Inadequate Rebuild is More Than a Seating Issue

Dear Car Talk:

I recently had my old, 327 Chevrolet engine completely rebuilt. The motor has around 700 miles on it since the rebuild and is burning almost a quart of oil every 150 miles.

My mechanic says not to worry and that the rings just need to seat. I would like to hear your thoughts. Should I be concerned? -- Edward

Yes. But not as concerned as your mechanic should be.

If you were burning a quart of oil every 750 miles, I might be inclined to believe that the rings still might seat correctly. But you're burning oil at five times that rate, Edward.

So your rings are going to have to do more than seat. They're going to sit on a golden throne.

By the way, "seating" means that the piston rings that go up and down inside the cylinders "conform" to the exact shape of their cylinder walls. When rings are properly seated and perfectly matched up with their cylinder walls, very little oil gets by them and burns up.

Conversely, rings that don't seat properly, or are worn out, let lots of oil past them and result in you burning lots of oil and getting calls from local officials who want to use your vehicle for mosquito control.

Unfortunately, I fear that your rebuild was done inadequately. Your mechanic is, understandably, doing everything he can to avoid having to redo it. It's time-consuming and expensive. But I think that's where you're heading.

You might as well humor him for now, Edward. Tell him you'll drive it for another 500 miles and see what happens. But if the oil burning doesn't drop precipitously by then, he's going to have to go back in and try again.

When you rebuild an engine, you usually have two choices. You can either just hone (rough up) the insides of the cylinder walls and replace the rings. Or you can bore out (increase the size of) the cylinders and then put in new, oversized pistons with new rings. That's probably what he should have done, even though it costs more.

Whatever went wrong, burning a quart of oil every 150 miles after a rebuild is totally unacceptable. If I had an engine rebuilt, and it burned more than a quart every 1,000 miles, I'd be ticked.

So, tell him you'll drive the car a little longer and see if the rings seat. But during that time, set up a webcam outside his shop. And if you see moving trucks pull up, rush over there and get your money back before he relocates to Saskatchewan.

Todays Car-o-Scope

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