Primarily for general aviation discussion, but other aviation topics are also welcome.
  • 1
  • 4
  • 5
  • 6
  • 7
  • 8
User avatar
By Miscellaneous
#1787130
lobstaboy wrote:I'm sorry Misc, as far as I'm concerned that just won't wash. I DO want to know exactly how much oil, not simply if there is "enough". Why? Because a change in the oil level that is unusual is an early sign of a problem with the engine.
Rotax 912 and 914 engines are superbly reliable and should use very little oil, as we have said. But to get blasé about it and treat it the way you would a car engine may be expensive and/or dangerous.

Steady on there fella, where's this notion of being blasé coming from? :?

lobstaboy wrote:Why? Because a change in the oil level that is unusual is an early sign of a problem with the engine.

I'm afraid I don't see how that explanation explains why? How is gurgling going to show up an unusual change in oil level? I guess there's an outside chance a catastrophic fuel or water leak in to the engine could result in an unusual reading. But then that would become apparent before take off. From a purely oil related POV gurgling only serves to prevent overfilling.

I have indeed been on the Rotax course, guess what was said about gurgling. But don't you go assuming that is the extent of my experience of engines.
User avatar
By RichJordan
#1787134
carlmeek wrote:I’m pretty sure that’s nonsense unless the engine was mounted wonky with a cylinder pointing down!


Thanks. Will delete that bit of non-knowledge from my memory!
User avatar
By Miscellaneous
#1787137
..., there will be folks on here that have forgotten more than I know,

Moreover, unlike you, I'm keen to learn and in doing so am prepared to listen and question my understanding. Rather than to ignore explanations people offer and regurgitate the same incorrect beliefs. :wink:
User avatar
By cjrpaterson
#1787157
As someone who flies with a Rotax and is still relatively inexperienced, this topic has been very interesting and enlightening. Always good to learn more about the internal workings of these things. Perhaps we could refrain from the insults and get back to the topic? I've gurgled when the oil has been below the correct level on the dip-stick, which seems to be almost all of the time for me. It sounds like that may be due to location of the engine/oil reservoir on the specific plane (DA-20)?
Last edited by cjrpaterson on Thu Jul 30, 2020 11:10 am, edited 1 time in total.
User avatar
By Sooty25
#1787158
I do wonder if this

cmoreflyer wrote:The rotax engines are a “dry sump system”
Which means the majority of the oil is stored in a remote sump ie the oil tank.
Which is why the engine has to be gurgled or burped so you can get an accurate reading of the oil level.

Any one who thinks that by rotating the prop a dozen times will remove every last drop of oil from the engine internal surfaces into the oil tank And will cause damage to moving parts clearly has never had an engine apart..

I’ve seen engines being drained overnight tipped every which way to get all the oil out before a rebuild and as soon as you remove the cylinder head out comes a pool of oil..


was triggered by my earlier comment

Sooty25 wrote:There is of course a downside to gurgling. Turning the engine slowly to pump oil back to the dry sump tank, is also turning the engine with no oil pressure which removes some of the residual layer of oil sitting on bearing surfaces, right before cold starting.


when you also consider

Marvin wrote:Turning on the starter motor means the oil pump is putting more oil in the sump. The idea is to pull a blade though slowly, about 5 sec though a compression, so the sump pressure sends oil back though return and the oil pump is not sending oil round system. Then check oil tank level.


and

carlmeek wrote:
3. Engines that are absolute nightmares - 40 blades, still no gurgle sometimes. Could be slightly low compression perhaps?


You have to stop and wonder how much oil is actually left on the camshaft lobes at the point you hit the Starter button. After 40 blades at zero oil pressure, I'd suggest it is close to half of sod all.

If it was directed at my comment, yes I have had a few engines apart, I spent a couple of years rebuilding 6 cylinder BMW car engines for a living many years ago. You need a 15mm ring spanner to remove the cam shaft pulley off an M20 engine, if that helps.
Why were we doing so many? because of a design fault by BMW, they fitted timing belts with 128 teeth, which meant they stopped in the same place when the engine was stopped. Subsequently, the start up snatch on the belt would eventually weaken and strip teeth, resulting in a top end rebuild (if you were lucky). The cure was a 127 tooth belt and a different tensioner, so the belt stopped in a different place each time.

And the point of that is? Just because the Germans design and build something pretty damn good, it doesn't mean they've got it right!

My opinion is, pulling blades is a fudge to cover a proper solution.
User avatar
By lobstaboy
#1787160
Miscellaneous wrote:
lobstaboy wrote:
lobstaboy wrote:Why? Because a change in the oil level that is unusual is an early sign of a problem with the engine.

I'm afraid I don't see how that explanation explains why? How is gurgling going to show up an unusual change in oil level? I guess there's an outside chance a catastrophic fuel or water leak in to the engine could result in an unusual reading. But then that would become apparent before take off. From a purely oil related POV gurgling only serves to prevent overfilling


Because gurgling is the only way to get an accurate and repeatable reading. Without gurgling the level shown on the dipstick can vary, for example depending on how long it has been since the engine was last run (oil taking several days to drain etc).
All engines use oil. They are supposed to, a bit. What I'm talking about is a sudden change in oil consumption - indicating the onset of a problem.
Careful monitoring over time of the oil consumption is a simple diagnostic of the health of the engine. So is the colour of the oil.
Gurgling as recommended at the start of each flying day and checking the level and colour of the oil is straightforward.

Incidentally you don't need to be concerned about scraping the oil off the cylinder bores as long as you are going to fly the aeroplane. Are you confusing that with advice to not turn over the engine by hand during a lay off period? (The latter is, imho, good advice)

The honing marks on the bore are there to trap sufficient oil for lubrication and it stays there for a long time - the oil control ring scrapes excess oil from the high spots, leaving the oil in the honing marks. A few turns by hand are not going to remove the oil sitting in the honing marks, so the lubrication during start up will be fine.

Edit to add: Sooty makes the point about oil on bearings and camshaft in addition. Bearings should be fine - they trap oil, but maybe the camshaft is a concern. I'd certainly be concerned if I didn't get a gurgle after 20 or so blades - either poor technique or a problem that needs investigation
PeteM, Nick liked this
User avatar
By Miscellaneous
#1787169
lobstaboy wrote:Without gurgling the level shown on the dipstick can vary, for example depending on how long it has been since the engine was last run (oil taking several days to drain etc).

Agreed, however as long as there is sufficient shown on the dipstick for the flight there is no need to gurgle another couple of hundred ml in to the tank, because that is all you are doing. You have already determined you are not topping it up. Just leave it in the engine. :D
lobstaboy wrote:What I'm talking about is a sudden change in oil consumption - indicating the onset of a problem.
Careful monitoring over time of the oil consumption is a simple diagnostic of the health of the engine. So is the colour of the oil.

Again agreed, however careful monitoring of the oil over time does not necessitate gurgling every day. EG I last flew on Friday, all was well with the oil pressure, level and there were no signs of leaks. If I was to fly today I would check the oil level and if I was off for a bimble and verified the oil in the tank at half way between min and max I would not gurgle. I ask yet again, what benefit would gurgling in this scenario give? On the other hand if I was heading south for a beer with your good self and found the oil level in the tank to be just above minimum I would gurgle before topping up, thus ensuring I did not overfill. That would be the purpose of gurgling.
lobstaboy wrote:Gurgling as recommended at the start of each flying day and checking the level and colour of the oil is straightforward.

Gurgling is and should be straightforward, however it is not necessary everyday. Consider the OP, did the engine need oil? Did the pilot follow routine and needlessly gurgle resulting in the incident? What we do know for fact is that if he hadn't gurgled the incident would not have happened. Next person to gurgle is not likely to have left a 'mag' on. It's all very well folks saying they have x hundred hours and still have all their fingers, but that ain't much consolation to someone who has an avoidable incident.
lobstaboy wrote:The honing marks on the bore are there to trap sufficient oil for lubrication and it stays there for a long time - the oil control ring scrapes excess oil from the high spots, leaving the oil in the honing marks. A few turns by hand are not going to remove the oil sitting in the honing marks, so the lubrication during start up will be fine.

I say again, the risk is not ordinarily high, however not gurgling avoids all risk of leaving the cylinders dry. Particularly after a long lay off, such as with coronavirus. How many members of must gurgle fraternity went out to their Rotax's and immediately gurgled after the engine had been sitting for 3/4/5/6… months.

It may be easier to put any talk of risk of 'scraping' oil off the cylinders aside and just consider the purpose of gurgling? Why do something that is not necessary and provides no tangible benefit?
By jrp
#1787174
Imagine a situation. Nobody has flown the aircraft for three or four days. Off comes the top cowling, out comes the dipstick and the level is above the top of the flat.

Recommended to have level at least half way up the flat after gurgling . Three quarters up if it is a hot day. Oil helps with cooling.

So what happens if one gurgles the engine now? The level can only go up, down or stay the same.

If it goes up it was already above recommended so why gurgle at all?
If it stays the same, why?
If it goes down where has the oil gone?
User avatar
By Miscellaneous
#1787175
RichJordan wrote:Apologies if it's already been mentioned in the thread and I've missed it.

Is there another reason to gurgle the 912, that if left for long enough, enough oil could leak into the cylinders to hydrolock, causing damage if it's turned on the starter?

Fairly sure I've been told this by more than one person, so I've believed it, but having read the thread I'm not sure....

I have had an email from a reputable source :D advising that this can in fact be an issue with installations where the tank is higher than the engine, permitting the oil to drain in to the engine over time. I'm advised it has 'cost people thousands'.
RichJordan liked this
By Bill McCarthy
#1787179
I knew @cmoreflyer was in trouble when he launched in at page 5 with the opening statement that the Rotax is a “dry sump system”. As if we didn’t know, at the very least, by that stage.
Miscellaneous, Sooty25 liked this
User avatar
By The Admin Team
#1787184
cjrpaterson wrote:Perhaps we could refrain from the insults and get back to the topic?

Yes, please.

We should all be able to disagree without insulting one another.

I have amended and deleted some posts - please don't cause the Mods further work. Thank you.
Miscellaneous liked this
By oldbiggincfi
#1787228
What's the matter with the manufacturer's handbook ?

Are we not capable of reading and following the instruction ?

If not , then ( as suggested before) ) book a LAA Rotax course with Kevin Dilks and pay attention .

He is extremely knowledgeable and I believe, spent some time working in the factory.

Everything is stripped down to bare bones showing all working parts .

His wife is great at looking after you in the eating department .

The heading says "Rotax gurgling safety" which I understand means, what you do to keep safe .
By PeteM
#1787254
I cannot resist adding some comment. Having tried to 'hand swing' a Rotax - because we saw something on an internet forum, that it might be possible, we failed. The comment that 200rpm equivalent is necessary seemed to be pretty accurate to us.

How that is in any way comparable to gurgling baffles me. You are pulling the engine over compressions at a very slow rate. My engine, even after several weeks would gurgle after about 6 to 8 blades.

Gurgling is a slow speed operation - it cannot cause ignition. However depending upon the location of the supply tank failing to gurgle can certainly get you very close to hydraulically locking the engine and serious damage - hence the slow and careful part of the activity.

(Yes once I did once experience a hydraulically locked aero engine - Gypsy with a blocked inlet manifold drain which the gentleman could not get to start......)
By andytk58
#1787259
lobstaboy wrote:

Edit to add: Sooty makes the point about oil on bearings and camshaft in addition. Bearings should be fine - they trap oil, but maybe the camshaft is a concern. I'd certainly be concerned if I didn't get a gurgle after 20 or so blades - either poor technique or a problem that needs investigation
[/quote][/quote]

The camshaft in a 912 sits in the bottom of the engine, so unlike an O-200 where its at the top.

ie, its unlikely the camshaft will be scraped dry by hand turning the engine as its drowned in oil, no?

Andy
  • 1
  • 4
  • 5
  • 6
  • 7
  • 8