DragBikeMike
Serious Thumper
Offline
SuzukiSavage.com Rocks!
Posts: 4406
Honolulu
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I wanted to get a better feel for how much vacuum this thing might pull. The gasket failure didn't seem consistent with such a minute pressure differential. So I cleaned up the area with mineral spirits and smashed a big mound of modeling clay over the leak zone. I really piled on the clay to make sure its was sealed good. I only tested it with the KrankVent installed because I figured vacuum will hold the clay dam in place, but pressure will blow it off. With the leak plugged, it pulled 1.0" Hg vacuum.
These tests were done in my garage. I just started it up and ran the engine unloaded up to about 5000 rpm. I never rode it with the vacuum gage in place. My intent was to ride it, but I found the leak. That shut the test down. For all I know, the blown gasket could simply be a coincidence. The missing chunk of gasket could be inside the engine, or it could have blown out of the engine. I wont know until I take it apart.
Regarding crankcase vacuum and oil pump suction. Yes, I agree, the crankcase ambient pressure on both sides (suction & discharge) should be the same, so the DP across the pump should not be affected. But this little pump doesn't appear to have any suction head at rest, and when the engine is operating, it looks to me like it will go into suction lift because the oil level in the sump will go down. The temperature of the pumpage is elevated, possibly as high as 300 degrees. My concern over pump suction was related to flashing. If the contraption pulled too much vacuum it could reach the saturation pressure of the liquid. I mentioned that it seemed like an unlikely problem, and now that I have a better feel for what sort of vacuum we are dealing with, I'm very confident that pump suction wont be a problem. The oil pressure gage backs that assumption up.
The stuff I've been reading indicates that there are oiling problems associated with crankcase vacuum. Wrist pins and exhaust valve guides can run dry. But those problems don't come into play until crankcase vacuum approaches 10" Hg. This thing isn't anywhere close to that.
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