912 unloaded

[facthunter]

I never suggest ignoring the manufacturers advice but it's not a bad idea to appreciate the principles behind it as well and some times you have to adapt to circumstances that are not ideal.. Nev

[Thruster88]

45 minutes ago, IBob said:

With respect, Thruster, I'll be an old wife and take the manufacturer's advice, rather than yours....)
 

When fitting an overhauled cylinder on a lycoming engine the hydraulic lifters are installed "dry" so the dry tappet clearance can be measured.  The collapsed "dry" clearance must be between 30 and 80 thou. There are different length push rods to get this correct.   After starting the engine said hydraulic lifters pump up with oil pressure. The rotax may be special and different but I doubt it. 

 

The biggest risk in relation to oil for the 912 is not air getting in the lifters,  it is the fact that the engine must suck oil from the remote tank. If the oil pump loses prime doing this the engine will be xxxxed,  the lifters will be fine, that should be the new wives tale.

Edited July 30, 2022 by Thruster88

[facthunter]

It's better to pump them full of oil before starting the engine then the lift will be less sudden and you won't have clattering noises. The biggest issue is to have the pressure pump primed and no air coming through the line to it . Monitor "oil pressure rise" on engine start. Nev

[BrendAn]

3 minutes ago, facthunter said:

It's better to pump them full of oil before starting the engine then the lift will be less sudden and you won't have clattering noises. The biggest issue is to have the pressure pump primed and no air coming through the line to it . Monitor "oil pressure rise" on engine start. Nev

How are you priming it. Do you mean spinning over for a few seconds with the mags off.

[facthunter]

Fill the tank to normal position and bleed the suck line near the motor to remove the air without the oil draining out.  Compressed air will increase the flow. Overflow  pipe position  is suitable to apply a few Lbs pressure. . Nev

[BrendAn]

14 minutes ago, facthunter said:

Fill the tank to normal position and bleed the suck line near the motor to remove the air without the oil draining out.  Compressed air will increase the flow. Overflow  pipe position  is suitable to apply a few Lbs pressure. . Nev

Ok. Makes sense.  My oil lines are fairly long too. The oil tank is behind the passenger seat. Jabiru lsa  55.

[Thruster88]

12 minutes ago, BrendAn said:

Ok. Makes sense.  My oil lines are fairly long too. The oil tank is behind the passenger seat. Jabiru lsa  55.

See my post above

[BrendAn]

6 minutes ago, Thruster88 said:

See my post above

Thanks thruster . I did read your post and what you say is even more important with such long oil lines.

[Blueadventures]

One thing I do is burp the engine to put its oil into the can, check that level on the dip stick, should be between the low and high mark.  Note this level.  Now when I change oils I empty into a graduated container.  Then what ever the amount taken out is what I put back in; that way the level is the same.  When changing the filter (I do every second oil change, I add an extra 100ml of oil and put a little oil in the new filter.  Can not go wrong this way.

 

About a year ago a friend was doing an oil change and I happened to be there after he started.  He put on new filter and added 3 litres of oil when he pulled the engine through pre start oil poured into the cabin, it was a lightwing and the oil can is on the cabin side of the firewall.  oil poured out of the can onto the cabin floor.  Reason was the sump still containing oil as he didn't burp the system; had he adopted the method of measuring the oil amount taken out he would have seen something wrong before he put the new oil in.

[pluessy]

I also crank the engine with one set of spark plugs removed (caps grounded or ignition off) until I have positive oil pressure on the gauge. This way the engine (and starter) has no load and you can crank it for 10-15 seconds without overheating the starter motor or the engine firing up and running without oil pressure. Standard practice for every rebuilt engine and should be done on the Rotax whenever the oil lines have been opened.

Burping the engine before draining the oil is also standard practice. If you don't understand the oil system on the 912, read the manual. The way Rotax designed the dry-sump system for the 912 is quite different (unique) to most conventional oil systems, dry or wet sump.

[Thruster88]

Just on the old wives tale about air getting in the lifters, what happens to the air in a new oil filter?

[IBob]

16 minutes ago, Thruster88 said:

Just on the old wives tale about air getting in the lifters, what happens to the air in a new oil filter?

It is passed through various of the lubricated parts of the engine as you rotate by hand the prop for approx. 20 engine turns.

So completely refilling the entire oil circuit.

As stated in the manual.

[RFguy]

OMG ! RUNNING WITHOUT A PROP ?    NO NO NO !

I would NOT (and rotax does not) recommend running the ROTAX without a minimal inertial  mass moment . 

NOT ONLY DO THEY NOT RECOMMEND IT, they forbid it

HERE ARE THE NUMBERS !!!!. 

 

 

Inertia for a thin disc  = 1/2 . m . Radius squared. ..

soooo for a 25cm radius disc, it must weight a minimum of 4.8kg 

Made of aluminium sg = 2.7 g/cm2, that is 1777cm2, or a 25cm radius disc that is 0.905cm thick.

for say 30cm radius (60dia) , that is a 3.3kg disc, and the disc for ally will be 1234cm2 and 0.436cm thick.

So if you go with something like 5mm plate, 60cm diameter, that will work.
or 10mm plate,48cm dia, , that will work... 

In gold, 25cm diameter,  4.8kg, 248cm2, or 1.26mm thick but it might not hang together, without being some gold alloy. 

The rotax has a minimal flywheel, also. 

 

 

Edited August 11, 2022 by RFguy

[pmccarthy]

Gold would hang together just fine. It is quite strong.