912- Getting oil back into circuit/filter after oil change

It doesn't matter to the engine, cap on/off but you may not hear the "burping" if the cap is on.

The burping signifies that most of the oil in the crankcase has been returned to the oil tank/reservoir - continuing to turn the engine by hand will circulate oil from the tank ,through the oil cooler and the oil filter but very slowly.

Burping, pressurised air escaping from the crankcase via the oil return tube, will continue as long as your rotate/crank the engine.

In the previous oil filter it had a check valve in it and you couldn't pre-fill so you rotated the prop to help fill it after you installed it. These newer ones can be pre-filled. I can fill it to the top three times and let it soak and disperse into the canister and then still put it on without losing any oil. It was more important back with the older filter to get oil into the dry filter so you rotated the prop to help fill it. If you pre-fill the filter now then you've done the same as rotating the prop.

Hi All

I agree to a point with Rogers view, if you pre-fill you reduce the air volume trapped in the system before you start.  The way to clear it is turning the prop, slowly allowing the blowby gases to push oil from the block to the oil tank.  The idea of removing the oil tank cap is simply so you can hear the burb of air when you have cleared any oil puddle from the bottom of the "dry" sump of the crankcase.  Given the crankcase vents at the tank cap area there is no change as to how the pumping of the oil circuit is done, it is just for ease of verification.

With that said the turning of the prop still has value in that we should clear as much air from the oil filter as possible to not trap any within the valve lifters.  The valve lifters are the most sensitive to air getting caught within the internal galleries and leading to bounce until they can pump up.

In short, pre-oil the new filter, install.  After that turn your prop to clear the balance of air.  The oil tank cap off just helps you determine when the case is passing more air than oil, we know by the burb in the tank. This also primes any small voids that may have occurred within the pickup line to your oil cooler as well.  

Cheers

I believe that turning the prop is not about getting the crankcase (ring blow by) pressure to make the oil tank 'burp' rather it is to manually turn the oil pump (s) (two on a 914). 

While with the spark plugs removed, you can turn over the engine more easily or as directed by iRMT class, you can use a starter 'hot wire pickle' to engage the start motor. 

Post hose change, or if you didn't keep that oil tank 'out' hose elevated during the tank removal and cleaning, a purge may be in order. 

I retained one of my old oil tank hose (metric swivel) fittings to make an oil tank shop air pressurization (8-10PSI) for expediting purging. Again, as instructed, by pressurizing the oil tank (and thus the lubricating system) it will compress the air bubble in the system, making it smaller, and easier to pass. 

I was also taught to prefill the hoses and oil filter where possible. 

Did Dean mention that these engines hate oil starvation?

Please, I encourage anyone to comment and 'set me straight' as the last thing I want is to A) give bad information leading to oil starvation or B) get confused on my understanding and cause my own oil starvation situation...

Happy motoring!

Cheers! 

Below is a Rotax-Owner video demonstrating how to perform the oil check and oil change procedure on the Rotax 900 series engine.

Oil level check:  https://www.rotax-owner.com/en/videos-topmenu/expanded-video-instructions/36-exp-si-27-1997

Oil change procedure: https://www.rotax-owner.com/en/videos-topmenu/expanded-video-instructions/39-exp-si-27-010