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MG MGA - Crank Scraper
|Anyone have any thoughts about these? Just curious if they are effective.|
|I have always regarded the selllers of "crank scrapers" in the same category as sellers of "snake oil".|
How can it scrape oil off the crankshaft, it does not touch the crankshaft? Any oil on the crankshaft is thrown off immediately by the very high centrifugal force. The only thing that it might do is reduce the oil thrown onto the cylinder walls and help increase wear. I like oil being thrown onto the camshaft lobes, oil pump spindle drive gears etc....etc......
|Pistons, con-rods and crankshaft turn up a veritable tornado of air turbulence in the crankcase at very high engine speed. The "crank scraper" is intended to shield oil in the sump from some of this turbulence to prevent frothing and foaming in the oil (as air bubbles make for poor lubrication of crankshaft bearings). This might do some good on a race engine the runs for extended periods of time in excess of red line speed (6000+ rpm).|
For a street engine, forget the crank scraper, totally unnecessary and probably no benefit at all. I run the crap out of my MGA, sometimes at the yellow line (5500 rpm) for hours on end, and fairly often far beyond the red line (6000-7500 rpm) briefly while auto crossing. I have never had any lubrication problems related to air entrainment in the oil (but have previously melted rod bearings after cavitation of the oil pump).
|The "windage trays" that I have seen do not have the conrods passing through them. They consist of a tray fitted just above the oil surface in the oil pan, with cutouts only at the sides to allow oil to drain back into the pan.|
If you use a race engine at very high RPM which could cause aeration at the surface of the oil in the pan, or have oil starvation at the pump due to high "G" forces you should "dry sump" it. On our race Triumphs which spend a lot of time over 8,000 RPM and corner on soft, slick (no tread) tyres we use the dry sump method. Two oil scavenge pumps, one at the front and one at the rear of the pan, a remote oil tank with combined de-aeration properties, and a pressure pump.
I saw one on Ebay USA last year, and thought about it, but after asking on the forum (check the archive - maybe in MGB too), I decided against it.
Like Barney says, it's alright for a thrashing race engine that will be rebuilt every race or two.
However, for a normal car, it can cause damage (apparantly) to the engine as it stops some of the lubrication that is caused by oil slasjhing and spraying around getting to where it should go.
This thread was discussed between 19/05/2008 and 20/05/2008
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