheck cranking compression. As the rings seat, you will see the readings come up and you will also notice improvements in power delivery. Break-in is essentially complete when the readings peak and no longer get higher as more riding time accumulates. For a two stroke, this is typically one to three hours break-in time.
Even after break-in is done, always warm up the engine thoroughly before riding/driving/flying per the above procedure to avoid cold engine excessive wear or even possible "cold seizure" on liquid cooled motors (most frequently occurs in marine or snowmobile applications).

Nikasil

By Larry Carley (Technical writer with over 2000 articles published)

Cylinder wear is something you want to minimize in an engine, so in some applications, the inside surface of the cylinders are coated with a hard, wear-resistant material such as nickel and silicon carbide. Such coatings go under various names, such as “Nikasil” (Mahle Corp.), “Nicom” (U.S. Chrome Corp. of Wisconsin), “NSC” (Millennium Technologies) and others that all use a proprietary blend of nickel and silicon carbide to plate cylinders.
Nickel is the “glue” that holds and supports the particles of silicon carbide on the cylinder wall surface. Silicon carbide is a very hard abrasive material with a hardness second only to diamond. According to one company who uses the process, the coating has a hardness rating of 600 on the Vickers scale, and a sliding hardness of 58 to 60 Rockwell C. The hardness combined with a tendency to attract and hold oil (“oleophilic”) makes these coatings highly wear resistant. To keep it from wearing the piston rings, though, the size of the silicon carbide particles must be very small, typically around 3 to 4 microns in diameter. The particles make up only about 4 percent of the coating.


After a cylinder has been plated, it must be diamond honed to the desired finish and crosshatch. Many OEM nickel-silicone coated cylinders are typically finished to 30 Ra with a two-step diamond plateau. But many performance engine builders prefer a smoother finish ranging from 4 Ra up to 20 Ra, with additional valley depth (RVK) to hold more oil.

Break-in is similar to any engine. The cylinders can be prelubed with ordinary or synthetic motor oil, or assembly lube. One engine builder said its best to load the engine when it is first started up, otherwise you increase the risk of glazing the cylinders until the rings are fully seated.

As for ring compatibility, most of those we interviewed for this article said conventional chrome faced rings are not recommended. Most recommended low tension rings (cast iron, ductile iron or steel).

A Short History
It all started years ago when engineers were looking for ways to reduce engine weight. Aluminum was the most likely material to substitute for cast iron because of its weight advantage. But aluminum is a much softer metal. And you can’t run an uncoated aluminum piston against an uncoated aluminum cylinder – at least not for every long.

Initially, iron cylinder liners were inserted into lightweight aluminum blocks to provide a reliable bore surface. But iron does not transfer heat as efficiently as aluminum, and iron adds weight. It also expands at a different rate than aluminum. So engineers came up with the idea of switching things around, and using iron-plated aluminum pistons in a bare aluminum bore. To increase the bore’s wear resistance, a high silicon alloy was used. The bores were then honed using a process that wore away the soft aluminum but left the hard silicon particles exposed.

The Chevy Vega engine was the first U.S. production application of this new technology – and it proved to be a disaster. The engines burned oil from day one, and it only got worse as the miles added up. The fix, in most cases, was to bore out the block and install cast iron cylinder liners.

Back in the 1960s, a new type of engine called the “Wankel” rotary engine was going to revolutionize the automotive industry (at least that’s what everybody thought at the time). The Wankel used a triangular rotor that wobbled around inside a figure-eight shaped combustion chamber. The engine was capable of extremely high rpms and could produce a lot of horsepower, but sealing the rotor was an issue. The apex seals at the tips of the rotor tended to wear the surface of the engine housing very quickly.

In 1967, Mahle solved the wear problem with a new nickel silicon carbide coating called “Nikasil.” Better yet, the same coating could also be applied to conventional engine cylinders, cylinder liners and sleeves to reduce wear and improve lubricity. Soon BMW, Porsche, Ferrari and Jaguar were using it on their engines. It also became a common coating for chain saw engines, marine outboard motor engines, snowmobile engines, ATV and motorcycle engines, and eventually even Formula One and NASCAR engines.