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Join Date: May 2008
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912s hard starting

05/10/2008 7:06 PM

We are looking at purchasing a 912s rotax motor for our aircarft, around here they have been having trouble starting them from cold. It appears that it is kicking back against the starter. (we are using 95 octane) Standard 912 starts fine.

Bob

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#1

Re: 912s hard starting

05/11/2008 3:31 AM

Check your timing. 95 burns too slow. Try a mixture of 50/50 with 87. This might give you the proper burn with the added properties of the 95.

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#2

Re: 912s hard starting

05/11/2008 9:39 AM

Ron 97 is stated as minimum requirement for the S version so it would not hurt to get a fuel that is slightly higher in octane.

As far as I can tell the AKI 87 is LOWER in octane than the RON 97 so I am at a loss as to why other post mentions mixing your 97 with AKI 87

Your S version has a higher compression ratio and may start a bit harder but it should not have real problems. It cannot hurt to check the basic settings.

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#3
In reply to #2

Re: 912s hard starting

05/11/2008 1:06 PM

Octane is a function of burn speed. The higher the octane number the slower the fuel with burn in the cylinder.

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#4
In reply to #3

Re: 912s hard starting

05/11/2008 1:30 PM

I am sorry but your point is very badly put.

Octane rating is a direct percentage of straight-chain alkane with the chemical formula CH3(CH2)6CH3 in the fuel mixture. This rating is the measure of protection against self combustion or detonation under pressure, not the burn speed. In an ignition dependent combustion engine, the ignition is meant to be controlled by timing and any detonation or self combustion before this point is detrimental to the engine and its performance.

Ron 97 has an octane percentage of 97 whereas AKI 87 has an octane rating of 94. The lower the octane rating the worse your self combustion problem will be and the engine can start pinging which is bad. If the manufacturer says to use minimum RON 97, there is no point at all to mix this fuel with one of a lower rating.

Look it up on google and you will find that I am right.

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#6
In reply to #4

Re: 912s hard starting

05/11/2008 11:32 PM

Why do you argue with me rather than fix the problem with the original post. If you are so smart fix IT!

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#12
In reply to #6

Re: 912s hard starting

05/12/2008 10:12 AM

I don't think he is arguing with you, just explaining, to the point, of exactly what the differences in octane rating are and how they likely would affect engine performance. The question I have is, because this is a cold starting issue, does octane rating affect vaporization rate. If so , and IF 87 vaporizes faster in very cold weather starting conditions (I don't think so), would it be allowable to start the engine on 87 and switch after a low speed warm-up. This might require a second very small fuel tank. In racing, they use octanes of 103 to 117 or so, depending mostly on RPM range. A fuel supplier told me that in addition to controlling flame front propagation, high compression racing engines that live at 6000 RPM's and up require a faster vaporizing fuel to eliminate droplets that also lead to detonation. Of course, these formulations cost money (3 to 4 times the cost of pump gas) and aren't readily available on every street corner. For small, recreational aircraft use, purchasing a couple of 30 gal. cans of Cam 2 or VP (Vels Parnelli) or Sunoco or other racing fuel isn't difficult. I don't think it hurts an engine to use a higher octane fuel than required. And racing fuel burns cleaner as well as a hole in your pocket.

Here, in winter, we sometimes use a fuel line anti-freeze (methanol). I have found that when I use it, 0 deg F starting seems a bit easier, but then I don't have a high compression engine to worry about. I always carry a can of starting fluid (ether) just in case I sense flooding or just don't want to wear down the already half frozen battery and save wear on the starter. I even installed a two foot piece of 3/8" PVC extending from the front grill into the air intake duct so I don't have to open the hood. I know that high compression engines and ether don't get along well. You should never use it on an all out race engine although the NASCAR guys will use it to get re-fired during a race where everything is on the line.

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#13
In reply to #6

Re: 912s hard starting

05/12/2008 12:08 PM

By giving correct replies to wrong answers I AM HELPING original poster.

If you dont like to be corrected maybe you should make sure what you post is correct or state you are not sure yourself.

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#15
In reply to #13

Re: 912s hard starting

05/12/2008 3:39 PM

Well put case, I gave you a GA. Your opponent (mayt2u) is totally wrong and off base....basically he has not got a clue!!!

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#14
In reply to #6

Re: 912s hard starting

05/12/2008 3:37 PM

This sort of reply is uncalled for, you described it completely wrongly and could seriously mislead others.

I agree with Case completely (for a change says Case!!)

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#16
In reply to #14

Re: 912s hard starting

05/12/2008 4:17 PM

We have had our discussions here Andy, In the end we either agree or we agree to disagree.

I respect your input as I recognise you tend to know a lot about what you like to post about and you post a lot about what you know.

You are right there are some people who forget that information is just too easy to obtain these days and will stick their NOSE in too soon.

Keep up the proper written language now, no foulmouthed insinuations here please

Thanks for your support, much appreciated.

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#18
In reply to #16

Re: 912s hard starting

05/13/2008 5:45 AM

You deserved support in this particular case, I gave it.....its that simple.

Have a great day.

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#25
In reply to #4

Re: 912s hard starting

05/13/2008 2:35 PM

Not to mince words but Octane rating is not percentage of isooctane. Isooctane is merely the std that is "set" to 100 octane rating. Fuels with 100 rating are still very diverse mixtures, but have detonation character same as iC8.

More detail from Wiki http://en.wikipedia.org/wiki/Octane_rating

Octane number is the number which gives the percentage, by volume, of iso-octane in a mixture of iso-octane and normal heptane, that would have the same anti-knocking capacity as the fuel which is under consideration.

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#31
In reply to #25

Re: 912s hard starting

05/14/2008 1:00 PM

I knew you would say what I meant

I used wiki for that one as well and translated from Engrish to Dutch back to CR4 talk. Sorry about that.

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#5

Re: 912s hard starting

05/11/2008 4:48 PM

It does not appear to be fuel as does the same on av gas. It seems as if the engine is to far advanced a LAME has set it up to the specs still does it.Have even installed a higher capacity starting moter to wind over faster. Starting to think it has something to do with ignition system.This does not happen on mates 912 starts instantly.

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#7
In reply to #5

Re: 912s hard starting

05/12/2008 1:26 AM

Odd problem, I would think it would be worse when hot rather than cold. Personally, I'd check spark plug gapping. If that's ok, I'd set the timing back a bit and see if the problem went away. Does a Rotax use mechanical or electronic ignition? If mechanical you may have a jammed centrifugal advance. Or the same thing in the electronics. This will cause it to be over advanced while starting but be ok while running. A bad vacuum switch might be a possibility.

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#8

Re: 912s hard starting

05/12/2008 1:36 AM

I have worked on a few 912 and 914s. Most of them have to meet a certain rpm and oil pressure then the ignition will fire. plus leading to the fact that usually aircraft batterys are ususally on the small side add cold weather and it makes it hard to start. so make sure your using thick starter cables and a charged battery, you can usually tell because adding a second battery usually starts them up.

also join rotaxengines-list on this site http://matronics.com

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#9

Re: 912s hard starting

05/12/2008 1:40 AM

Hi Guy's, As an old A&P, I would check the mixture first. Then carb. pop off pressure, if applicable. An old trick when all else fails, is to flood the eng. Then use the "starting a flooded eng. routine" in the manual for that eng. If it does't kick after it clears, You know it was lean.....Jay

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#10

Re: 912s hard starting

05/12/2008 9:37 AM

As with any engine, if it kicks back while staring, it is generally a problem of ignition timing.

Any engine will start on the wrong Octane with no problem if all other points (pun intended!) are otherwise correct. Running on a lower Octane is of course another matter....

Having an over advanced ignition (which is similar in effect to a too low Octane fuel) can lead to mild or worse overheating as well as higher than normal wear on certain parts......its certainly not to be recommended.....so take the problem really seriously.

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#11

Re: 912s hard starting

05/12/2008 10:09 AM

First: Gasoline 'octane number' is a measure of the resistance to 'knocking' or 'pinging'--the audible explosion of the residual unburned fuel/air mixture after part of the fuel charge has burned normally.

Kick-back against the starter is caused by the ignition spark happening too soon. If the basic timing is correctly adjusted, I suggest you contact ROTAX and see if they have encountered this before and see if they have a 'fix.' Simply retarding the basic timing may reduce the power output of the engine and overheat the exhaust valves.

There are 4 different methods of measuring the knocking tendency of gasoline fuels.

The Research Octane Number is measured in an ASTM Research Knock Engine which runs at 600 RPM and intake air temperature of 122F. It is designed to simulate light load 'cruising' conditions of automobile engines--and gives a higher number than the other test methods. It is not a good measure for high engine loads. The measured RON of the fuel is actually the percentage of Iso-octane in Normal Heptane that matches the knocking intensity of the fuel being tested. The technician adjusts the compression ratio of the engine to get a 'standard knock intensity' as measured by a knock meter, then adjusts fuel-air ratio to maximum knock intensity, readjusting compression ratio and fuel air ratio as necessary to maintain the standard knock intensity. Ignition timing is fixed and does not vary with compression ratio. Then blends of the reference fuels (iso-octane =100 O.N, and Normal Heptane =0 O.N.) are prepared that 'bracket' the test fuel knocking intensity at the same compression ratio. Simple interpolation between reference fuel knock intensities calculates the test fuel 'Octane Number.'

Motor Octane Number is similarly measured using reference fuels, in a different, though similar test engine. The Motor Method engine runs at 900 RPM, ignition timing varies in a fixed amount with compression ration, and intake mixture temperature is heated to 300F, coolant the same at 212F. This test method is designed to simulate higher loads during acceleration or high speed driving., and results in a measured 'Octane Number' somewhat lower than the Research Method.

The Anti-Knock Index posted on gasoline pumps in the U.S. is a simple average of the Research and Motor Octane Numbers of the fuel. Typical US gasolines with a AKI of 92 will have a Research ON of 96 and a Motor ON of 88, though these will vary somewhat.

Airplane piston engines have different knocking characteristics than automobile engines and fuels are tested using two other test engines and methods--Avaition Method and Supercharge Method.

The Aviation Method, designed to simulate an aircraft engine during cruise conditions--lean 'best economy' fuel-air mixture, high, but not maximum power output--uses an engine similar to the Motor Method, but running at 1200 RPM, hotter intake mixture, higher coolant temperature. High octane aviation gasoline will have higher anti-knock performance than the highest octane reference fuel (100), so tetra-ethyl-lead (TEL) is added in precise amounts to the iso-octane. The Performance Number, which represents the maximum power output of the test fuel, is measured against the TEL-isooctane blend. Experiments were conducted to determine the power outputs of different TEL-isooctane blends under 'cruising', and the Performance Numbers are the test fuel power output relative to iso-octane. A \Performance Number of 110 means the fuel will deliver 110% of the power of iso-octane at the operating conditions of the test engine.

The 'Supercharge' test engine is similar, operating at 1800 RPM, hotter, and uses compressed air to 'supercharge' the intake air pressure to simulate high performance engines. Some highly developed engines operated with up to 3 times normal atmospheric pressure (+30 psig) intake pressure. In this test method, the objective is maximum achievable power output--to simulate take-off and climbing conditions.

An aviation gasoline thus has 2 anti-knock ratings such as 80/87, 100/130, 115/145--the 3 grades available today. There used to be a 90/96 grade also.

The point of all this discussion is to help the readers appreciate that aircraft engine service is much different than automotive service. Power loadings,even in cruise conditions may be 75% of maximum power, and during take-off and climb are held at 100% for many minutes. Another difference is one cannot hear fuel knock over propeller noise. Thus, fuel knock that starts out as mild detonation (pinging) will quickly progress to pre-ignition (igniting before the spark) which will cause catastrophic engine failure in short order.

Because of the danger to life, it is vital to avoid combustion knock in aircraft engines. The manufacturers have spend thousands of hours testing the engines with different fuels under different conditions to ensure safe and reliable service. When an owner/operator deviates from the proscribed operating conditions, he/she becomes an unwitting test pilot/engine designer...with all the risks and none of the expertise usually employed.

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#17

Re: 912s hard starting

05/12/2008 9:24 PM

Sorry boliver, yet wanted to help. Up North we mix all kinds of fuel to get things to run in the cold. We don't have the luxury of having the best temperature in the Southern US to do our testing, just the Great White North. We have engineers that quote scales, charts and other dibble, that one wonders if they really know what they are talking about or just like to hear themselves talk.

Best of luck on the situation and I will no longer subscribe to CR4 if is this the kind of treatment I will receive.

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#19
In reply to #17

Re: 912s hard starting

05/13/2008 5:47 AM

My impression is that you can "give it", but not "take it".

If true, then CR4 is really not for you at all.....you have to be able to "give and take" on CR4.....

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#21
In reply to #19

Re: 912s hard starting

05/13/2008 8:17 AM

Why do you persist in antagonistic remarks?

What purpose or benefit is it to this thread?

Grow up... or start acting your age.

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#22
In reply to #21

Re: 912s hard starting

05/13/2008 8:35 AM

I don't see anything antagonistic in Andy's reply. The nasty remark came from other poster first in reply to a simple correction on his answer. Nobody here said anything antagonistic except for him.

Please don't try and pull this thread out of context, there are many engineers here on CR4 and most know what they are looking at. If you make flaming remarks without due reason you will get rough handled, simple.

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#23
In reply to #22

Re: 912s hard starting

05/13/2008 9:12 AM

Thanks for the support Case and the sensible comments.

I was not planning to react as the remarks were just from a Jest/troll that I mostly ignore completely, so they are more like "water off a Duck's back" for me....

He (or possible she!) obviously does not fully read or fully understand what he/she reads, but thanks for your kind words anyway......

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#24
In reply to #22

Re: 912s hard starting

05/13/2008 9:34 AM

LOL at the rough handling Is this the wild west?

I will hold by the antagonistic assesment. Am I in for "rough handling" for percieving the comments as such?

Yes HT (I cant recall the fellas name from Alberta) did offer incorrect assistance. Yes, he did react badly to being corrected (in a polite manner IMO) to this.

He also appoligized somewhat to the OP and tried to move on with a parting shot at engineers. (poor form)

BUT, persisting in posting in response to him with inflamitory remarks such as You dont belong here.. is not constuctive in the least. He was set straight, he realizes his information was incorrect/incomplete, and has been duly chastised for this. Persisting with those followup remarks adds nothing constructive to this thread, and only makes the person making them look just as much the ass IMO.

My final 2 bits.

(I was the guest poster posting before I logged on this morning.)

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#26
In reply to #24

Re: 912s hard starting

05/13/2008 2:51 PM

"Somewhat" is simply not enough....to my mind, even "somewhat" was being overly kind...he had appalling manners, he is not needed if he is that sensitive to reaction to his own bad manner(s)....

Also we have wasted enough time on him already, he was not worth it....which is why I did not react first to the Troll (you?)....somebody else (correctly!) did!!

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#27
In reply to #26

Re: 912s hard starting

05/13/2008 2:57 PM

I had a hard time understanding the gist of your post.

As for "appalling manners" your little "you stick your Dick out wrongly, we cut it off for you!!!" comment was appalling and unprofessional IMO.

You could use a serious dose of manners yourself.

You calling me a troll?!? LOL That actually made me laugh.. thanks!

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#28
In reply to #27

Re: 912s hard starting

05/14/2008 6:11 AM

Try following the whole series in a logical and timely manner, in the sequence they actually occurred, you will soon see what/who was unmannerly first.

Jumping about like a fart in a tank proves nothing at all....

If you logon as guest, do not expect your opinion to be as acceptable on CR4 as if you appear with a logon name.

Often it would appear that guests "argue" with themselves and 90% of the time at least, only want to provoke....as was the case here......

But who knows which guest is which, only the people who wrote the sentences themselves.....a totally useless exercise if you ask me......

The current terminology for people who appear as guests on Blogs, as I was recently informed in the last month by another CR4 member is "trolls", I usually call them "jests"......

I also find that if you pick holes (easily done most times) in what guests have to say, they either disappear or eventually reappear with a proper name as you appear to have done!!! Both actions are good and fully acceptable to most members I feel!!

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#29
In reply to #28

Re: 912s hard starting

05/14/2008 7:56 AM

"Mommy! He did it first!!" is no arguement for that sort of language on a forum such as this. He never used profanity or stooped to grade school dick cutting terminology, you did.

I fail to understand the fart in a tank comment.

Wether a person posts on a as a Guest or a registered user they should both be entitled to the same ammount of courtesy and mutual respect. As for provoking, it was not my attention. I was merely sick of your poor manners I saw in this thread and many others. I have been reading these forums on a daily basis for nearly 5 years now and I have seen plenty of this sort of egging on, poor manners and internet bullying.

If a guest poses a valid question makes a valid point is it worth less because they havent registered or logged on? Or in my case merely forgot my password and login information as I rarely post here. I had to get my information reset as I couldn't recall it at the time of my Guest Post.

I get the feeling from your post that you are getting off on this and feel that you are "picking me apart" or humbling me perhaps? Whatever floats your boat old man. Go ahead and pick holes in this too but I hold my assesment that you are an uncouth, vulgar and argumnetative.

Carrying this conversation on with you is a lost cuase and like trying to reason with a block of wood. Feel free to post again and have the last word. You aren't worth my time.

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#30
In reply to #29

Re: 912s hard starting

05/14/2008 8:31 AM

You do not appear to have tried reading the posts in sequence as to who was abusive first. You might also notice that I was not alone either in complaining......

The connotation to a tank was with regard to eccentric thinking processes...

Your last post puts you as the one to complain bitterly in a possible situation for example, where you hit someone in the face for no reason and he gives you two, better blows back in your face.....You will be the one to complain " I only hit once!"......."and not as hard!"

I have learnt a lot in this life, but people like yourself remain a mystery....thank God!

Try using the spell checker as well, it may help you in the future when replying on CR4......

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#32
In reply to #30

Re: 912s hard starting

05/14/2008 1:04 PM

Hey, don't stop now, I just called all me mates and we are sitting around my computer with some beers. Please come back and continue, it was fun

Darn, story of my life missing all the good fights Urmm, sorry meant times

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#33
In reply to #32

Re: 912s hard starting

05/14/2008 1:33 PM

Please, don't egg him on. I'm done with him.

I'm old enough to know better to get into these sort of discussions with forum trolls. You both wind up looking stupid in the end regardless of the circumstances, especially when people like to sit on the fence and just be entertained instead of standing up for what is right.

If you're missing the good fights, why not take one up yourself I'll take your spot on the fence for you.

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#34
In reply to #33

Re: 912s hard starting

05/14/2008 2:01 PM

Yeah, sounds a good idea. Now where has that other plonker gone, I feel like a fight.

Ah well, can't always have it our way, he must have gone.

Don't always enjoy sitting on the fence as you might learn from this place. Often enough entwined myself in a "discussion". Most often better to let it go as you are right, two fight two look like idiots.

You have to forgive Andy though, he is an old hand here and we have seen some rotten trolls now and again. Pure obstruction sometimes and he must be going through a phase of being severely pissed off by it right now. I had one of those some weeks ago and nearly left this forum

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#20

Re: 912s hard starting

05/13/2008 6:11 AM

I have a Hirth F-30 (4 cylinders) and it was nearly impossible to start. I put a centrifugal clutch on it, and it starts right up...and it allow me to idle without the prop turning while on National Park lakes...a big plug around docks.

The torsional resonance between the engine and prop via the rubber donut did not allow the engine to come up to speed. Without the prop engaged in the low frequencies of startup, the engine could function.

The clutch mod cost me around $700.00. It made all the difference for my seaplane...

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#35

Re: 912s hard starting

05/14/2008 6:37 PM

Thanks for input so far it appears that it is not a fuel issue, talked at a local club meeting last night & sugested to start with big battery & calbes as timing is set in factory for these motors.

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#36
In reply to #35

Re: 912s hard starting

05/15/2008 2:05 AM

Do you (or anyone else) know of a way to check that the timing is still right?

Is it possible that someone has accidently, removed/replaced an item that affects the timing?

Is it possible that the "unit" that performs the timing (?) is defective and has lost its method of working properly with regards to an advance/retard mechanism (for want of a better word)?

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#37
In reply to #36

Re: 912s hard starting

05/15/2008 12:59 PM

It may sound strange but I once had a Honda........yes really

It had factory set timing as well by means of the old magnetic pick ups on a disc that was set in the factory with the rotor whizzing past inside it. What had happened was that somebody in the past had thought the whizzing magnets had to touch the pick ups and set them so they actually scrapped the surface. This is wrong of course and there should be an air gap of a given size depending on the make of the unit.

The end result was that the coils had shattered inside without any visible damage to the outside but they now had a "fuzzy" field of pick up strength rather than the accurately determined point they need for proper function. My timing was all over the place and the bike did not run very well if at all depending on the ambient climate at the time.

Maybe your unit has had the same misfortune? Worth a check unless the engine is nearly new.

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#38
In reply to #37

Re: 912s hard starting

05/15/2008 6:01 PM

I gave you a GA.

But you are boring the arse off me with your good answers, can you become "provocative" or something to liven things up?

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#39
In reply to #38

Re: 912s hard starting

05/16/2008 1:58 PM

Shit, thanks you bastard, another good answer!


Provocative enough for you

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#40
In reply to #39

Re: 912s hard starting

05/16/2008 4:05 PM

Perfect you Arsehole!!

100% again.....

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#41
In reply to #40

Re: 912s hard starting

05/17/2008 11:32 AM

You reckon this could catch on?

Well I enjoyed it anyway

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#42
In reply to #41

Re: 912s hard starting

05/18/2008 5:56 AM

I thought it already had!!

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