The Hidden Variable

By Lake Speed Jr. and Keith Jones

I have to admit that over the last 16 years of doing field technical support for engine builders around the world, I’ve seen situations where the outcome didn’t fit the known pieces. Those situations have always bothered me, but over time I’ve come to learn that when the outcome doesn’t fit the known parts and pieces, you are missing a variable (or two).

Piston ring break-in and the oil used for that purpose has been one of those areas with a fair number of puzzling outcomes, at least until the last 12 months. For those that don’t know me, I spent 16 years working for Joe Gibbs Racing and then Driven Racing Oil. During that time I also became a member of the Society of Tribologists & Lubrication Engineers (STLE). Within STLE, I am a Certified Lubrication Specialist and Oil Monitoring Analyst. I also hold certificates in Metalworking Fluids, Gasoline and Diesel fuels, so yes, I am a complete engine and chemistry nerd.

However, in the last 12 months, I joined Total Seal Piston Rings and that is where things got really interesting. As discussed in a previous article, piston ring seal is like soup. It’s a combination of many ingredients that must all work together for the soup to be good.

So what does that have to do with hidden variables? Simply put, cylinder bore surface finish is the hidden variable in “ring seal soup.”

I’m not talking about cross hatch angle. We can see and measure that. What I’m talking about is what we can’t see – surface roughness.

What does surface roughness have to do with ring seal soup?