Breaking in rebuilded engine

[Ivan141]

I recognise the Mototune USA retorics, I'll admit I picked up some usefull info on engine's there too. Nevertheless I would not try the 'hard' break-in method he's advising untill I have seen it work for someone else first.
That's why I already said I dont intend to go into this matter, because it's mostly a clash of opinions...I'd rather see some facts.

The things everyone agrees upon: Use mineral oil during break-in, and change it VERY often (especially right after the first couple of km's) because the metal that comes loose will end up in the oil, you need to get it out regularly. Also change the oilfilter. Furthermore the basic stuff to keep a 4age in good order: always warm it up properly.

[BenR]

That is the correct way to bed an engine in.

When you build an engine you set all the tolerances to specific oil clearances, there is no point doing this if your predicting metal on metal contact between any surfaces, as such, bedding in does not need to be done.

The only thing you have to worry about is ring seal efficiency, and Fii and Ivan are 100% right in saying you need to induce high throttle angles to generate cylinder pressures high enough to increase ring tension on the cylinder walls. If you do not, within minutes its pointless.

Do not run in with synthetic, run off synthetic for at least 1000 miles, but change at 100 miles for new mineral oil with NO additives in it.

Use 80% of the rpm range and 100% of the throttle range within the first few miles of warming up, it only takes a few WOT runs to bed the rings from brand new if you use 100% throttle.

Dont be scared, if it was build properly there is no problem

On our dyno we start them (they are pre-heated), get them upto oil pressure, check at 3000rpm, then increase load to 100%, lower it and run it in for 1 hour........then that is done.