Okay, apparently nobody wants to tackle this one.
There are several schools of thought on a proper break-in. The two most common...............
You can go with the published break-in procedures outlined in almost any Owners manual or do a custom break-in. Your choice.
Ask yourself this. How did the established break-in procedures in an Owners manual come about? Basically they are a compromise
between what Engineering wanted and what Marketing thinks will help sell engines.....bottom line.
If engineering had their way there would be a slow and cautious break-in.
If Marketing had their way there would be zero break-in ("Think of the engines we could sell !")
Now, having had the benefit of looking at engines after both schools of thought there are glaring differences in what happens during these two types of break-in procedures. Will try and give you the short version.......yeah, right!
The new honed cylinder. A cylinder having, in essence, grooves cut into it in a cross-hatch pattern for the purpose of holding lubricant. The lubricant in a two stroke serves two main purposes. It will lubricate the parts that ride against it and it will pull heat away from those parts and transfer it into the water jacket.
If you could take a cross-section of a new honed cylinder and look at it closely, such as in a microscope, you would see what would roughly look like mountains and valleys with the mountain tops being very jagged and sharp. Think of a large wave at the beginning of a break with a curl of water at the top. These jagged tops are going to be cut off and worn in by the passing rings of the pistons during the very first part of break-in.
Where will these tiny shards and fragments of metal go? Good question!
Depends on how you break the engine in! We will get to the aluminum piston in a minute. Bear with me here.
Additional oil is always recommended during break-in on the older two-stroke engines. Why? Several reasons. The additional oil supplies a stronger thicker barrier between new parts wearing against each other while their tolerances are being optimized. The additional oil will also help pull the additional heat out of these parts while they are going through break-in. Those are two recognized benefits of additional oil. A third is that the additional oil will help flush particles of break-in debris out of the engine before it has a chance to imbed itself somewhere and cause accelerated wear.
Here is where the piston comes in. Piston materials are nowhere near as hard as cylinder materials and are therefore subject to being imbedded with debris coming off the cylinder bores during break-in. What's the big deal about that? This material, once imbedded, will stay there in the skirt and accelerate the overall wear of the engine during it's life-cycle. The wear will occur between the cylinder walls and the piston skirt. This wear will eventually cause wider than normal clearance between the piston and the cylinder wall which will affect the "signal" pulses between the reeds and the ports (weaker signal=reduced idle quality) and a lessened ability to transfer heat away from the piston (more chance of a stuck piston, coked rings, burned piston, etc.).
So, how do we optimize the break-in procedure to minimize initial internal damage during break-in?
Thermostats have been discussed here at many different levels. Lets just say they are a good thing to keep in your two-stroke and leave it at that.
At idle the engine will run on the thermostat. The block will be at its warmest and therefore the cylinders will be expanded to their widest tolerances.
Pistons however will be on a rich idle circuit, not putting up with much load or heat stress. They will be at their minimum designed in tolerances. Bigger cylinder/smaller piston!
Clearance between pistons and cylinder walls will therefore be at maximum. Max clearances? Great way to flow and flush debris from break-in out of a cylinder!
I have looked at pistons from a low and slow initial break-in and pistons from an accelerated break-in schedule. By far the pistons from the accelerated break-in schedule look like they have been through a war compared with low and slow. Yes, I have looked at these through a microscope.
The pistons that endured the hard break-in will have massive amounts of cast iron debris from the cylinder honing imbedded in them vs. the low and slow initial break-in schedule. Engines that go through the hard break-in process and are run on side by side duty cycles with a low and slow will also see a reduced service life.
By contrast pistons that had a low and slow initial break-in exhibited a minimum amount of debris stuck in the skirts.
So, how do I break-in an engine? Double oil is a must first and foremost.
I will run the first one hour on a hose or in a test tank. At idle only, never past where the thermostat range is exceeded. This gives the engine a good chance to flush itself of break-in debris, etc. during that first critical part of break-in. The first hour is golden to a good break-in.
From that I will go up in RPM for a short burst and back down to an idle. When you go up in RPM you will go up to the point where the thermostat is by-passed and the cylinders cool down and "shrink" to a lesser tolerance. The pistons however will become hotter with the higher duty/load cycle and expand. Bigger piston/smaller cylinder.......rings pushed harder against the cylinder walls again. There goes more debris. That's why I say a short time. That RPM varies but figure around 1500-2000RPM.
Drop the engine back down to idle and flush that debris. Then cycle the engine again for subsequently longer periods. Once you are up on plane don't stay there long. Never run your engine at WOT during the first couple hours if at all possible. No need to. Go trolling or slow sight-seeing.......
Take your time during the initial couple hours of break-in and you will be rewarded with an engine that will give you a long service life.
For those of you that are "lucky" enough to see used pistons on a regular basis....start looking closely at the piston skirts. Look on the thrust side 90 degrees to the pin bore. You may be amazed at what you find.
Sorry for the long winded answer. Now....it should just be a minute before someone comes along and tells you to just follow the manufacturers recommended procedure! Welcome to the marketing side!
