I recently rebuilt my 1998 4.3, since it spun 2 rod bearings at only 103k and dealership maintainence....

I got a brand new crank from CCS with bearings and I had the rods machined, shot peened and polished. I cleaned and surfaced the block, rebuilt the oil pump, cleaned and surfaced the heads, installed new valve seals.
I got it assembled and dropped in, its all ready to go.

My question is. What is the general break-in procedure on the 4.3vortec engines with the W vin (light weight pistons and crank)?

By no means am I new to engines or rebuilds. I just have more experience with 2strokes, small engines, dohc 4-6 cyls. Just haven't messed with the internals of a 4.3 in a few years, had to remember tons of things for removal and install
Lol.

 

No mention of new pistons or rings, but I will assume that these are what needs broken in. I also assume that the block was bored, hot tanked, all passages cleaned, and new cam bearings/oil galley plugs installed, and the line bore checked by a machine shop. Also assumed is that final cylinder finish is appropriate for type of rings used.

Be sure to replace the radiator and flush out the oil cooler lines and remote oil filter adapter. Bearing material likes to hide in the oil cooler system.

Prime oiling system well with small block Chevy priming tool and drill before starting. Go a minute or so on TDC, then 1/4 turn and 1 minute, 1/4 turn more and 1 minute, etc until you have gone through 2 full revolutions of the crankshaft. Don't crank with starter to get oil pressure up.

Use 10W30 or 5W30 Purpose-made Automotive Break-In oil (not diesel oil, not additive) first couple of hours run-time and don't let idle much. Vary speed of engine and engine load. Around town is great. Try to keep above 2000 and below 4000 RPM. Best to do a few full throttle to 4000 rpm (easy does it) to help seat rings quickly. SES light will probably come on during this time period with misfire codes, and is normal until Crank Sensor Relearn has been done.

After a couple of hours runtime, drain oil, remove filter and cut it open. Inspect both for metal particles (for oil best to let sit overnight in a glass jar as metal tends to settle and you can see it better as a shiny layer). Probably see some, but shouldn't be excessive. Don't know how else to explain this.

Fill with 5W30 Non-synthetic oil and change oil filter. Do Crankshaft Sensor Relearn. Run 1000 miles doing occasional full throttle to 4000 rpm maybe once per 20-30 miles. Then change oil and filter again to 5W30 non-synthetic for 3000 miles - again with full throttle to 4000 rpm less often than before. After this your engine should be fully broken in and you can put full synthetic in if that is what you want to run (but always use 5W30).

Best wishes!