Frantz On Motorcycle

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Mar 5, 2006
If a Frantz bypass filter is installed on my 83 BMW motorcycle, do I need to worry about oil from the Frantz draining into the crankcase? The BMW has a 2 liter sump. I am afraid that if the bypass filter drains into the sump when shut off, it might be seriously flooded during start up. The Frantz filter must be mounted above the crankcase.
That's a good question. I had an 84 R100 and personally never saw a need for a bypass filter. I put 125,000 trouble free mile on that jewel before I sold it.
Yeah, good question. If there's a way for air to get into the filter housing, it's going to either drain forward or backward.
Why not add two check valves (one upstream, one downstream)??

The spring holding the check ball in place should be enough to prevent siphoning of the oil from the filter. I have one of these with a 6psi cracking pressure. I was going to use this on my bypass to prevent oil starvation at start up, but decided it wasn't needed with further research.

6psi should be enough to hold a siphon.
Even .5 - 1psi cracking pressure should do it. Even if it doesn't completely, it will, at some point, manage to contain most of the mass. Much depends on how the lines dip and up turn as well as the filter's elevation above the "drain plane" (either forward or backward). Eventually you should get a vacuum'd column of oil with a slight air gap that can't travel past the upturn in the dipped line.

You can go the check valve method, but if you've got enough flexibility to run the lines a bit below the sump, you may be able to avoid spending the money. Air will travel laterally, it will just compress itself to one very long shallow bubble, but it can't travel down into a liquid where the liquid has to be lifted against gravity ..and the bubble must pass through it.

I don't know if I'm describing this well.
Since Frantz filters mounted "can" end up don't drain until you crack the seal and let air in, you should be fine.
I dunno (as in help me out here)
. I know Ralph and others mentioned that this is a way to save some oil by cracking it ..but..

Both fittings are (typically) on the bottom so that the handle is on top. If either line can get exposed to air (drain), then it should allow the Tp roll to drain one way ..and the center well to drain the other way (once enough air is present to allow the vacuum to be overcome by the oil mass). Now it may be darn difficult (maybe impossible) for the oil saturated tp roll to pass air, but I can't see it not happening otherwise. It may take longer in time than most people leave the thing idle. That is, it's started before the process can occur.
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