Turning over Rotax pre start?

[markendee]

Can some knowledgable person tell me the why/why not of turning over the Rotax by hand prior to starting the engine?

 

Many theories but not sure of the correct reason.

 

Any information would be a help.

 

 

[PaulN]

No, I'm not a knowledgable person but I'll stick my neck out.

 

The advice I have been given is that the Rotax gains no start-up benefit from pre-start hand cranking. The only need for hand cranking is during pre-flight checks. For a correct indication of oil level in the tank one should hand crank around 3 to 5 turns until you hear the oil tank gurgle ("burping") to ensure all of the oil is pumped back to the tank before reading the dip stick.

 

From experience I have found the only must do's (must have's) for efficient starting in all conditions is a good sprag clutch, heavy duty starter and a good battery. Until I recently replaced all three of these I used to have all sorts of issues getting the Rotax to wind over and fire up, especially when cold. Now she fires up with just a touch of the start button every time ;).

 

Hope this helps,

 

Paul

 

 

[trevorp]

Not so sure with rotax, but in the jabiru 160, when i asked instructor the need to turn prop at least 4 times, answer was checking compression on each cylinder to see if all the same amount of force required for each. If one was less , suspect valve not seating properly. ie jab230 6 times, 6cylinders. Always check switches are off before turning. Another guy metioned that if you have earth fault you might get ignition, but instructor reckoned you would be battling to pre start a jab 2200 motor by hand even with switches on, dont think i would try that though, but i guess you should treat all with caution. TP

 

 

[Guest pelorus32]

G'day Mark,

 

two reasons on the 912 ULS: The one Paul gave about oil level (the engine has a dry sump) and also to check that the dreaded crankcase problem hasn't happened. In that case the engine is locked up and won't turn because of some movement between the barrels and the crankcase I think. I have experienced this problem with a Tecnam and it's very distinctive. Someone like Facthunter might provide more details of the actual problem with the 912ULS crankcase.

 

Regards

 

Mike

 

 

[facthunter]

Pull through.

 

Sorry mike I can't help you there, but I agree with pulling the engine through pre-flight. If the jab. oil filler cap is left off, you can hear the gasses going past the rings, and you get a feel for whether the compressions are OK. They are better after the engine has run. Recently I pulled a near new (25 hour) 100 hp rotax through to get it to gurgle to check the oil quantity. Because the compression was so good, it took 20 compressions to get the oil to return to the tank, even though I was turning the motor slowly to give it time to leak past the rings. The owner told me it normally takes 50. It's only the blowby gasses that provide the pressure to return the oil to the tank from the crankcase, Clever innit! Nev..

 

 

[Guest TOSGcentral]

Interesting! The question was turning over a Rotax – and everyone jumped onto the 921!!! Sign of the times I suppose!

 

Here are a few pointers for what I do – and why – assuming of course that you have checked that the ignition(s) are OFF and the throttle is CLOSED!

 

• An engine should be pulled through as part of the pre-flight preparation anyway. Why are you doing this?
   
   
  
• Basically to check for compression on all cylinders and any unusual noises.
   
   
  
• The latter gave me the screaming hab dabs the first time I pulled a 912 through – the grating and noises from the gearbox were terrible. Noise = Damage and I feel that is a terrible piece of engineering!
   
   
  
• I know nothing about “gurgles†and all the rest of it. They did not seem to be mentioned in the handbook and nobody had taught me about them – which is a situation most of us are in I suppose when we start something new in this game.
   
   
  
• With the two strokes the situation is far more simple:
   
   
  
• Turn the motor via the prop to check the compression, unusual noises etc.
   
   
  
• On a stone cold motor turn it 10 prop blades. This is because a two stroke is lubricated via the fuel/oil mix and this is pre-lubing the motor.
   
   
  
• On a warm motor do a precautionary 3 blades to check for compression and unusual noised between flights.
   
  

 

Aye

 

Tony

 

 

[Flyer]

I was taught to treat ALL props as live and shaped like an axe. Pulling a prop through was regarded as unneccesary and somewhat dangerous. I also learnt on GA (Piper Warriors) type aircraft.

 

Curious to see people pulling props through and comments like

 

" but instructor reckoned you would be battling to pre start a jab 2200 motor by hand even with switches on,"

 

Scary.....

 

Regards

 

Phil

 

 

[BigPete]

A Jab motor has to be rotated at 300 RPM or more to create spark for the plugs. :)

 

HOWEVER - if the motor has been running and there is a hot spot in one of the cylinders - you may loose a finger or worse...... :yuk:

 

regards

 

 

[trevorp]

Hi Flyer, I to believe you should treat all props as live . I do not turn prop when performing my walk around checks and believe it should only be done by lame or level 2 maitainer with mags disconnected. But seem's with a jab 2200 motor before first start with all switches off, MAYBE ok. I wonder what the Jabiru hand book say's. But for rotax it seem theirs different reasons. Cheers TP

 

 

[facthunter]

Care.

 

In response to flyer , and others.

 

With a conventional engine, with impulse magnetos, at one point the slightest movement of the propellor will cause a very intense spark just at the right time to make the prop. spring sharply into life. Regard the propellor as lethal, in this situation.

 

In a general sense, caution would suggest that anywhere in the prop arc is to be avoided even when servicing, especially if others are working on the aircraft at the same time.

 

Hot spots are mentioned. These can be spark plug electrodes, exhaust valves, or more likely, sharp edges of incandescent carbon, that has built up in the combustion chamber.

 

After an engine has run, it is possible for it, after shut-down, to burst into life some minutes later. This was more commonplace with notorious overheaters like the Sidderly Genet Major.

 

Magnetos are rendered harmless (hopefully) by earthing the primary coil. (both ends) as one end is already earthed, (This is how you turn the engine off), OR inserting a piece of insulation preventing the points closing at all, ( maintenance procedure where points are fitted).

 

Those of you who are steadfastly opposed to turning over the prop. let nothing that I say change your mind, because CARE & EXPERIENCE are needed, and if you are not happy DON'T DO IT. Turning the engine backwards reduces the risk but is not recommended where vacuum pumps are fitted.

 

In earlier times, when starters were not commonplace, i n the process of priming and clearing the motor prior to start, you got to check what we are talking about as a matter of course. I regard all of this as familiarity with your aeroplane, enhancing safety when done properly. After all if there is a simple way of detecting a fault that may cause engine failure later, why not avail yourself of it. As in all things you have to know what you are looking for, and how to perform it.

 

With regard to 2-strokes, I regard it as essential pre flight procedure. I've felt some engines that I wouldn't keep running as lawnmowers. Regards Nev..

 

 

[Flyer]

Does the Jabiru or Rotax motor not have impulse mags?

 

I'm showing my lack of knowledge on engine types here...

 

regards

 

Phil

 

 

[Bruce Robbins]

The Jab motors use coils, powered and triggered by the flywheel (Just like the old Victa lawnmower). That's why you have to spin them over at about 300 rpm to generate a spark. Rotaxes similar story, which is why this wouldn't work to well with a Jab motor.

 

[ATTACH]4657.vB[/ATTACH]

 

:;)1:

 

Bruce

 

 

 

[markendee]

Thanks for all the response

 

Thanks very much for your thoughts and advice.

 

Regards,

 

Mark

 

 

[Yenn]

The Jab can be started by hand, but it is not an easy exercise. The person who sold me my Jab 160 has done it and has the missing fingers to prove it. Let me re phrase that, he doesnt have the fingers, about 4 of them. I always pull through and also prime before starting my 2200 Jab, but that is at low speed. If the battery is down a bit the starter spins the motor at what seems enough revs but it will not start so I think it would not start unless you were really trying.

 

 

[HEON]

Read the above with interest as why or why not to turn over an engine prior to flight.

 

With Rotax 914 (assume also 912) it is not possible to check the oil level without doing so.

 

Rotax has a dry sump. The oil is not stored in the engine but in seperate tank which also has the dip stick. On every instalation I have seen including my own it is above the bottom of the engine. Gravity allows some oil from this tank to flow back into the engine when stopped.

 

If you do not "burp"the engine thus pumping the oil back into the tank it will read low. If you add oil to top it up, when started the oil level could well be above the max which Rotax, and most engine makers, do not recommend.

 

This is not applicable to Jab's as they are wet sumped like most cars which require the oil to be allowed to settle via gravity before an oil reading is taken.

 

Regardless of other reasions to do or not to do, not "burping"a Rotax means you cannot know how much oil is in the engine! This has some potential for problems.

 

 

[markendee]

Heon,

 

I couldn't agree with you more. This is the reason given to me for turning the engine over prior to starting.

 

However a mate with a 912 says his dip stick always shows half an inch low and comes up to the correct mark when burped. His reasoning is after standing the half inch low is indicating correct oil level so why go to all the effort?

 

I wondered if pulling it through helped lubricate the engine but can't get my head around twelve or so slow turns doing much of that.

 

What do you think of using the low oil mark as correct?

 

 

[HEON]

Markendee,

 

Why expend the effort? I feel each to his own but I personally would like to know before getting up there as I think I would have great problems doing an in flight oil add dispite being possible in some aircraft (CK Smith's "Southern Cross"comes to mind...but not an SOP even for them!)

 

To lubercate prior to start? If rearly required in modern engines every car would have a crank handle. Now I have (whats left) more white hair than most and I have not seen a crank handle on any car for at least 50 years.

 

As to useing the low mark, again each to his own, but being less adventerous than some I will personally just do as Rotax says and hope they have it right.

 

 

[facthunter]

Returned oil.

 

While the change in level may appear to be pretty constant, there is an assumption that this is the case. The only way to be sure, is to turn the engine, (or start it ) and then check the level. If the tank is overfilled it will vent the extra as the engine "breathes" through the oil tank. (This is the method of returning the oil from the engine which is dry sumped) .... (pretty cheeky eh!) . It also means that you will vent oil any time you are in a negative "G" situation. so don't stay upside down for too long. Turbulence may cause it too. Nev..

 

 

[Kev]

Markendee,

 

Pauln is correct. The reason for turning the 912 by hand is to ensure that the engine is fully scavenged (ie that all the oil is in the tank) before you check the contents on the dipstick. Otherwise, you could get a false reading (ie low) and add oil unnecessarily.

 

Kev

 

 

[Guest Nickjaxe]

Hi guys my first post on this fantastic web site I have just come across,

 

Now this may not apply you guys in hot climates but I live in the UK and we get some pretty cold days,

 

turning the prop before starting, I do it every time I start my rotax 503 from cold apart from checking compressions ect, I do it for ease of starting,

 

The way I do it, normal checks for closed throttles mags off ect, put on full choke prime fuel up and give the prop some good fast turns, my theory is that it draws fuel in to the pots pre lubes the engine and breaks down the friction of the internals from not turning for maybe some weeks,

 

I have tried starting my engine without going through the above but find it starts much quicker after hand turning, its an electric starter by the way and needs to spin quite quick to fire.

 

Nick.

 

 

[K-man]

The Rotax 912 also has a reduction gearbox. This means that it would be near impossible to start by hand. Agree that all props should be treated as live but with the Rotax, turning by hand is required to accurately check the oil level, as pointed out in the earlier responses. So, for all those who do not want to turn the motor over, don't buy a Rotax. For the rest of us, the Rotax is a very good engine for light aircraft. :thumb_up: :thumb_up: :thumb_up:

 

 

[Cosmick]

Why handle the prop.

 

I fly an Aerochute which has a Rotax 503, The training syllabus advises - chokes on, fuel on, prime fuel, Ignition Off - pull the starter 3 times ( or 3x 2 second hits with the electric start). Either way well away from the prop.

 

Then Ignition on ..........

 

May not be suitable for the 4 strokes.

 

I am currently training in a Technam Echo with a 912 and go through the "Burping" procedure as instructed on that type.

 

 

[K-man]

I have friends with 912s who crank the motor a few times without throttle or choke. That has the same effect.

 

 

[philipnz]

Because it's in the engine operation manual. You need no other reason. Furthermore the manual makes no mention of fingers being lost, you will never wind a Rotax over fast enough by hand to activate the magneto's. Nor does it mention winding over a just-shut-down hot engine to check the oil.

 

I can't believe people are suggesting you shouldn't.

 

 

[BLA82]

you will never wind a Rotax over fast enough by hand to activate the magneto's. Nor does it mention winding over a just-shut-down hot engine to check the oil.

 

I can't believe people are suggesting you shouldn't.

I agree in parts with the above as the manual does say for it to be done bt to think you can't start it by hand to trigger the magnetos? I thought that Rotax engines had ignitions similiar to a motorbike and to trust the fact they wouldn't start by hand is a sure way to amputatate some extra limbs.

 

I think the rule is ignition off and treat all props as live by turning them so if you slip you fall away from the prop arc.