How should I run in my rebuilt KX500 ?

[Hillclimb#42]

Synthetics (designed for autos) in the gearbox has cost me a set of clutches. The teflon coated all the discs and plates and essentialy gave me a slipper clutch. I could put it in gear with no clutch and could feather the throttle to get it rolling. After reading the thread on here about breaking in an engine with no pre-lube and no caution for warm-up cycles, I did kinda learn a good point.
  To sum it up in my words: The thinking was that riding the bike under a load and then  the throttle closed during decelleration with clutch still engaged actually seated the rings the best. The idling process actually could cause some gases to flow past the rings. But under a load and then slowing back down with the clutch still in, actually causes the rings to press against the cylinder walls as the gases try to get behind the rings.
  I now do the heat cycle deal twice. Ride easy for a ten to twenty minute cycle. Then rip it pretty hard for a 10 minute cycle without holding the throttle in any position for an extended period. Then its ready for a daily rippin'. I personally don't think it seats up all the way for hours.

   I always run synthetic pre-mix though.
  Let's not forget that "synthetic" is a very broad term. It isn't some fake oil. It is the same oil with as many technological advancements as possible. It lubes the cylinder to prevent wear and keeps it cool to prevent swelling tolerances. Synthetics have been highly developed to do their job better, or they simply would have never made them.

[KX5MOD]

I run in all the engines i build hard. I let them warm up, & go through the gears easy at first to ensure no binding in the tranny or whatever...then i really tan them.
Very rare does a problem occur, & never because of this method...............i say rae because i build alot of engings, both four, & two stroke.
I built my heavily modded K5 , & ran it in real hard. My bike is piped, shaved head, ported, lectron carb, fancy reeds, etc, etc, etc.
Since the build i have burned well over 100 gallons of C-16, & she still runs like a raped ape ..................& i have this thing wide open for very long periods.
It never ceases to amaze me on how tough it is 
I will mention that i do not burn synthetic on the first tank after rebuild....but use 50-1 synthetic after that.

[dangerous dean]

i would also like to point out that i wouldnt use synthetic gear oil in my tranny after having some friction plates disintergrate inside as well, but it does seem like a bit of a 2-way argument over pre-mix though,personally i would use synthetic pre-mix,many others say not. i wouldnt take the risk. I have been in touch with Silkolene and with Castrol and both dont recommend it, but also on the other hand i had a reply from customer services at Langcourt saying "personally" i wouldnt use it whether it meant personally to the person replying or company wide!!! I do have one more person to contact who is a proffessor in motor vehicle development for Porsche who was building race engines using nicasil plated barrels back in the 80s to see what he has to say....case adjourned

[kaw rider]

The premix story will always be a different depends on who you talk to. Some engine builders have first hand experience on what oils make good power or have good wear in motor and are clean burning.

Would you run the same oil if you had a stock K5 motor verus a 140 Hp K5 motor.

[trouble]

An experienced engine builder told me that if he is building a race car engine, then to always put non synthetic oil in the engine for the break in period.  This will seat the rings 'faster'.  However, in a non race engine, it is not a bad thing to start after rebuild with synthetic.  It just takes longer for the rings to seat which is not necessarily a bad thing.  The synthetic reduces wear on the piston and rings during break in and after some time, the seat will actually be a better one than if you had started with a non synthetic oil.