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Author Topic: BMW R90/6 Cafe  (Read 13969 times)

Offline ncologerojr

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Re: BMW R90/6 Cafe
« Reply #220 on: May 17, 2019, 10:52:40 »
Just asking myself the same question.  If there's no air in the pipes, it could work. I'd prefer to see it higher than the master though.
Is the reservoir lower than the master cylinder?  Will that work right?

Great question. A reservoir does not “need” to be above the master cylinder. In theory, there should be zero air in the system so it doesn’t matter. I believe that it is usually placed above as precaution, so if air were to get into the system it might make its way up to the master cylinder.

My reservoir is actually just about level, however the clear tygon hose loop is well above the master. If air were to get into the system, the highest point is that hose loop where it would be clearly visible.

I have a great motorcycle museum nearby, and I actually noticed several race bikes with a lower reservoir which made me consider the whole theory.

For an everyday rider just racking up miles between servicing, put the reservoir at the top.


Online irk miller

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Re: BMW R90/6 Cafe
« Reply #221 on: May 17, 2019, 11:28:30 »
Great question. A reservoir does not “need” to be above the master cylinder. In theory, there should be zero air in the system so it doesn’t matter. I believe that it is usually placed above as precaution, so if air were to get into the system it might make its way up to the master cylinder.

My reservoir is actually just about level, however the clear tygon hose loop is well above the master. If air were to get into the system, the highest point is that hose loop where it would be clearly visible.

I have a great motorcycle museum nearby, and I actually noticed several race bikes with a lower reservoir which made me consider the whole theory.

For an everyday rider just racking up miles between servicing, put the reservoir at the top.
You're overlooking an extremely important point.  Brake fluid is hygroscopic, which means it attracts water.  Moisture in brake fluid creates gas bubbles when your rotors get hot.  Those gas bubbles will get trapped in high points and cause your brakes to get soft.  This is why a reservoir is above level and vented.  Comparing it to a race bike is a mistake, since the systems have completely different maintenance cycles and engineered parameters.

Offline ncologerojr

  • Posts: 827
    • Catskill Mtn. Customs
Re: BMW R90/6 Cafe
« Reply #222 on: May 17, 2019, 11:56:48 »
You're overlooking an extremely important point.  Brake fluid is hygroscopic, which means it attracts water.  Moisture in brake fluid creates gas bubbles when your rotors get hot.  Those gas bubbles will get trapped in high points and cause your brakes to get soft.  This is why a reservoir is above level and vented.  Comparing it to a race bike is a mistake, since the systems have completely different maintenance cycles and engineered parameters.

Sorry, I didn’t overlook that point I just didn’t want to get too into the weeds while typing on my phone. I just simplified and said “if air gets into the system it makes its way up to the reservoir” I didn’t feel like I needed to address exactly how gas ends up in the system.

 As I said above, a regular bike just racking up miles between servicing (maintenance cycles), put the reservoir above the master.

This is not a daily-rider bike, it will see few miles. It’s going to need regular servicing with those miles. This is a non-vented Brembo reservoir, and the clear tube serves as a high point in the system. Gas build up will be visible and easily managed.

Offline ncologerojr

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    • Catskill Mtn. Customs
Re: BMW R90/6 Cafe
« Reply #223 on: May 18, 2019, 01:30:10 »
Final polish on the fairing.


Offline canyoncarver

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Re: BMW R90/6 Cafe
« Reply #224 on: May 20, 2019, 16:10:50 »
Beauty!