Sunday, November 21, 2010

Glazed cylinder and high oil consumption

Morning John,
I am finishing an annual on a 1949 Stinson with a Franklin Engine. I was checking your website for photos of a glazed cylinder. I suspect after 50 hours break-in that three of the cylinders did not seat.(excess oil burn, three bottom plugs very oily, oil blowing out of breather.
I plan to do a borescope after the differential press check and then a crank case pressure check.
If they did not break in do you suggest any chemical to pour into the cylinder to break the glaze and try again?

Well maybe not so good morning - about your cylinder...
The only solution is to remove the cylinders and re-establish a proper ring finish. And I emphasis proper ring finish. By proper I mean the ability of the hone shop to measure RMS finish and cross hatch pattern. Otherwise it is a random process with random results.

I don't have any pictures of "glazed" cylinders and I doubt they would look very much different from a normal cylinder. Usually, the term 'glazed" is used rather indiscriminately to describe any cylinder where the oil consumption is above normal after the break-in period. It is usually presumed that the reason for high oil consumption and poor compression is because the rings did not seat, but there can be other reasons such as improper rings or cylinder bore distortion. Failure of a cylinder to form compatible wear surfaces "break-in" is typically caused by an improper surface finish. High viscosity oils and poor temperature control are other reasons why rings do not seat.
There is nothing you can pour into the cylinder to dissolve carbon - but carbon is a symptom and not the problem.

The picture below shows what a hone pattern should look line.
Hone Cross-Hatch Finish Geometry

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