I looked into the OS web site; not the American distributor's site, but the original, English language, Japanese web site.

Please look [link=http://www.os-engines.co.jp/english/line_up/plug/pluindex.htm]here[/link] to see which OS glow-plug, OS recommends that you use in your OS engine.


This is for all that recommend running 'F' plugs in big two-strokes, or the A3 in the .91FX.
Also, to all those shops 'giving away' A3 plugs to buyers of all two-stroke engines...


The A3 is recommended ONLY for two-stroke engines smaller than .32 cid; and for LA engines up-to-.40.

The #8 is quite universal, being medium heat.

For the .61-.91FX, .65LA, 1.40, 1.60, BGX, Etc., the right glow-plug is the cold A5; not the hot A3.

And, BTW, have you ever seen any A5 glow plug offered for sale in your LHS, for use in your new, large displacement, expensive OS engine?

I sure have not...


What would you say about this, Bax?

DarZeelon.
my OS 91 FX came with an OS type #8 glowplug.
[&:]

Kostas,


...Which is OK, with the low nitro fuels that you have in Greece.

OS does not limit the #8 glow plug to smaller displacement engines, but still, if OS says the A5 is better for the .91FX, should I need a replacement, I would opt for it and not for the #8.

The A5 should cost a bit less too, compared to the #8.

I 'm glad we have many other choices in plugs. I rarely use OS due to the cost and my engines run just fine

M,good to say this.
A question is that i know that the OS #8 glowplug is hotter than the #A5,but when running the OS 91 FX,
what's the real difference between these glowplugs?
Also,in an 91 FX can i use an #A3 glowplug,if the engine is inverted???
[&:]

Kostas,


I would generally say no.

If the best specific solution is the cold A5 and the universal #8 can also be used, the A3 may be too hot and will require the mixture to be set significantly richer, so as to prevent the engine from suffering from detonation.

You would actually see that you can close the needle further, without risking a lean-run (which is actually detonation), when using the cold A5, compared to using the hot A3.

The price difference between the two is equivalent to the difference in fuel consumption for 15-20 minutes of running...

That is all.

I would not recommend using the A3, unless there is no other glow plug and you must run the engine NOW (and the fuel waste for these one-two flights that you MUST make, is reasonable).

Replace the A3 with the more suitable A5 glow-plug, ASAP!

I believe it would more accurately be described as preignition, which is not the same as detonation although preignition can often lead to detonation.

It has been my observation that a glow engine that is too lean behaves a lot like a model diesel engine that is overcompressed and a spark ignition engine that has it's ignition timing over advanced. This leads me to think that we actually use mixture adjustment to fine tune the ignition timing of glow engines. Glow plug heat ranges and head gasket thickness is used to make course adjustments in ignition timing but the mixture fine tunes it. If you take a Cox .049 engine and add several head gaskets to lower the compression, you will find that the engine wants a leaner mixture for peak power.

B.L.E.,


Pre-ignition is an ignition caused by a hot-spot within the combustion chamber, like a sharp edge on the piston, or the head, or carbon deposits. In a spark-ignition engine, it can even be the electrode of the plug.
In a glow engine it is nearly always the glow-plug coil that initiates the ignition.

So too hot a glow-plug would simply be an overly advanced ignition point. And yes, this can cause the fuel-air charge to detonate, as the piston continues to rise and compress it, after the advancing flame-front had hit it...


About the needles being the ignition timing control, I have been saying it all along, in several past threads here.

With the compression ratio being a given value, as is the fuel you filled the tank with, the prop load you are using and the glow plug you installed, the needle is the only thing that allows you to change the ignition timing.

With a leaner mixture being easier to ignite and faster to burn, it is clear what must be done to increase and optimize the ignition advance. Just screw the needle in a bit.


Using too hot a glow-plug (or too much nitro) requires you to use more fuel, to delay the ignition, reduce the advance.
This fuel is just wasted, just leaving you more gunk to clean off the plane after the flying day.

...Not to mention that you had to pay for all that fuel.

Why are their plug recommendations suddenly gospel truth but when it comes to running in engines (on the same site)they don't know what they're talking about? BTW, if you read the instruction manuals it seems that just about every engine is shipped with a #8 plug. The manuals also advise trying different heat range plugs to get the best performance. The original post is too much of a generalisation.

I was waiting for you to come in, Brian and foresaw this response.

When selecting a glow-plug heat range for an engine, it is a design decision.
Deciding how to perform the break-in, is experience based and also based on being able to change the way you think, about different engine designs.


I was also taught that break-in always requires a slobbery mixture setting.
...And I was also taught that during break-in, an engine may fail, once in a while...

I would have done it that way... But then I started thinking about what I was doing, as well as trying to figure out, who makes more sense about ABC type engines; The geezers with ringed and lapped engine experience, or George Aldrich, Clarence Lee and Harry Higley, with their informed, engineered reasoning.

I chose the later and then wrote about it.

And no, I cannot figure out why OS does not bother to differentiate, between ABC/ABN engines and ringed engines, as Super Tigre does, in regards to the break-in technique in their manuals.

My 91fx seems to run better with a OSF plug compared to a OS8.

What prop are you running,rpm range and fuel?
Can you post any pics?

Hi!
There is no glow plug recommendation that should be interpreted like it was the writing of god (or OS)!
Glowplugs are a thing that work different for different engine applications.
saying that the OS .90 FX ...or whatever should always be run on an OS 8 or Enya 3 or ...is not true. It's only a recommendation! Which means that under normal conditions running normal prop sizes, under normal temperature, using normal fuel, having normal cooling for the engine, running at normal rpm, at sea level... or what ever the manufacturer had in mind...then this or that plug will work good.
But saying it's the best plug for that engine for every application is not true!

Regards!
Jan K
Sweden

>>> Pre-ignition is an ignition caused by a hot-spot within the combustion chamber, like a sharp edge on the piston, or the head, or carbon deposits. In a spark-ignition engine, it can even be the electrode of the plug.
In a glow engine it is nearly always the glow-plug coil that initiates the ignition. >>>

Is this why it doesn't matter that all of OS's "long" plugs are actually a short reach? These so called long plugs leave lots of threads exposed inside of the head. Being used to gasoline engines, I thought this would lead to preignition or hot spots. But apparently not? I would still prefer that OS's plugs would be a true long reach. They could be tightened more safely in the head. Does anyone have a clue why they are such short reach?

Ernie

Based on my own experience using Fox 5% nitro fuel in all my two strokes you can put a Fox Miracle plug in any of them with no problem. There is the odd exception such as my MDS .48 that demands a Fox idlebar plug but runs perfectly on it.

Whenever the subject of plugs comes up I like to refer to http://www.modeltechnics.com/glowplug/firepower.html because that lists actual tests on various engines with different fuels and shows the affect it has when going from a very cold to a hot plug. In most cases performance is acceptable on any plug but there are advantages to using the right plug if you're willing to experiment a little.

For Dar's benefit, it even shows that he's correct in saying that adjusting the mixture has an effect on the ignition timing because the colder plug always can be set leaner for peak revs. I'll admit I'd reserved my opinion on this until I had another look at the column for needle settings on that site just a moment ago. There you go, I'm willing to learn

As for why OS (and I believe Enya) plugs are an intermediate length, I have no idea other than that a plug length is best if it ends flush with the combustion chamber so if they make their engines so that only their own plug fits correctly...

Brian,


I am willing to learn as well.

...But when I am sure that my understanding is correct, I do give it my best shot to convince, as you would too, I believe.


This would mean using too hot a plug will necessarily increase the engine's fuel consumption, but not only that.
Since the position of the high-speed needle affects the mid-range as well, maybe when an engine is using too hot a glow-plug and the needle needs to be set excessively open, the mid-range and transition become flawed.

...So these 'defective' Super Tigre .90 carburettors may happen, just because the glow-plug is the A3 that was supplied with the engine... Not only too much nitro that North Americans tend to use.

Think about it.

What are YOU talking about?

Chuck,


As Robert DeNiro said in 'Taxi Driver', "You talkin' to me?".

Brian was...


He was referring to my distaste at the break-in instructions given by OS, in some of their engine manuals... in contrast to my acceptance of their glow-plug recommendations.

So, if a person disagrees with one piece of information from a source, they are supposed to disagree with everything from that source?

>>> As for why OS (and I believe Enya) plugs are an intermediate length, I have no idea other than that a plug length is best if it ends flush with the combustion chamber so if they make their engines so that only their own plug fits correctly... >>>


OS plugs don't fit right in their own engines. They leave threads exposed in the head. It doesn't seem right to me.

Ernie

Its easier to make a short reach plug work well in most applications than it is to get people to use the correct plug in a .10 or .15. Why are people so obsessed with glow plugs? Is there that much difference between them? Can anyone listen to an engine and tell what plug is in it? Why does a high end mfg. like Jett recommend cheap K&B plugs. After reading these posts it appears that an engine simply will not run without an OS F plug.

Kweasel,


The K&B-1L is a medium heat glow-plug, just like the OS #8, the Enya #3, the MVVS/Novarossi C6, Etc.

The fact that it would last just as long and costs significantly less than the OS, just makes it much more attractive to buy.


It is definitely not a 'cheapie' glow-plug and the more expensive ones, from OS/Enya simply have no tangible advantage, to justify the premium needed to buy them.

Ernie, if those exposed threads got hot enough to cause pre-ignition they would be gone in a very few seconds, pre-ignition caused by red hot spots whether carbon or metal usually has disastrous results in short order. On the opposite end of things the Fox Miracle plug sticks way down into the combustion chamber, in fact I didn't think a Miracle plug would work in my RCVs but they fit just fine. I have an ABC Fox .74 that was contrary and would quit about half the time during acceleration at about 4,500 rpm, I noticed that the plug was far above the combustion chamber in the glow plug hole. I countersunk the plug so the entire idlebar was down in the combustion chamber, still a safe distance from the piston, that engine never quit again.

My experimentation with boat engines has shown that there is a difference. Twenty years or so ago, I was using mostly Fox short idle bar plugs for my smaller plane engines, such as a .25 FSR. Worked fine. I had taken a break from boat racing and had forgotten what I used in my 3.5 cc K&B outboard. One day I took the boat to the lake and inadvertantly put a Fox plug in it. No matter what I did, I couldn't get the engine to run right. It would run, but it just wouldn't come up to the speeds that I knew it was capable of. As a last resort, I removed the fox plug and put in a K&B 1S (older engine that needed a short plug). The engine came to life immediately. This is when I came to the conclusion that indeed all plugs are not created equal.

These days I use a variety of plugs, including OS #8 (2 stroke plane engines), OS F (4 strokes), McCoy MC-9 (high nitro boat engines), McCoy MC-59 (low nitro boat engines). I've still got a few Fox and old K&B 1S and 1L plugs, but I don't use them any more.