johnh wrote:
So full circle really. It tells you to do what I used to do – and might again if I fly another Rotax. It contains mysterious words about maintaining compression but it doesn’t specifically say to hold the prop at the point of maximum compression. Shame, because that was a good hint. I’m surprised the instructors I was flying with hadn’t heard about that.
It actually does clearly say that in my operator’s manual – see a screenshot below. This is the Rotax 912i series operator’s manual revision 1 from 2019.
For me, maintaining pressure can only be achieved by holding the prop whilst a piston is at TDC otherwise you are releasing pressure…..
Silvaire wrote:
Can you safely start a Rotax 912 without clearing the crankcase of accumulated oil after an extended shutdown? I’ve flown them a bit but never dug into this.
Good question and the honest answer is: I don’t know. My only exposure to Rotax engines was in the P2006T twin and we always ‘burped’ the engines. The line I quoted comes verbatim from the Tecnam POH.
LeSving wrote:
There’s room for interpretation perhaps, word by word it only says the operating media (oil) must be observed. This is followed with a procedure for how this is done in the engine.
Perhaps they are saying they want you to check the oil level any time you shut down the engine (i.e. standard aircraft practice) but do not wish to tell you directly that to accomplish an oil level check the engine must be ‘burped’ every time, in every circumstance – because while it might be a good idea it’s obviously unnecessary if the engine was shut down for only a minute. The question remains as to whether you risk damaging the engine if its started from cold without burping, after it has ‘wet sumped’ but with adequate total oil volume. All of this is made more unclear by poor written English so for clarity it might be better to read it in German.
There’s room for interpretation perhaps, word by word it only says the operating media (oil) must be observed. This is followed with a procedure for how this is done in the engine. There’s no other way to do it without starting the engine, which is a bit like checking if you have (had) enough fuel for the trip after you have landed.
Rotax have had problems with aircraft manufacturers making up their own procedures which do not adhere to the official specs and procedures by Rotax, as well as omitting stuff. Therefore you can read this in the beginning of the manual (my bold):
The purpose of this Operators Manual (OM) is to familiarize the
aircraft manufacturers installing this aircraft engine with operating instructions and safety information.
This document is not intended for use by end customers (private aircraft owners, flight schools…) for operating the engine.
Due to various executions of engine installations, only the aircraft manufacturer is able to provide end customers with operation and safety information tailored for a specific aircraft.
Nevertheless, all provided information in this Operators Manual
(OM) (such as operating limits, safety information, operation instructions…) must be adhered to. The aircraft manufacturer is
obliged to forward this information to the end customer in an
appropriate way (e.g. within the aircraft specific Operators
Manual (OM)).
LeSving wrote:
It’s in the same page (oil level check)
I can only find a “NOTICE” about using the correct oil quantity, not about the burping procedure itself. Not that I doubt it is important.
It’s in the same page (oil level check)
LeSving wrote:
Who knows, but the procedure is marked with a “NOTICE” in the manual. A “NOTICE” in Rotax manuals means “Identifies an instruction which, if not followed, may severely damage the engine or could void any warranty”.
I don’t see that marking with the “burping” procedure. On what page in the manual?
slight thread drift 
@gallois, I was taught this as well, and OTOH different by others.
So, once upon a time, I went and paid a visit to Lycoming whilst at Oshkosh. I spoke at length to one of their technician about different stuff, and I’m just repeating what he told me. And which also makes sense to me.
Of course, searching the subject online will reveal a lot of reasons to pull the prop thru a few blades prior to starting, but most arguments are just moot, or plainly wrong.
Talking about cold weather starts, Lycoming has published some guidance in Operating in Cold Weather.
One of the main maintaince guru’s in my home recommendeds cracking the engine and then flicking the ignition switch on when oil pressure starts to show.
Something to do with cavitation in the oil pump
I have to admit on the first flight of a cold day even on twins I have been turning the prop before start up. This was suggested by various mechanics and we have never had any problems because of it.
