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Jaba-who

Camit engines - anyone got one?

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Anyone flying a jab wihout full cht and egt doesnt know whats going on in the engine and overheating a cylinder would be easy and damage serious.

 

 

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Anyone flying a jab wihout full cht and egt doesnt know whats going on in the engine and overheating a cylinder would be easy and damage serious.

Your opinion ! How much variation in temps on cylinder heads and exhaust occur ? Which is the hottest pot ? I do not have individual sensors and always runs cool because I don't give it a reason to run hot, cruise climb, level off every 500ft to cool, climb out never below 80knts usual 90knts ! I have observed many that ignor engine management and agree that carefully monitoring and operating is important but individual cylinder monitoring is good but no way essential ! Good engine management and maintenance is the key to long engine life. Knowing my aircraft I would happily fly with no cht or egt and don't think that is being too reckless.

 

 

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Camel, I'll bet your engine loves you and hopefully it understands just how lucky it is, but I'm absolutely with JJ on this one. There's decent evidence that chts can vary by 10C or even more (take you pick of how much of that is a result of minor variations in cooling airflow and how much uncalibrated CHT probes). Once you have actually established the cooling temp profile under use, then you will (as an obviously mechanically empathic person) know what's likely to be happening in the engine from one sensor BUT you need to be the sort of person who runs an 'engine performance' channel in your thought process (some people just do that, many don't).

 

The problem for most people in trying to do the best engine management they can, is the range of variables they need to reconcile all the time. For instance, we know that at different engine intake airflow rates, the mixture can vary considerably between pots - a full set of EGTs will show that up. I've seen the results of the Jab. installation on a motor-falke motor-glider and the nearly 18 months of testing, adjusting, testing again etc. just the intake tract airflow to try to get even temps at the 'normal' rev range, and even as little as 50 rpm. change on climb could make an appreciable difference to the distribution of temps between pots. Does it matter? - hell, yes; if you for instance get a 'bad' batch of fuel and happen to hit a particular intake velocity situation (basically, revs and load on the engine) that tends to send one or two pots high but not the pot with the cht/egt, you might never know that one or some pots are being hammered.

 

When idling in a crosswind, it's possible to get cooling airflow reversal from one side of the engine to the other, so one side can be doing just nicely, thank you, while the other is rapidly cooking. It doesn't take many minutes for that to become critical for damage. A full set of chts will alert you to that problem.

 

Finally, we also know from information supplied by Jab. engine users that seemingly insignificant changes to the under-cowl arrangements can make quite a lot of difference to cooling airflow, so if you change anything around (such as an oil-cooler hose routing, for instance) your previous experience of the engine may not provide you with the necessary information as to how it is faring after the change. A full set of chts will give you that information.

 

Finally, by having only a single cht and egt, you are relying on your previous experience that future situations will conform to the 'known' because you are applying the engine management techniques that have served you faithfully. That, of course, flies in the face (little aeronautical joke there..) of the Harvard Law:

 

Under controlled conditions of light, temperature, humidity and nutrition, the organism will do as it damn well pleases.

 

OK, I'm being a little bit facetious here. We know that some Jab engine owners consistently get excellent lives from their engines and others conversely get repetitively poor lives. Good management technique simply HAS to be a factor, it's not just a lucky-dip (though it has also to be recognised that some Jab engines just aren't up to scratch). I am rebuilding a very old Jab that has had hard use all its life, and the log-books show it has had a bad history of engine life - but I can say that other evidence from the airframe shows incontrovertibly that it has been subject to bodgey maintenance and extreme hard use. If you did not access the engine records and just looked at the airframe evidence, you'd expect the engine story to be less than wonderful..

 

 

 

A full set of cht and egt's will report the condition under operation for every pot. A fairly low-cost installation of full monitoring, out-of-limit warning and flight recording (we're looking at the MGL Extreme EMS for this) is less than the cost of a top overhaul and could easily save you that cost at 400 hours for an 'abused' engine vs. 1000 hours for a 'managed' engine. Plus which, it could save you having to recover your downed aircraft from the middle of buggery...

 

 

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Temps across the engine change significantly as rpm changes, hottest cht and egt change with engine rpm and MAP.

 

Mine sees egt on 5 and sometime 6 go over 720 at WOT..... Exactly what it shouldnt do, all the others cool.

 

Upon reducing power and descent 4,5 and 6 go up to 750 if left alone, thats serious damage ranges., bit of carb heat fixes beautifully.

 

At cruise everything is good, egt tend to be too cold across the engine but still 100 deg different. Before i fitted baffles and customised it there was 50 deg difference in CHT, hottest being number 2, going well up to red in certain situations. Others were ok to too cold, back cylinders were the coldest...... Where the std cht probe is mounted.

 

No way you cold manage this or even know the trends without the EMS and full probes.

 

Best feature of engine monitor is to pick up early a problem in flight. Leaking valve, lean cylinder even detonation and other issues are easily picked up. Many also log results helping chase trends if or when theres an problem.

 

 

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Sorry camel but you are very very mistaken.

 

We have done a large amount of work on multiple engines here in North Queensland and developed a few modifications to help in narrowing the ranges of temps.

 

Some absolute facts we have found in our research.

 

The cylinder head temps can have significant ranges of temps. (Over 60 degrees C ) in some engines from hottest to coldest.

 

The temp ranges change with different RPM settings and cylinders can swap which is hottest. Jabiru say to put that single CHT on Cylinder 6 because it runs hottest. Well that's not true in nearly half the engines. Number 2 runs hottest in many engines.

 

Its common for the temps to run hotter on one side of the engine than the other ( not always the side with cylinder 6 or 2 either) and when combined with front to back changes its common for temps to get sequentially hotter with temp rising from cylinder 1 to 6 sort of "diagonally" across the engine. But often 2 is anomalously hot.

 

All this can be changed by simple things like the carby tilting to one side (either accidentally or by being turned on purpose ) or complex things like baffles in the carby intake or changes in the jet size which change the droplet size and thus change the inertia of the fuel air mixture. (Big droplets get carried forward to front cylinders leaner air to the back).

 

You have absolutely no idea what's happening without all cylinders being monitored.

 

 

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Sorry camel but you are very very mistaken.We have done a large amount of work on multiple engines here in North Queensland and developed a few modifications to help in narrowing the ranges of temps.

 

Some absolute facts we have found in our research.

 

The cylinder head temps can have significant ranges of temps. (Over 60 degrees C ) in some engines from hottest to coldest.

 

The temp ranges change with different RPM settings and cylinders can swap which is hottest. Jabiru say to put that single CHT on Cylinder 6 because it runs hottest. Well that's not true in nearly half the engines. Number 2 runs hottest in many engines.

 

Its common for the temps to run hotter on one side of the engine than the other ( not always the side with cylinder 6 or 2 either) and when combined with front to back changes its common for temps to get sequentially hotter with temp rising from cylinder 1 to 6 sort of "diagonally" across the engine. But often 2 is anomalously hot.

 

All this can be changed by simple things like the carby tilting to one side (either accidentally or by being turned on purpose ) or complex things like baffles in the carby intake or changes in the jet size which change the droplet size and thus change the inertia of the fuel air mixture. (Big droplets get carried forward to front cylinders leaner air to the back).

 

You have absolutely no idea what's happening without all cylinders being monitored.

Mistaken about what ? Having and Watching all the gauges ? Whether it is a Jabiru, lycoming , continental or Camit and is air cooled you are going to have something to worry about if you want to sit and watch instrument instead of flying in a manner that does not cause overheating. Fly the plane right and you will have less to worry about. Also when I descend I use as much power as I can to keep engine warm. You guys definitely are good at watching the numbers, are you flying the plane right ?

 

The Camit engine has made changes, I believe the heads are a better material to withstand heat and bigger bases on barrells so they don't break away. Have they made changes to run cooler or be stronger because all engines will break if not run in a way to receive sufficient cooling, I fly with the intention to keep my engine at the right temp ! What do you do, fly watching your gauges ?. So what do you do when you see a hot pot ? Did you know shock cooling is the big killer for any engine ? What exactly does watching all the gauges achieve and how do you remedy it ? Like I said it should not have reason to be hot or do you want to trash it and push it to the limit ?

 

Now tell me exactly what you do when you see all this information on your multiple EGTs and CHTs ? Do you have mixture adjustment ? Do you have cowl flaps ? Do you have something other than the plane in flight ? Why did you let it get hot in the first place ?

 

 

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Interesting article for CHT. http://www.challengers101.com/CHT_Sensor.html. http://mooneyspace.com/topic/5633-pirep-newer-jpi-cht-piggyback-sensor/.

 

Or this, http://www.scootercentral.net/forums/viewtopic.php?f=14&t=17729

 

How do you know your getting the right information ? If you fly right, you should be fine with just routine T & P checks !

 

Multiple CHT and EGT are good but are they accurate ?

 

I would be more interested in knowing temp of oil. Why not monitor oil temp at different points too ?

 

Camit engine has an inhibiting system too ! Camit are thinking right and they are on a winner I believe !

 

 

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Mmmmmm.

 

Camel, My answer was in response to your statement

 

" I do not have individual sensors and always runs cool because I don't give it a reason to run hot, cruise climb, level off every 500ft to cool, climb out never below 80knts usual 90knts ! "

 

My response was specifically to point out to you that it is not valid to make that statement.

 

Multiple people have posted statements on this forum (and other forums) that attest to wide temperature ranges and inconsistent "hottest" or " coolest" cylinders. These findings occur in a range of conditions and flight techniques including techniques similar to yours.

 

The fact is: that to make assumptions about all cylinder temperatures at all times from a single temp probe is invalid.

 

Everything else you raise is a red herring and does nothing to negate this fact.

 

 

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Camel, as with quite a lot of debates, there is much truth on both sides! Your point that good basic flying practices that manage temps (and shock cooling too, completely agree) is essential to get a decent life from any engine - it's useless to know what's going on if one doesn't ACT on that information. And the manufacturer's recommendations aren' ALWAYS correct: Steve Wittman used to rev his small Continentals way over the recommended and pretty much always got good life out of them. However: he had a wealth of experience on which to draw.

 

The Jab cooling thread: http://www.recreationalflying.com/threads/jabiru-engine-cooling.112581/ is very instructive about just how 'finicky' and non-intuitive the whole cooling thing can be, it's worth reading. The obvious point about that is that without the information feed, one doesn't really know what is going on; I doubt that most people need to fly with their eyes glued to the gauges once they have the 'profile' of what happens established - but you can't get that established if you don't have the basic information. Jabiru themselves say clearly that one shouldn't make modifications without a full set of gauges, and you can bet that came from experience as they developed engines and cooling mods.

 

The thicker barrel bases on the CAMit barrels are a bit more subtle in effect than just 'not breaking off': what happens with the thinner bases is they bend under extreme load (especially detonation) and act as levers to magnify the force on the through bolts. If you look at used cases, you will frequently see indentations from the outer edges of the barrel flange imprinted in the cases from this effect, and it's that extra load that overstresses the through bolts. CAMit have taken a belt-and-braces approach to the whole through-bolt problem: increasing the size of the through-bolts, changing the nut base profile so full torque is applied to the barrels without introducing bending in the through-bolt shank at the nut AND eliminating the base bending problem (maybe that's belt-and-braces-and a spare belt as well!). Being CAMit, they've actually gone even further: by a complete re-design of the through bolts and the removal of the case dowels plus a new case joining technique, they've addressed two causes of case fretting - thus getting what one might consider to be 'triple-duty' of good effect from what at first blush appears to be an answer to just one problem: the through-bolt strength issue. It's that sort of thoroughness of approach that, when one has it all explained, gives one great confidence in the potential of the CAMit mods.

 

 

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Stop it, stop it.....this teasing is driving me crazy, like placing a bowl of ice cream in front of a 5 yr old, and telling them not to eat it.

 

 

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Then you'd better not go to Natfly (or send a mate there) and ask Ian Bent about the engines directly, because there's stuff I haven't mentioned that he's been working on that will be chocolate sauce and M&M's on top of the ice-cream...

 

And especially don't take a camera /send a mate with one to take piccies of anything Ian Bent might put on display...

 

 

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OK, who can we commission to do this photo talk and report task @ Natfly for those who cant attend?

 

 

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Ross (maj ) right up his alley. He,s got good background/history re jabs. And I,m serious,Ross ol son, just call it as you see it.

 

Wrong. He has no background/history with Jabiru. Just ask him. I haven't spoken to him since yesterday, so doubt anything has changed overnight. He will talk/argue ROTAX with anyone until the cows come home but will also admit his experience with Jabiru is hearsay and what he has read here.

 

 

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Thought his background was aero maintenance over many types, " hearsay" coming from pros and cons, along with " how the engines should be built" by guys that have "modded" their installs, and then proven success, all of this and more, as background, was in my view a good "base" to engage Ross.

 

Sorry Ross, I,ll get back under me rock.....

 

 

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I would seriously suggest that the best sort of person to talk to Ian and 'report' back is someone who has worked on Jab. engines and has a decent amount of experience with them. The reason for this is, if one has the necessary level of technical knowledge and some detailed knowledge of Jab. engine-specific problems, Ian Bent can talk through the causal chain he has discovered for the problem and the measures he has adopted to address those - and in many cases, it's not just a seemingly simple cause but a 'set' of circumstances that need to be understood.

 

For instance, with the through-bolt issue, we've seen in various threads (no pun intended here!) people have talked about the size of the bolts, the type of thread (rolled or cut), the nuts, the material etc., some with high levels of conviction that they have found the 'smoking gun' and an apparently simple change would resolve the problem/s. Ian Bent can discuss every aspect of through-bolt performance (or failure) and explain all of the factors and why each one is important - right down to the actual disposition of thickness at varying places along the length of the bolt. It all makes sense to someone who has seen first-hand the types of failure that occur, because the 'simple' and seemingly apparent answer is not necessarily the correct one.

 

 

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all this talk of sensors, CHT's EGT's etc etc, i try not to fly with anything less than full EGT and CHT monitors, My 912ULS is currently being modded to have all sensors installed.

 

Its nice having all the data from EGTS and CHTS, but, the BIG question, is how to interpret what its telling you!

 

assuming you are in cruise and have been for say, an hour or more..

 

1..so, your flying along, all temps normal, EGTs are all equal, and CHT;s the same, then suddenly, EGT starts rising on 1 cylinder, and the CHT is falling.. whats happened?

 

2 flying along, both EGT and CHT start falling on 1 cylinder at the same time, quite rapidly.. whats happened?

 

3 EGT falls to zero in 1 cylinder, everything else is normal...including CHT.

 

4 EGT is significantly lower on 1 cylinder, all others are normal, as is CHT for that cylinder..

 

5 alls well,, engine stumbles very slightly for a second, then, CHT starts rising rapidly. EGT is normal, all other indicators are normal.. what will you do?

 

6 EGT slowly rising in 1 cylinder, everything else is normal, CHT for that cyl is normal.

 

7 ALL EGT's rise at the same rate without any changes, CHT;s the same on all cylinders.

 

some of the 7 are minor, others can become a fatal situation rapidly if no action is taken with regards to the data..

 

and this kind of data is of very limited use if you only have 1 EGT/CHT..

 

Answers this time tomorrow..

 

 

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Good question

 

First simple point is without the info you are ballast, and in four cases you will land none the wiser and take off for another trip

 

More confusing is when the egt etc are NOT even in normal operation. Record what "normal"is. I have a few photos on the phone just in case im unsure of the spread.

 

I dont know the answers but first is fly the plane and prepare for things to get worse

 

 

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Are you flying a test bed or an aeroplane? Seriously, IF you have to do this you might consider employing a flight engineer. The DC6 had full ignition analysis in flight as on long trips a fault could produce a failure if the engine was not shut down early. Our aircraft shouldn't require this degree of monitoring in flight.

 

Another effect is the possibility of indicator failure. Is the engine or the INDICATION the problem? On most 582's it is fairly rare to have both EGT gauges working at any point in time.

 

If your engine develops vibration or rough running in flight , get it on the ground ASAP... If you fly over what you can land on it will be better for you. Mechanical failures usually happen unannounced , and NO FUEL is probably the most common cause of the engine going quiet, if normal servicing is done on the engine...Nev

 

 

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Guest Andys@coffs
Your opinion ! How much variation in temps on cylinder heads and exhaust occur ? Which is the hottest pot ? I do not have individual sensors and always runs cool because I don't give it a reason to run hot, cruise climb, level off every 500ft to cool, climb out never below 80knts usual 90knts ! I have observed many that ignor engine management and agree that carefully monitoring and operating is important but individual cylinder monitoring is good but no way essential ! Good engine management and maintenance is the key to long engine life. Knowing my aircraft I would happily fly with no cht or egt and don't think that is being too reckless.

Camel

 

I don't agree with you at all. As a result of the rebuild required on my J3300 I put EGT and CHT on every cylinder. Conventional wisdom has it that the rear most cylinders are the hottest. On mine looking from the front to the rear of the aircraft the front RH side cylinder and the middle LH cylinder are the hottest. Std from J I had 2 EGT and 2 CHT gauges fitted to the rearmost cylinders and of course they showed all was fine.....

 

In fact they are significantly hotter than the others and hotter than I would like and as such I'm off to Cessnock shortly to have the Maestro put his pressure gauges on the system to work out why it isn't cooling better than it should.

 

The reason for the overhaul before was due poor leak downs. The cylinders and pistons were all out of round due heat. Because I do the maintenance called for, and believe in the go/no-go rules around leak downs it didn't fail in the air, but had I pushed on or stretched I may very well have transitioned to glider pilot......

 

Its my opinion that the J engine as it is, is not fit for purpose. Anything that can be used to identify problems and have them dealt with is worth having. The cost of the EGT/CHT system is not cheap at all, the cost of a full overhaul however makes it look like chicken feed!

 

So, it maybe that your approach will work for you, but I think I'm careful with what I do and I still needed to find a lazy $10k to have it put right (well restored is more accurate than right!)

 

Hopefully the camit fixes will address the deficiencies that in my opinion are clearly present in the current engines.

 

Andy

 

 

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Andy - if more people would actually go through the exercise you are going to do with (I assume) Keith Rule, I am personally quite sure that there'd be a far better body of information out there for all Jab. owners. Perhaps, when you have the results, you can share them - maybe on the 'Jab Cooling' thread?

 

The whole question of whether Jab. engines are 'fit for purpose' or not, is absolutely open to debate. Jabiru, of course, maintain that they are - if operated within the prescribed limits. I think it is a fair proposition that Jabiru is prima facie correct in that assertion; they have testing that demonstrates compliance within the standards required. However I think it is equally a fair proposition that the prescribed limits are damn difficult to adhere to and it is frankly too fine a tolerance for 'reasonable' operation. If we are to assume that most owners do NOT willfully operate outside limits and make their best efforts to fly conservatively, (people who continue to use their engine with one pot without compression when cold excepted..), entirely too many owners are experiencing problems they simply should not be having. I would agree with you that there are deficiencies in the current Jab. engines that are unacceptable for operation in real life, where factors that are outside the control of the operator (such as variations in fuel quality) mean that damage occurs through what should be expected minor transgressions of the 'prescribed limits'.

 

Ask any aero-engineer involved with engine performance testing and you will be told that cooling airflow performance for air-cooled engines is one of the most difficult areas for design and certification. It looks simple: stuff enough air past the barrels and heads, and it should be ok. It just doesn't work like that, and worse: what may look efficient, may in fact not be. It's arcane science at its best: you need velocity, distribution, lack of stagnation points, heat transfer rates etc. all to align.

 

From what I have seen of the CAMit mods, they will build in a very considerable improvement in tolerance to operation a bit out of limits to the standard Jabiru engine and they will resolve a number of other problems not directly related to cooling performance. However, it would be ridiculous to suggest that any mods to the engine can negate a fundamental fault in the cooling airflow, so the exercise you are currently undertaking is of great value.

 

I guess that I'm expressing an article of personal faith here, but my co-owner and I have put our money on the line that the combination of the CAMit mods plus attention to the whole cooling airflow situation - to be developed through testing - will give us an engine we are happy to fly behind and will more than repay the upgrade costs for the engine. We have a lot of airframe work to do before our wee beastie gets back into the air, but I will be posting our findings. If you can help with providing information about your cooling airflow tests, I believe we can all contribute useful information, out of which hopefully will come a 'profile' for Jab. / CAMit modded Jab. engines to deliver the sort of performance all owners hope to get.

 

 

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Heat,heat,heat........it seems to be "the key to longevity etc "

 

Ok.......why don,t we just plonk on water cooled heads, ie Rotec ones, seems relatively easy to do, .....prob solved ??

 

 

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It certainly sounds attractive, but in practice I believe you need to design the engine from the start for one type of cooling or the other. A hybrid - and obviously a Rotax is a hybrid - needs to have both efficient barrel cooling AND efficient head cooling in the form of a radiator (or heat exchanger), plus oil cooling, all integrated into the design. So the cooling airflow requirements for all three components need to be considered; and if there is a water-cooled element in the equation, a form of pump to circulate the water. There will be a weight and cooling drag penalty for the additional water-cooling element, plus an additional mechanical complication element: hoses, pump, heat exchanger. To do the job properly, you'll need to substantially revise the 'old' cooling airflow arrangement to both provide decent barrel cooling and a sensible airflow past the heat exchanger - while not affecting the oil cooler operation..

 

If you add weight to the engine and the FWF installation at the front of a Jab., you may well need to add more ballast at the tail to keep the c/g range the same, so it's not just the added weight of the engine and heat exchanger that counts. That MAY affect the stall speed, so proper performance testing to ensure the POH is correct MAY be needed.

 

All do-able, at a cost. Not an option for non-certificated LSA aircraft I believe ( i.e. for Jabs. that are not 'C'-registered 24-aircraft); may require an Experimental certificate and the requisite hours of flight for unrestricted operation.

 

All of which is not to say that it isn't a viable option. However, if there is a simpler way to go that is comparable in results and better in cost and the CASA etc. embuggerance factor, which to choose? What we need here is for someone to actually do the LCH conversion and report back on the details and cost of the project.

 

 

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Are you flying a test bed or an aeroplane? Seriously, IF you have to do this you might consider employing a flight engineer

Actually, checking your engine monitor is no more time consuming than a usual temp and pressure check that should be done every 10 - 15 mins or so.. just a quick glance is all thats needed.

 

and the information that can be gleaned from such an instrument can save $$thousands in maintenance trouble shooting issues, and can save your life or aircraft by identifying serious issues well before they happen, and could possibly identify issues with Jabiru engines that are causing numerous failures.

 

as for what info you can get from the scenarios earlier..

 

1.

 

so, your flying along, all temps normal, EGTs are all equal, and CHT;s the same, then suddenly, EGT starts rising on 1 cylinder, and the CHT is falling.. whats happened?

Exhaust valve leaking..

 

2

 

flying along, both EGT and CHT start falling on 1 cylinder at the same time, quite rapidly.

Injector clogging or an induction leak allowing mixture to lean out to cutoff. (such as a gasket leak.

 

3

 

EGT falls to zero in 1 cylinder, everything else is normal...including CHT

EGT probe failure.

 

4

 

EGT is significantly lower on 1 cylinder, all others are normal, as is CHT for that cylinder..

Exhaust system leak.... could be a serious issue, (especially if its in a cabin heat muff) watch that CO monitor until you land, and land ASAP.

 

5

 

Alls well,, engine stumbles very slightly for a second, then, CHT starts rising rapidly. EGT is normal, all other indicators are normal.. what will you do?

indication of Pre-ignition... the fastest way to destroy your engine, and it could happen within seconds or minutes. ,could lead rapidly to seriously overheated cylinder/s best get mixture to full rich, or power back below about 60% to stop preignition. Land ASAP. (usually caused by cracked plug ceramics creating pre-ignition hotspots)

 

6

 

EGT slowly rising in 1 cylinder, everything else is normal, CHT for that cyl is normal.

Dead spark plug (1 of the 2 per cylinder) or plug gap out of limits causing poor or no spark, might explain hard starting in the mornings. if you know which mag runs which plug, a mag check will identify the failed plug. (mag check of the dead plug will give a very significantly lower EGT during the mag check compared to the good plug)

 

7

 

ALL EGT's rise at the same rate without any changes, CHT;s the same on all cylinders.

Failed Ignition system. now operating on one "mag" this will also bee seen at every mag check during runup, or top of descent mag checks, a great way to ensure every plug is working fine during your runup. or identify a bad or fouled plug, or lead.

 

Sadly proper engine management skills are lacking in the training syllabus, but with the info gleaned from such instrumentation, im sure a lot of failures could have been prevented before they happen. not only save a heap of time, as a failed plug etc could be identified and rectified before the next flight, or save heaps in your L2 having to troubleshoot everything to find the issue.

 

without a CHT or EGT on every cylinder, how can you tell if one has been running well over temp every time you fly? or one has been suffering from severe detonation for most of the time?

 

(detonation usually gives a slowly rising CHT with no change in EGT)

 

im sure quite a few Jab failures are the results of these conditions that have gone undetected leading to eventual premature engine failure.

 

 

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