Just to add to the mix...
I've always heard that when you first start the motor, you should run it a about 2000rpm for about 15-20min to break in the cam. Set the timing as best you can, fill the carbs with gas THEN start the motor and don't shut it down for minor leaks or problems untill the 15-20mins are up.
It worked for me. Twice (thats all the experience i have)

There are two different problems here.

The most common types of rings commonly used for rebuilds are chrome barrel faced and cast iron plain face. Both require different run in techniques.
Cast rings seat very quickly and can be "given death" after a very short time if correct ring gaps are used.

If you are using chrome barrel faced rings these have a smaller face area in contact with the bore but are harder to bed in. Giving these "death" after a short while will cause the ring to burn on the face, seize, loose tension or break.

Oil has a big part is break in as mentioned. Lighter oils allow more face contact before shear occurs meaning break in of the face occurs earlier.

Ring end gap is very important as well. In a performance engine where minimising blow by (wasted horsepower, dirtier oil) tighter ring gaps are used and a slower break in used to prevent thermal stress on the ring until fully seated in the bore.

I agree about running at same revs and lightly loaded for too long.

"Total Seal" manufacturers of Gapless race rings recommend the break in process should be :-

"Do not allow the engine to idle for long periods, mildy load the engine as soon as you can. Highway driving is a good way to seat the rings quickly. Do not use synthetc oils during break in. After 2000 - 3000 miles the rings should be sufficiently seated so regular oil can be used"

i am confused i dont know what i am gunna do with my new engine now everybody has different views

i am confused i dont know what i am gunna do with my new engine now everybody has different views

My old mans a mechanic and he always told me the worst thing you can do to a newly built engine is to run at the same revs and lightly loaded for too long. Alternate your revs and use the gearbox to help seat the rings. I'm with the other guys on the mineral oil too you can't run in an engine with synthetics. We normally fire an engine and run it at fast idle for 1/2 an hour, check for leaks and then take it for a good 3 hr drive on the open road. There is nothing like slipping a full race engine in a Sunny shopping cart and going for a good hoon... And Feral I'm not saying your Sunny is a shopping cart either !!!

ahh good someone does agree with me (from other post where i said similiar)

ive never realy run in my engines. i just start them take them for a 5 minute drive under 4thou and then retouque the head etc and then give them death. then change the oil after 1000 k or so. its only the euro motors that need heeps of runing in because theyre made to do 1/4 million miles. My girlfriends father races a mk1 vw golf gti and hes been told his new 1800 motor wont be fully run in for 5-7000km! its ok to give it heeps but it wont reach its full proformance till then. Any way ive never had any problems and i know a few pros who do the same.

I am using a good mineral oil. Castrol GTX2. I am planning on running it with that for another 1000 or so and then use Mobil 1. I have not seen it smoking at all, reckon it will be alright.
cheers

check your PM pirre

go to your speed shop and get some running in oil we here in new zealand use this alot when we build our race engines
try not to leave the motor running at idle for to long as this can cause the bores to glaze up good luck