Burning Oil conundrum

[Mark F.]

Re: Burning Oil conundrum

This exact problem was the topic on one of those Motor Trend TV restoration shows. This particular show is not real accurate when it comes to Corvettes but they did have a 327 based car, C1 I think, so it would have been a 62, come in with the exact complaint that started this thread. They determine there was a gap between the intake and the heads. The fix was to get another intake manifold. How the first one got “too small” was never discussed. FWIW.

Exactly what Joe Lucia has described before in different strings about intake-to-head mating surfaces.

You'd think engineering would have figured out the slope of the head on the intake side and matched it to the slope of the intake mating surfaces (whether aluminum or cast iron).

Could be the problem that the casting angles were mated correctly; but when they are surface-machined (milled), that step is creating a gap at the bottoms of the intake ports (maybe both the head AND the intake ?)

You only need one of those to be "off" and the problem exists either way.

[Joe L.]

Re: Burning Oil conundrum

Could be the problem that the casting angles were mated correctly; but when they are surface-machined (milled), that step is creating a gap at the bottoms of the intake ports (maybe both the head AND the intake ?)

You only need one of those to be "off" and the problem exists either way.

Mark-------

I believe this is exactly the root of the problem. The angularity mismatch between the intake manifold and cylinder head is caused by machining of the cylinder head deck surface, the block deck surface or the intake manifold mating surface. This does not have to be something that occurs post factory, either. I believe the problem can be present in brand new engines. Once-upon-a-time I mated a brand new GM short block with brand new GM cylinder heads and a brand new intake manifold and still had the problem.

As I mentioned previously, if one removes the intake manifold and finds the heads' intake ports wet with oil, particularly on the lower half of the ports, there is a HIGH probability that the "angularity" problem is what is causing oil consumption issues. Oil seen at this point is NOT the result of bad rings, bad valve seals, or worn valve guides/stems.

There is one other possibility, though: it can be the result of excessive oil passage through the PCV system. However, if this is the case, there will usually be very noticeable oil wetting seen in the intake manifold plenum beneath the carburetor.

[Philip A.]