Suit yorself mate: Start gentle, then variate in rpm. Do not run for a long time period at a fixed rpm.
The metal, friction and physics is pretty much the same as I learned in my class. But you do it your way dude.
You asked and I answered. At least think about it for a moment... unless the saw is crap in your eyes already.
Happy nuw 92cc ! Cheers.
Ok, some of what you have been told is good advice, other bits not so much.
will start with some stuff on 4 strokes, and then head over to the 2t stuff.
yes, warm up engine, go gentle on it at that point, make sure all the timing, tuning, cooling system is working correctly, then get it out on the road, and yes, vary the rpm, and the load, (ie, normal moderate city driving), but as has been mentioned, in order to correctly seat the rings, you need some full throttle / max cyld fill time.
Now when doing this, I would not rev out the engine to max rpm, but instead, preferably on a long hill, get into 2nd or 3rd, 1500 rpm, and then go full load up to say 2500 or 3000 depending on the engine size, then change gears and do that again in 4th and 5th (usual disclaimer about observing relevant speed restrictions etc).
Do that a number of times, say 4-5 runs with full throttle application, but keeping the rpm down, this will give a full cyld fill and sets the rings, which is a very important phase of engine break in, (I have seen several engines that were nursed, just idled, and saw no wide open throttle before their first break in service, and they all had large amounts of blow by on the rings, and glazed bores, and were down on compression and power).
Then return to workshop, with variable speed/ throttle, ie city driving.
Check over everything, reset idle if required, sometimes it would be higher, and then dropped later at its first break in service.
Then let cool, and then run again the next day with a general warm up, one run thru the gears at wide open throttle as already mentioned, and then general city driving back to workshop and the car was ready to be collected.
As the owner drove around with general city driving, they would be given the advice that if they did some highway driving, to not just sit on the speed limit for the day, but to vary their speed, so the engine would not just sit at 2600 for example at light throttle for several hrs, and that a wide open throttle when passing would be ok, just dont go max rpm, but each drive, do one run where you would go up another 500 rpm on each full throttle run.
By the time they were back for the 1500km break in service, if they followed that process, things had bedded in correctly, the engine had had many heat cycles, and seen a good variance of rpm and load ranging from idle to full throttle, and rpm from idle to either 3/4 max rpm if it was the wifes family mover, or if it was a higher performance build, then it had seen rpm limited range. Race engines were broken in over an hr of driving at the track, and would see max rpm's sooner due to the quality of the build, and time constraints, and nature of the race engines. ie good tolerances, lighter internal bits, and good balancing etc.
So now we go over to 2t motors, and in particular air cooled chain saws.
Ring seating is important, thus the offered suggestions of wide open throttle under load, without over revving the motor.
The bearings on the crank, and con rod, both big end and little end (Gudgeon) bearing are different to the sleeve bearing shells of the more typical 4 stroke car engine as they are roller ball types, so running a richer oil to both lubricate, and then allow for the oil to hold and then be passed out the exhaust with any fine bedding in worn off material is a good thing, so yes, vary the rpm, dont just pull the throttle unloaded wide open and let it high rev unloaded, infact even when an engine is run in correctly, that is not good for it anyway.
Letting the saw warm up correctly before loading the engine will help the piston to expand evenly to the cyld and not cause any excess scuffing as happens on every new piston when its first run, scuffing wear marks are different to transfer and damage.
As mentioned, the bearings are very different, both the inner and outer ball race, and the balls are hardened and very different to the soft shells of more typical car engines, so running at higher rpm and load is acceptable for these type of bearings.
Then Load up the engine, ie let it work at full throttle, keep the rpms at normal torque cutting range, just the action of cutting will vary the rpm anyway, so warm it up, cut with it, go thru some fuel, cut what you need to, let it idle to cool off and prevent heat soak, and then turn off, refuel as required, and cut wood.
This will give you the best break in procedure for a new saw, prolonged idling, or low throttle runs, ie half or 3/4 throttle run the risk of a less than optimum fuel delivery for the engine, wide open throttle gives best fuel mixture delivery, ie your not running the risk of a less amount of fuel/ oil mix that may reduce the amount of oil for the parts that are yet to bed in correctly with each other, remember the oil is not only there to protect, and provide a lubricating protective film, but also to collect, and help move away part of the bedding in process wear items/ debrits, which are very small, but are there during the bedding in process, if you get a large piece, then something has failed
.
I hope you have found this to be informative and helpful and not just hey a is right and b is wrong.
