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Re: [turbobike] Compression Ratio

Tue, 9 Nov 1999 09:46:42 -0500

Are you using that Dow Corning Molykote on the skirts?  How is it applied?  When
I worked with them on a development project in a previous life as a piston
engineer, they were promoting a screen printing process.  We found that getting
the coating to stay there over the long haul was difficult, although it has made
its way into some production programs.  Gimmick or true benefit, I'm not really
sure.  Any opinion/data on this?

In my opinion getting the ovality and profile of the skirt right are more
important.  Since the skirt/cylinder interface operates under hydrodynamic
lubrication once the engine is running, frictional loss is a function of the oil
viscosity (shearing forces) as long as there is no hard contact due to a profile
problem.  Therefore the only benefit of the skirt coating should be on startup,
or if the shape of the skirt is marginal to begin with.

I don't mean to bash your process- those are just my thoughts, based on what my
Brazilian friends at Metal Leve taught me.