Engine rebuild break in
 

I rebuilt my 1.8, fully forged bottom end with new bearings and etc.

Currently I'm in the break in stage and stressing out alittle. I have about over 100 miles on the engine and changed the oil twice. The first change the oil was completely black, the second one it was dark but not as dark. I'm assuming it was the assembly lube making the oil really dark.

As for metal, there wasn't any huge flakes or anything. Just a few tiny specs. Same goes for the filter.

Engine so far doesn't make any knocking sounds, just curious on how many miles should be put on the engine before I'm considered in the clear. Also so I don't have to worry about a bearing failing anymore. Planning on putting 50 more miles on after work...

You will read a lot of conflicting information but here is what i have always done and its worked great.

Run car for 15 minutes on initial start, check for leaks and drain oil. ( use dino oil I used dino rotella )
Run that oil for 50 miles and change it again, more dino oil make sure you are doing a lot of engine braking letting rpms slow the car down and vary rpm a lot, if you are boosted get into light boost but not a lot.
Run the next oil until 250 miles and do more of the same but more boost applied.
@500 miles do another oil change again with dino oil and at this point you can start feeding in more boost.
@1000 miles switch to the oil of your choice and hammer.

Dont be too easy on the engine or the rings wont seat but youre already past that point now.

Yeah I read a lot of ways to break it in, and pretty much what you said is how I'm currently breaking it in. Just stressing out about the bearings potentially failing and etc. Not really worried about the rings.

I used standard sized bearings, crank was polished and etc so it shouldn't have an issue, but its still nerve racking.

If you've made it 100 miles the bearings are fine. The rings seating is always my biggest concern personally.

Drive it how you normally would. Don't go crazy, don't baby it. Mine was getting 20lbs from day one too. Gotta break it in how it's going to be used. :)

You're 100 miles in, i personally believe that a solid highway trip where you burn a full tank of the gas is the best way to seat the valves and really wear in the rings good. Bearings don't care, they either have oil or they don't. There isn't much wear in being done on bearings.

My built BP is heading towards 10 years old now and it never got and never will get any special attention. Doesn't burn oil or do anything funny. Compression is good.

This settled my nerves a little. Will probably drive it accouple more times to work and continue to vary the rpm and vacuum. Then off to tuning!

This build was done by myself with very little to no experience doing this type of stuff. A lot of research and long nights. Hope everything works out. thanks!

I broke my built motor in just like Andy (and many others) suggested. Basically start the car, warm it up, change the oil. Fire it back up, go for a drive, lots of vacuum and a little bit of part throttle boost. Always vary RPMs, part throttle to 5k just to let it see some rpms. I did this for ~35 miles and changed the oil again (probably overkill, but I was using cheap oil). At 50 miles I basically started driving it normal, but kept it out of redline and high boost. Around 100 miles I basically started tipping into low boost, and by 250 miles I was running 8-10psi.

I waited to go to a full synthetic until 1,000 miles, then went with rotella t6. My bp and b6 mazda engines always loved the stuff.

I just turned over 10k on my engine built recently. It runs super strong and doesn't use much oil (I don't have to add any between oil changes at ~3k interval).

Super happy with it. Hope yours goes well too.

Rebuilt my own with rods, hone and rings. Used oem pistons from another engine and only measured bearing races.
i drove it with 7 psi the first few times, approx 10 miles and then raised boost to 15~ and just ran it.

The only thing I fuckrd were the crank case, i never sealed the chambers and that pushed some clear oil out of my welded -10 AN fittings.
With that sealed i get close to zero oil in my catch cans.
My piston rings were gapped originally to first 0,45mm and second to 0,5mm, definitely larger than OEM but no way I will make them kiss each other.

Have run this setup with a GT2560R and still 15psi for about 1k miles and I assume this will hold up great for the coming years.

I am almost in the same position as you right now. Little over 100miles on my new forged engine. The first oil change after first warm up and run looked real dark. I also thought it must have been assembly lube and additional wear from initial ring breakin. I have a magnetic drain plug and it had no shavings or anything on it. Changed the next batch of oil at 50miles. It was still darker, but nothing like the first oil change.
I just checked the oil this past week and the dipstick oil looked clear and fresh. I am planning another oil change at 250miles, Dino oil is cheap!

I need to cut open my first two oil filers and see what they look like.