Rebuild Break in?

[Kp]

I just bought a rebuilt BBC long block for my burb.
Do I have to do anything to break it in, like you do with a new engine? I'd like to run syth oil, but I know that you have to break in with dino oil. Does that apply to rebuilds?
If so, how many miles, or hours, before I can switch to synthetic?
Thanks!!

 

[southernspeed]

Flat tappet cams need a break in of typically 30 mins at 2000+rpm which I hate doing but I know people who haven't done it and have wiped out a lobe.
Roller cams are ok though. Rings will take a few hundred miles to bed in properly. Just don't rev it too high or keep sustained high rpm for any period. Try not to lug the motor either, just keep everything moving nicely and gently.
Check your fuelling. Too rich will damage bores and pistons fast from fuel wash. Lean (with in reason) isn't too much of a problem whilst running in under light loads and lower revs.
As for switching to synthetic, personally I'd do another dino oil change at 500 miles and then wait 'till 2000 miles before switching.

 

[Kp]

Thanks!

 

[ntsqd]

There's all sorts of methods/routines that people have for breaking in new engines. As SouthernSpeed noted the big issue is a flat tappet cam. If you have a roller cam the break-in requirement is significantly less.

My old boss at a racing engine shop preferred to gently vary the RPM for 15-20 minutes. The cam lobes are only oiled by that oil which gets tossed off the crank & rods, mostly from the big end of the rods. His thinking is that the oil gets thrown different places at different engine speeds, so by varying the engine speed he was making sure that everything got oil tossed on it. I'd say vary it btwn 1500 & 2000 rpm.

Really all you're concerned with in running the engine off-idle is to make sure that all of the burnishing-in that happens has enough oil flowing over it to wash the particles down into the oil pan.

 

[southernspeed]

Yeah I did mine in 3 ten minute sessions back to back with a little cooling in between. I used, like you say, 1500 to 2000. It's a painful process, I hate the thought of a fresh bore and rings howling away like that!