I have a bmw r1150gs 2000 that when I travel over 80mph the oil filler cap and seal blow off, have replaced seal and cemented in place but same problem occurs.

I have a BMW r1150gs 2000 that when I travel over 80mph it blows the oil filler cap and seal off?? I have a BMW r1150gs 2000 that when I travel over 80mph it blows the oil filler cap and seal off??

You have a blockage between the inner and outer and inner rear crank seals. If the outer seal is driven in too far it blocks the vent hole and the crankcase can't breath. On the down stroke the pistons will pressurize the case and cause oil to blow by the rings. The drivetrain will need to be removed to access the seals. If you are not experienced in mechanical work, I would suggest that you have this done by a professional mechanic, familiar with this model. You have a blockage between the inner and outer and inner rear crank seals. If the outer seal is driven in too far it blocks the vent hole and the crankcase can't breath. On the down stroke the pistons will pressurize the case and cause oil to blow by the rings. The drivetrain will need to be removed to access the seals. If you are not experienced in mechanical work, I would suggest that you have this done by a professional mechanic, familiar with this model.