I need some help with my favorite engine, the Enya 53-4c. The engine is about a year old with one and half gallons of fuel thru it. Last month I lost my muffler half inflight. I did not touch any settings before or after I lost the muffler half. Yesterday I installed a new OEM Enya muffler and ran her up on the stand and she was knocking at wide open throttle. I richened it up 500 RPM from max RPM and it was running fine on the club set-up stand but when I throttled up for T/O she was knocking at full throttle. I put here back on the stand richened it up 1000 RPM and it ran rich but fine. Throttle up for take off and it knocked the prop loose on the shaft. Here is my set-up: She is mounted right now on a Spacewalker II inverted with a APC 12-6 prop, Enya #3 plug with Omega caster/synthitic 5%. I was reading my Enya paperwork last night and it recommends 5-10% caster/syn blend and also recomends using a head gasket if the engine knocks with a 12-13 inch prop. Has anyone experienced this ? And what was the fix? Prop down to a 11-6?

Dr. Bellows,


This is strange.

In the first part of your description you wrote about richening from maximum RPM...

As you lean the mixture in a four-stroke engine, running at full throttle, it gradually speeds up, eventually reaching maximum RPM.
As you lean it a bit further, it will start knocking softly and lose RPM. A bit more leaning and it will knock hard, backfire and throw the prop.

If leaning the mixture causes the engine to speed up, it is not the dreaded 'knocking' that you hear.
Knocking only happens if maximum combustion pressure is achieved, as the piston is still rising toward TDC and this will act to slow the piston down and reduce the RPM, even before the knocking becomes hard enough to stop the engine dead.

As I wrote in another thread, the main function of the fuel needles in a glow engine, is to control the ignition advance, since a lean mixture will flash earlier and burn faster than a richer mixture.


Could your engine have a loose valve (too much valve clearance), or could your con-rod have developed excessive looseness at either end? Are the piston bosses not 'egged out'?

I would think your Enya would turn that APC 12x6 no problem in the 10000 RPM range. Are you using a tach. for tuning? Too large of a dia. prop. will produce a knock. Personally, I have never been to keen on Enya plugs. I would first try a OS F plug, check the valve train and take it from there, then try a smaller prop.

One of my OS 120's developed a knock last year that was different from an ignition knock. Turned out to be a bad rear main and one cam bearing was iffy. I concluded it was most likely a bearing problem because the RPM had dropped considerable and it seemed to be running a little warmer.

Here is more info: Upon partial teardown I noticed very weak compression and a lot of blow-by from the crankcase nipple. I dissasembled the engine head and found no bent pushrods or sticking valves, sleeve looks excellent. I pulled out the front housing found the connecting rod in good shape. The timing box was removed and found no striped gears. Hope this helps for you troubleshooters.

I have compression now. When I cleaned up the the head and rockers she feels normal. Hopefully the weather will hold up later this week for a test flight.
DB

This is incorrect. A lean mixture will not flash any sooner than a correct mix.

The richness of the fuel charge does nothing for the ignition timing....the start
of the burn. A greater amount of fuel takes longer to burn, (richening the mixture)
which allows it to get over the hump....into the ATDC where the force can be
applied to the downward motion of the piston. A normal burn, with too much
compression causes the cylinder pressure to reach maximun before the piston
reaches TDC, which causes the detonation....or "ping"....because the burn was
started too early.

This is the same as having too much spark advance in a spark plug engine. It
has nothing to do with the carb mixture, asuming that the mixture is near normal.

Keep in mind these engines are like a compression ignition type, similar to a diesel.
We do of course have the glow (or spark) on all the time. When the compression
and heat of the air/fuel charge builds up to the point of explosion, it does just that...
set off by the glow plug.

The correct way to retard the timing is to lower the compression, or....to a lesser
degree....use a colder plug. Keep in mind also that the heat range of a glow plug in
completely different from a spark plug.

If this statement were true, there would be no such thing as detonation....richening
the mixture would be the cure-all. Trust me....this is not the case. Richening the
mixture can mask the detonation some what, but it does not alter the actual timing
(firing) of the fuel charge.

FBD.

Dave,


You often choose to argue with what I say, often when I am right and I usually am.

A richer mixture is slower to ignite, since it is colder than a leaner mixture, so ignition does take place later in the cycle, when the piston is closer to TDC.

As the piston rises it heats the mixture by compressing it. It will need the piston to compress the cooler rich mixture further, to allow it to be ignited, than if the mixture was leaner and warmer to begin with.

And as you wrote, a richer mixture does take more time to burn.


So, from where I am looking, the richness of the mixture, the magnitude of which is achieved using the fuel needles, is the glow engine's equivalent of turning the distributor in the direction of its rotor's rotation, or in the opposite direction, in your car's engine.


And about detonation, a rich mixture can even cause detonation, due to the sheer volume of the fuel, increasing the resultant compression pressures (liquid fuel is incompressible).
Please see the current thread about "Engine throws the prop nut, starts backward...".

This may be unrelated, but I've seen it fool some very good engine people over the years.

Ensure that your battery, or other solid object, is not vibrating and creating the noise that you are hearing. Our ears and our brain can be fooled fairly easily, in this regard. Don't ask.

I would have suspected the upper end of the connecting rod also, if you flew the engine for a while after losing muffler pressure when the muffler came apart. You did say that you checked the connecting rod, so this probably isn't the culprit. Enya's are built really well, and it would surprise me if this were true. But, it's just something else on the check list.

Since you had the engine apart, I assume that you checked for carbon build-up in the cylinder and head assembly. A spec of carbon could be acting as an unwelcome ignition source.

Good luck finding your way out of this dilemma. Please let us know the cause.

As to those Enya glow plugs, there are none better in an Enya. My 14 year old .46MKII still has the original in it. And that is after three years operation using Fox 15% nitro fuel with 20% castor, several years on Byrons and finally WildCat Premium. Here it is waiting to be mounted on a US Aircore Colt 40. It will be the third USAC plane it has been on.

Dr. B, is your .53 the TN version. Also, were your timing gears rusty, I took mine down to inspect things about a year ago and the were really rusty. I now remove one of the carb bracket mounting bolts and inject Corrosion X between uses. The rust is almost gone as Corrosion X removes it over time as long as it's just surface rust.

Dar Zellon....you are completely and utterly incorrect about your detonation "theory'.

A rich mixture cannot "cause detonation" in any way shape, or form.

DETONATION :

Definition: An unwanted explosion of the air/fuel mixture in the combustion chamber
caused by excess heat and compression, advanced timing, or an overly lean mixture.
Detonation, or "knock", greatly increases the mechanical and thermal stresses on the
engine. Also referred to as "ping".

This statement is incorrect as well. The compression ratio of a glow engine is the
primary factor that determines the firing point (ignition) of the fuel charge.

The reason I brought this up, is I don't want inexperienced Members taking
misinformation from these RCU boards.

Flyboy Dave. [8D]

In this case you're completely wrong Dar. For assumptions sake, let's say the Enya can run for 10 minutes at full throttle on 150cc (about 5 ounces) of fuel at 10,000rpm. In that time the engine has turned 100,000 times or 50,000 power strokes. This means that each power stroke needs 0.003cc of fuel (which contains about 0.0006cc of oil).

The Enya in question is 8.7cc so it'll have a combustion chamber volume of approximately 1cc to give a C/R of 9.7:1. Now let's run that engine terribly rich by doubling the amount of fuel that goes in per power stroke to 0.006cc of fuel and let's assume that none of that fuel vapourises into a compressible gas. The combustion chamber volume shrinks to 0.994cc and the compression rises to 9.75:1, hardly enough for detonation even if it could ignite.

In the real world the fuel component vapourises and gets compressed so it's only the miniscule volume of oil remaining that can add anything to the compression.

--------------------------------------

When I first got my Enya 80-4C, around fifteen years ago, I had very little flying experience with four-stroke engines. Lots of bench time, but not much flying time. My 80 did not come with a muffler, just a straight pipe. It wasn't really all that loud running a 13x6 prop, but I was worried what the other club members would think about it, so I did several polls at the field, asking whether it was too loud or not. Everyone said it was just perfect as it was and not to buy the later released muffler for it. I didn't.

One thing about running with the straight pipe was that you could hear each and every miss, clear as a bell. With the Enya #3 and Tower four-stroke plugs, it did miss, but it never quit and it ran quite well. But that miss was getting to me. No matter how I tuned the engine, even though it was running perfectly, I couldn't get rid of the occasional miss. I even nicknamed it "Five O'clock Charlie", from the MASH episode that featured the lone commie biplane bomber that flew by at five every afternoon, missing and sputtering all the while. My Enya didn't miss like that, just occasionally. Someone loaned me an OS Type-F plug to try. I checked for interference and discovered that, indeed, the piston was just barely touching the tip of the glow plug. No problem, I installed two washers. The miss was gone!

Now, was it the difference in glow plugs? Or the ever so slightly reduced compression when using two washers? I'll never know, because I "assumed" it was the Type F glow plug. I wish I had put two washers under the Enya #3 glow plug to find out. Enya four-strokes have quite a bit of compression, when healthy.

That was an exceptional Enya 80 4-C, or so I have been told. As I brag - er - mention from time to time, that engine would provide enough power to let my Goldberg Cub climb in knife-edge flight. Honest Injun. Since they are fairly rare engines, I've never seen another one run, so I don't know if I had one of those one of a kind freak engines that occur every once in a while or not. I'm about to find out. I just bought another Enya 80-4C from one of our RCU brethren. All I have to do now is pay for it! The check is going out tomorrow. Honest!

Brian,


Please read about the exact situation I was talking about in [link=http://www.rcuniverse.com/forum/m_3504643/tm.htm]this thread[/link].

It does not talk about a steady state, very rich running situation, as does what you wrote above.
...And I fully agree that detonation cannot happen in this situation which you described.

That thread talks about a specific situation, which occurs in certain larger glow engines, running at a very rich, low RPM setting, during which a lot of excess fuel, in liquid state, has accumulated in the crankcase.
And attempting to increase RPM, by opening the throttle, causes all this fuel to be 'rushed' into the cylinder, within a few revolutions.

It does not do this only in theory, but in actual practice.

You are welcome to comment in that thread too, but with all the props thrown in this situation, you cannot say this cannot happen, as it actually does.

Hi Chaps

There seems to be an awful lot of "experts" on this thread, just like at my club field

It is perfectly clear that Dar does actually know what he is talking about in this thread and is focused on the problem, unlike some others.

A glow engines timing, two or four stroke is a mechanically fixed period. This 'timing' is set for an optimum ignition point. This optimum ignition point will only be arrived at when all other variable factors are correct i.e. compression, fuel, air and heat. Should any one or all of those factors change then the IGNITION timing will change. Compression will also affect the timing, but although this is fairly well set by the design of the engine, this too can be changed by the fuel.

Too much heat and the engine will run lean, because it will use all the available fuel before it should, leading to advanced ignition. Too much fuel and it won't use all the available fuel because it won't be able to burn it all, it will therefore run rich and have retarded ignition. Too little fuel and you have two situations, one: the engine will run lean (advanced ignition) and/or two: the engine will develop too much heat (advancing the ignition)

Therefore QUOTE "the main function of the fuel needles in a glow engine, is to control the ignition advance" UNQUOTE
or/and, as not stated - ignition retardation.

So Dar's statement, if put into context is TRUE.

The only variable in a glow engine is the fuel! So unless you KNOW different, lets hear it[8D]

I'm sure Dar will be graceful about your apologies

Regards

Steve

Steve,


Thank you for what you had written.

It will not be necessary for Brian to apologize.
He and I often have our differences of thought and openly discuss them in the forum.

There are no hard feelings on my part, when someone disagrees with what I write, nor do I think, on Brian's part.

It is different, however, if someone becomes abusive, when he, or his own assumptions are disagreed with. I have seen this happen too, from time to time.

Even I have had my incorrect assumptions that made a few of my inputs, over the last 30 months, look like those of a real 'engine guy wannabe', so to speak...

But there are some misconceptions in the engine world, which most modelers take for fact.
I especially enjoy shattering these misconceptions and have done so several times.


BTW, when I wrote the needles directly control the ignition advance; what I meant is 'the amount of advance', which could also mean retardation (firing after TDC).
But I know of no engine that would actually run in such a state. Zero advance (firing at TDC), I believe, is the minimum.

Dar

No problem, the exchange of ideas and knowledge is what it's all about[8D], BUT as was mentioned in one of the posts :

>>The reason I brought this up, is I don't want inexperienced Members taking misinformation from these RCU boards.<<

[sm=wink.gif]

Steve

Dar,
That other thread talks about a flooded 2 stroke kicking back, this thread, unless I'm very much wrong, is talking about a 4 stroke which doesn't usually have a problem with fuel filling the crankcase and flooding up into the combustion chamber. My comments here were strictly limited to your statement in this thread that a rich mixture can cause detonation by raising the compression. A rich engine is an entirely different thing to a flooded engine.

If the timing is "fixed", why do you have to richen the fuel mixture when using a larger prop to eliminate preignition?

There is an interplay between all of the conditions in the engine. Just as the high speed needle affects the low speed setting and the low speed setting affects the high speed setting, on most glow engines, one can adjust when ignition occurs by varying the mixture, the load, the type of glow plug, the fuel mixture and even the amount of cooling air available to the engine. Not a terrific amount, but it does have an affect upon ignition timing.

I don't consider myself an expert, but I do consider myself to be experienced. Yes, I make mistakes sometimes. Usually I misspeak. Think one thing and type another. Other folks have been guilty of the same thing. Or perhaps they could have expressed themselves better. I know I always think of a better way of saying things once I have posted the article.

What disappoints me sometimes is that some folks are so concerned with what they perceive as their position on the social ladder, that they become terribly upset when someone disagrees with them. It reveals more about their personality than they could ever imagine.

I don't know about the rest of you, but I'm not perfect. Nor do I want to be. There was only one perfect man and look at what happened to him. <G>

Ed

It's because the engine has a mechanically 'fixed' timing that the ignition timing is varied by the fuel, which is why you may have to richen the fuel mixture when using a larger prop. A larger prop usually runs at a lower rpm so in order for the ignition to occur at the right time, the ignition has to be retarded. You could achieve the same thing by lowering the compression.

There are two important terms here, timing and ignition, one we can't adjust without mechanical intervention the other we can by using the mixture screw.

To all:

If the term "expert" upset anyone, as used in my initial posting, then I retract it, but it seemed like the right word when you consider the stance some contributers were taking. It is unfortunate that we speak as we find in my part of the world, this I concede can ruffle some feathers on occasions, but my intentions are honourable and no disrespect was meant to those of good heart.

Steve

Brian,


Agreed.

Flooding can cause detonation and kick-back, in more than one situation.

This flooding can be a result of over-priming; causing kick-back while attempting to start an engine, often resulting in a backward start.

But it can also be a result of trying to run the engine too rich, at low revs, causing fuel accumulation in the crankcase, which in turn rushes into the chamber as the throttle is advanced, which as an incompressible fluid causes the compression pressures to be excessive, which causes the same detonation and kick-back...

Both threads are related to detonation, directly, or indirectly (sound).

Did anybodyy consider that his fuel source is the cause for the engine leaning out and detonating? Could it be that he is getting a lean operation during take off. All the other arguments aside, it seems the engine is leaning out after setting the needle valves to the desired point of operation. That means either a piece of debris is in the way (causing a restriction) or the fuel source is off somewhat.

Cheers,

Chip

Someone once said...."don't confuse me with the facts, I already have my mind
made up."

First off, we are not talking about pre-ignition here. Fact; pre-ignition comes
from an alternative ignition source....other than the glow plug in our case.
Fact: the ignition timing in our compression/glow ignition engines is controlled
primarily by the compression ratio....period.

Other factors contribute and effect slightly the precise ignition of the fuel charge.
Lets keep the discussion on detonation.

Fact: Detonation can be caused by:

1. Lean fuel mixture
2. Fuel octane too low
3. Improper ignition timing
4. Lugging
5. Carbon deposits
6. Excessive milling of heads or block, which will increase compression ratio.

Lets examine these factors, and apply them to our glow engines shall we?
1. A lean mixture (not enough fuel in the air mixture) will burn out before the
engine reaches TDC and cause detonation...."engine knock". An ideal mixture
will burn in a controlled manner and apply maximum combustion pressure to
the piston just after TDC., at the end of the burn. Maximum combustion pressure
does not occur (or should not) at any time BTDC, or power will be lost....simply
because the piston is traveling in the wrong direction when the force is applied.

A rich mixture takes longer to burn. This is real simple to understand. A rich mixture
will reach maximum pressure later, or further past TDC. This will effect a slight loss
in power because the piston has traveled further down on the compression stroke.
The maximum power could have been developed if the force had been applied earlier,
at the proper time.

Fact: there is no circumstance where-in and engine will detonate due to a rich
condition. Nor will an engine detonate and backfire due to an accumulation of fuel
(resulting in a rich condition) suddenly "rushing" from the crankcase to the
combustion chamber.

A rich mixture can help overcome detonation, and mask it, and even prevent it....
but itwill not "cause detonation" in any way shape or form....that's a fact.

2. Although "octane" (gasoline) does not apply directly to our alcohol/glow engines,
the fuel in our case is still the second leading cause of detonation in our engine. A
high compression (even a European two stroke) will detonate like heck if too much
nitro is used in the fuel.

Keep in mind, my previous statements that will continue throughout....the
compression of the engine is what controls the ignition timing (advance) not the
carburetor, or the adjustments of the carb.

Fact: if you have a high compression engine (Euro) and it is designed to run on 5%
maximum....it will detonate like mad, with say....15% nitro. BTW, I just found this
out the hard way on a new .91 ASP 2-stroke.
Fact: there is no adjustment that can be made to the carb needles that will eliminate
the detonation. You can mask it, and you can extend the burn time to get it further
over the TDC point....but you cannot eliminate it without either lowering the amount
of nitro, or lowering the compression ratio by adding shims to the head.

Fact: (again) the compression determines the timing (firing) of the charge, not the
needle settings. The nitro makes it worse because the fuel burns faster, and hotter
Heat=Power.

Stay tuned....I'll finish this post later, examing the other causes of detonation.

FBD.

Dave,


How can the first small paragraph in your post, agree with the second paragraph?

The second paragraph, or rather the exact opposite of it is FACT, yet you are not willing to accept it.

The detonation that causes this type of kick-back, results not from a rich mixture, but from the sheer volume of the accumulated fuel, from the crankcase, which is suddenly transferred into the combustion chamber and causes an artificially high compression ratio.
When there is a lot of liquid fuel in the chamber, there is less room for the compressed mixture, hence the reason for detonation.


Another fact; a cool, rich mixture is less volatile than than a lean, lukewarm air+fuel mixture.
In other words, a rich mixture will ignite later than a lean mixture, which means a lean mixture will result in more ignition advance...
Isn't this exactly what you are trying to disprove??

Also; the amount of energy that an engine releases in one cycle is a function of the amount of air... Yes, if there is enough fuel, or more than enough fuel, the amount of air determines how much of this fuel will burn.
And in a mass-to-mass stoichiometric ratio, the amount of air changes very little, but the amount of fuel can be halfed, or doubled, or tripled.

If you decrease the amount of fuel to about 80% of stoichiometric, the engine will not fire (no stratified charge in our glow engines...)
But you can double, or even triple the amount of fuel.

But will you get significantly more power??? NO!
Not beyond about 1.2 stoichiometric, which we normally run and even then it is only about 5% more than 1.0 stoichiometric.


So, I would not want to burden you with facts, Dave, but why does the torque actually increase by about 30-40%, while leaning from a rich two-cycle setting, to peaked, at the same RPM? We are, after all, using the same amount of air, aren't we?

An engine will spin a much large prop at a given RPM, when leaned out, than when running rich.

Could we just be getting closer to the ideal ignition advance, by leaning the mixture? Nah, that can't be... You say.

But the fact is this is exactly what we are doing.


And as far as octane rating goes, methanol is around 120 (please correct me, Brian, if I am in error), even though it contains absolutely no octane (C8H18 hydrocarbon).

You know what, Dave, Brian?


Thinking about this more and while knowing that both facts are true; a lean mixture ignites more spontaneously than a rich mixture and also burns more quickly, it doesn't really matter...


What does matter, for maximum power, is that the timing of maximum cylinder pressure occurs just a split milli-second after the piston has surpassed TDC.

What we have to control the timing of this event, in a given spark ignition engine, with a given C/R, running at a given RPM and temperature, under a given load, is the spark advance (the mixture strength is nearly a constant, due to emission laws).

It really doesn't matter if this maximum pressure is achieved just after TDC, by utilizing 10 degrees of ignition advance, or 50.
Just that the maximum cylinder pressure comes on time, every time.

In our glow engines, with all the other 'givens' from the above paragraph and with a given glow plug and fuel (you cannot change them while the engine is running, can you?), the only control we have over the timing of this maximum pressure, is the mixture strength, which controls the propagation of the fuel burn.

So, it doesn't really matter, like with spark ignition, when the glow ignition actually occurred.
Just that the maximum cylinder pressure comes on time, every time.

If the compression of an engine is the only thing that determines the timing of an engine how does my old Saito 80 (the same model that Clarence Lee did a review on and measured the compression ration at 15:1) run at all? It also seems to love burning the high nitro fuels 15%+ too. I have also ran it quite lean with absolutely no knock (detonation, preignition). It has never once thrown a prop in the 15 years i've own it.

Fact: an engines combustion chamber shape and squish areas will play a big role in whether an engine will be prone to detonation or not. Look at the May "Fireball" head which allows a high compression engine to burn substantially leaner mixtures than the usually employed combustion chamber shapes.

I would say that an engines timing is a much more complicated affair than compression alone.