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Oil circulation


Active Member
I've experienced numerous delays in my 12iS build, some of which are even my fault. :). I have the engine hung and plumbed and am wondering the best way to periodically circulate the oil. I can easily jump the starter with an external 12V battery and would 'burp' the oil system first. My questions are:

1. Is it better to do so with the spark plugs in or out? I would think relieving the compression would allow the Rotax to build oil pressure easier and faster. However, I am unsure if the lack of compression returning oil to the tank is a problem.

2. Would you use an engine fogging oil sprayed into the cylinders before spinning the engine?

Thanks in advanced for any responses.
just burp the thing, by hand. Plugs in. No turning with the startermotor. Just easily move the blades, slowly when pressure builds up. That way the oil gets the quickest way back to the reservoir.
Of course (when it's finished) flying the lot might be even better...
The oil will NEVER burp if the spark plugs are removed. Air that leaks past the piston rings pressurizes the crankcase to force the oil out to the external tank.
What's the motivation for circulating the oil periodically? If it's for corrosion prevention, you can rest easy as the materials inside of Rotax engines are significantly more modern than legacy engines, and don't require upkeep sitting out on the ramp.

First look up "Purging" in this forum -- it's different from routine "burping" and must be done before starting; you'll find links to Rotax videos and a Service Instruction describing how to do it. You'll also see comments about hazards of using the starter to turn over a 912iS engine, which might damage the ignition coils if the plugs are disconnected.

Purging gets done with at least 1 spark plug removed from each cylinder, so the engine turns easily. Oil return to the tank is moved by the oil pump.

I'm just wrestling with this myself.