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Old 01-12-2008, 10:44 AM   #10 (permalink)
Dirt Driver
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Quote:
Originally Posted by nate V View Post
Sounds normal to me.
The pistons are very bad at sealing off the cylinders from the oil cavities.
With every compression and combustion stroke you will be getting some excessive blow by that will result in higher oil pressure. Thats just a fact.
Maybe in the most technical and minute of scientific measurements, but in practicality that is NOT a "fact." On top of that, he said the oil pressure goes down when he gets on the throttle which is when cylinder pressures are highest. That's the opposite of what you describe. Besides, the crankcase ventilation system vents what pressure actually does make it into the crankcase.

Blow-by doesn't affect oil pressure unless you get a bunch of fuel in the oil and thin it out. If the engine isn't running seriously rich, then that's not the case. Being a low-mileage rebuilt engine and ASSuming the rings seated correctly, leak down should be well under 10%.

If the crankcase actually did get pressurized enough to see it on the oil pressure gage, oil would be blowing out of every seal on the lower engine.
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