New top end break in?

I grew up with being told that you should just run a tank of gas thru it, but not getting on the throttle. The Kawi shop here told me to:run it for 5 min in 3rd gear then let cool all the way down, then run it for 15 min same gear, let it cool down, then 30 mins, let it cool and it's reborn.

Just heat cycle it a few times and your good to go. Don't run the Dog snot out of it but don't just idle and baby it either. Take it through the rev range till it's hot never holding it WFO for more than a split second then let it cool down. Do this 3 times and your good to go. I've put so many top end in old 125 MX bikes and my shifter kart (1 top end every other race) and never had one stick or wear out superfast with the heat cycle method. Also make sure the piston isn't at Top Dead Center when your letting it cool down. Each heat cycle can be done in less than 10 minutes.

oops double post :coocoo:

FTR:

Not everyone is of the same 'heat cycle' opinion.

There is a good argument for NOT being real kind throttle-wise to a new top-end. Yes, make sure the engine is properly warmed up...but full throttle pressures are good for properly seating rings.

I've seen a good number of pics of some pretty old pistons that were broke-in that way. They are pretty clean carbon-wise compared to what you get with the 'cycle' method.

I'm not trying to convince you one way or the other...or voicing someone else's opinion as fact...just saying there is more than one idea out there of what works.

That a heat cycle break-in results in no seizure and long life is nice but longevity isn't altogether the issue.

I sorta use the heat-cycle method in the beginning (first light-up) for the following reasons: you are work hardening and peening things by operation. You are also removing high spots via friction; get it too hot in this scenario and you'll affect the temper a bit because of localized hot spots. Even a little fat on the oil (a LITTLE), a little rich on the mixture (a LITTLE mind you) makes sense for a new motor/ fresh rebuild but isn't required. Holding down the level of friction and localized heat is.

After initial run-in, yeah, you want to cycle conditions which includes varying RPM, varying load, and keeping the motor where it's happy (that means no lugging, with resultant impact to bearing surfaces). It's a progressive thing. After a few cycles ride it like you stole it and finish the seating/peening process. Again, don't overheat.

I know using synthetics with 4-strokes can inhibit ring seating, resulting in very poor performance for a long time, which canyncarvr alludes to. No idea if this is also true of 2-strokes; I would guess not but that is a guess. IMHO, YMMV, etc. etc. etc.