If Rings Don't Seat:

[jhv48]

Here's the deal, I recently had my Roush 427sr rebuilt from heads to pistons to bearings. It was broken in on the chassis dyno with royal purple 20w50 XPR high zinc synthetic oil.

The pistons were replaced using the same weisco pistons and plasma moly rings
that came in the engine originally. Since the rebuild (3000 miles), I have been burning a quart of oil per 250 miles.

There is no smoke on hard acceleration or steady deceleration. The backs of the valves are clean, so it's not valve guides or seals. We ran both a compression and leak down and all cylinders are at less than 5% leak down. Compression is where it should be too. We stuck a bore scope in each of the cylinders and couldn't see anything out of the ordinary. Cylinders were still clean with cross hatch showing.

So my question is this, if the rings didn't seat, then why are the leak down and compression numbers so good? Did the first two rings seat and the oil rings fail?

Is it possible the oil is so thick and slippery that the oil ring can't adequately scrape the heavy oil from the cylinder wall allowing it to remain on the walls and ultimately be burned?

The only other thought is that the block wasn't honed smooth enough for the plasma moly rings (the cross hatch is still visible on the cylinder walls). Plasma moly rings seem to require a finer hone rather than a rougher one.

So, I'm going to change to dino 10w30 oil and try the break in procedures again. If that doesn't work, I don't know what to look at next.

Any thoughts from you engine builders?