Newold1 wrote: ↑Tue Jan 09, 2018 4:36 pm
They don't scrape against the rods or crankshaft counter weights, they are ground down to fit about .125" to about .060" off the bottom of the rods and the faces and sides of the crankshaft throws to release oil riding and dripping of those pieces and they work quite well at doing that. Many engine builders and thousands of racers use them in engines at rpms as high as 8500 rpms. Have you never seen or heard of these before! I am surprised by that.
Sometimes I feel that I've heard almost everything by this point in my life...
Why do you need a sheet metal piece to "release oil riding and dripping of those pieces" when those pieces are being spun at 6000 rpm or so with a radius of 3-5"? Seems like they'd achieve the release on their own with the thousands of g's in acceleration, right?
It simply seems to me that the commonly stated purpose for crank scrapers makes no sense in light of laws of physics. They won't scrape anything off crankshaft. It doesn't need to, the crankshaft rotation violently throws off everything on its own.
The most sensible beneficial effect that I've heard a scraper has is that it sometimes prevents the oil that is thrown off on its own from the crankshaft from rebounding back to the crankshaft. I can see that being a potential benefit from that sort of oil deflector. I question the magnitude of that benefit, however, given that the truly high budget drysump systems don't have such deflectors. They just have the minimum volume crankcase, depressed atmosphere, separated bays, and a scavenge port in each bay.
For small displacement inline engines, those sheet metal pieces placed very close to the crankshaft may also do something beneficial for gas pressures around the crankshaft, although I'm not convinced.
For large displacement V8 engines, the piston pumping effects on the gas pressures are much larger than the crankshaft rotation effects, and anything that blocks those piston pumping pulses just costs power. For large displacement V8's, the factory engineers don't incorporate scrapers, keep the windage tray relatively far from the rotating assembly, and put large holes into the windage tray on one side. And I believe those trays cost a little bit of power on a stationary dyno, but make a lot of things better in the actual use when the engine is subjected to external g forces.