Quote:
Originally Posted by Kevyn
well what I did was a poor mans compression test
the first time I did it was right after i bought it and it sounded like one of the seals was weak I guess.
I did it recently after it had cranked and built up oil preassure with fresh oil and it sounded 100% even. From what I understand rotary engine need oil to build up compression so Im guessing it was just so dry it couldnt get any compression. please correct me if im wrong, Im just here to learn.
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The most honest answer is: Sort of...
The engine itself should be able to maintain pressure without the aid of oil. However oil itself is used to lubricate while also resisting mechanical shear stress along the hard seals. In other words a majority of your compression is going to come from the hard seals themselves and the cranking speed at which they turn (IE good battery voltage, and starter motor). The oil, while lubricating the hard seals, also resists shear from the mechanical compression; meaning that the oil is used to help retain the compression of the chamber while not being the primary means of doing so.
Think of it this way: You could have perfect seals that are self lubricating and microscopically uniform; you wouldn't need oil. However in reality you're going to get deviations in the seals, surface, etc, etc, etc which need to be filled in order to retain the maximum amount of pressure within the chamber. That fluid is the oil. Since different viscosities are present depending on the oil, you get different effects from the mechanical shear. Highly viscous oils will impart higher friction (or resistance to movement; in fact viscosity is the internal resistance to movement of a liquid), however this also means that the pressure is better retained as the shear movement of the surfaces do not cause the oil to separate (per-se). A low viscous oil will reduce friction but by the same token not withstand pressure as well.
The oil you use in an engine will largely dictate the ability of the hard seals to retain the pressure. I hope that was easy to follow.
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