recent 3.0 top end rebuild smokes - Runit?
 

I just rebuilt the top end (grind, guides, seals) on my 3.0 along with new studs, oil rings (not compression), and a cam grind, and the sucker smokes. I mean smokes (white/blue). Not at startup from cold, but after a couple minutes.

I ran it for 20 minutes at 3000RPMs per the mechanic, drained the oil and refilled the oil. I've only got about 30 minutes of running after the rebuild so far, so obviously, I'm chicken to drive it.

Question : should I drive it? Do the new oil rings need to seat? Should I run it a few miles and then see what happens? Could I damage anything by driving? How long before the plugs show something? It runs very smooth and lots of power, no sounds. OBviously, I don't fully trust the opinion of the mechanic.

That is a break in process. Most of the rebuilt engines smoke. In your case you used old rings. The rings seat into the cylinder. Once you take apart the cylinder from the pistons, the rings dont seat propperly until they seat beacuse the use and friction. Also the oil that you use for lubricate the pistons and cylinders can make the engine to smoke. Wait a few hundred miles until the parts seat properly and the smoke will gone.

Thanks for the response, nitrometano. Looks like I'll be driving it at night for a while, lest my neighbors think I'm spraying for mosquitos.

I've never heard of anybody, ever, ONLY replacing the oil rings in an engine they are rebuilding!!!

Are your cylinders Alusil or Nikasil? And, did you hone or use a glaze-breaker on the cylinders when you had the engine apart?

Did you run the engine at a steady 3000 rpm during the break-in run, or did you vary the speed every few seconds, say from 1800 rpm to 3000 rpm?

Most newly rebuilt engines quit smoking entirely after the first 30 minutes or so ... if the rings seated prpoerly. This is not the same as the usual puff on startup ... so you should monitor the situation over the next few weeks!

Drive it a while, then report back ...

Nikasil. The car had sit for at least a couple years without running. Speedometer says 48K miles and I believe it based on the interior wear. But is was likely hard miles. There was still significant cross hatching on the cylinder walls, so mechanic recommended just doing the oil rings. Sounded weird to me, too. During breaking, I went from 1600 to 2200 for 20 minutes, but mostly constant at 2000, per mechanic.

Well, I took it out on the road, and about 3 miles down all the smoke cleared right up. Running beautifully and exhaust clean as new. Thanks for suggestions and giving me the guts to "just drive it".