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Understanding Glow engines ????

Old 11-20-2014, 04:45 PM
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jayd3
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Default Understanding Glow engines ????

Hi all
I'm a guy who wants to know all about glow engines how to figure out why a new engine is a dog that won't start an run well, how to tune or rework to fix it or for greater performance stuff like that.
So I think I need to get and understanding of timing,porting, compression, glow plug heat ranges ........
Like why do small engines not just run better but often absolutely need high nitro fuel to run at all ? does raising the compression mean you need less Nitro? what affect does porting have on all this ?
I know a bit about engines both 2 and 4 cycle from auto mechanics study but gasoline is a bit different and 2 cycle porting is not really well explained other than it;s how fuel and air get into the combustion chamber since there are no valves in the head.To my understanding of 2 cycle gas engines a reed valve engine is slightly better because it offers crankcase sealing, and better fuel lubrication control typically bringing the fuel lube mixture right over the crankshaft rod journal. Reeds also allow more complex porting in the cylinder I think ?????

The more I think I know the less I know I know!

Jay
Old 11-20-2014, 07:53 PM
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DerFly
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Jay,

Read, read and read some more.

Try to understand the numbers, why more (or less) is better.
Why does a designer do this?
What is the purpose of that engine?
Is it built to a cost? (More than likely)
What improvements are made from one model to the next?

etc., etc.

DF

http://sceptreflight.net/Model%20Eng...sts/Index.html
Old 11-21-2014, 03:55 AM
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Jay,

Some of what you say is true, some half true and others not true.
Probably the first thing to learn is there are no absolutes.
As DF says read, read etc.

You can consider starting with Gordon Jennings Two Stroke Tuners Manual. (Google it).

Next get a range of engines from low cost to high to determine the difference in performance, given the target buying audience for each. eg a low cost engine might outperform a high cost, but probably won't outlast it.

Good luck - it'll be an extensive study area for you.
Old 11-21-2014, 04:26 AM
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That's simply too much to take in all at once. Get a plane and an engine and learn all about that engine. An LA .46 would be a great starting place, it's a basic two stroke, straight forward, very user friendly, very reliable and long lasting.
Old 11-21-2014, 07:17 AM
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That is a lot to learn. I suggest getting a engine test stand and use it to start with glow engines. Then you can learn how to start them and adjust them in a ideal environment and not inside of a airplane where other factors come into play. Every engine is different and the solutions to fix one engine may not work on another.

A engine requires three things, fuel, air, and a source for ignition. If it gets those it will usually run. To run good of course is another matter.

Last edited by earlwb; 11-21-2014 at 07:19 AM. Reason: add more info
Old 11-21-2014, 08:51 AM
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For model engines, there are a lot of books available.

You may be able to locate the old RCM publications, "The RC Engine" by Clarence Lee...several volumes available

"All About Engines" by Harry Higley

"ULTIMATE NITRO ENGINE GUIDE", "R/C AIRPLANE ENGINE GUIDE", and "POWER: BEYOND BASICS" all published by Air Age (Model Airplane News)

There are also other books out there, but many may be out of print.
Old 11-21-2014, 03:13 PM
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Glow engines are something of a contradiction in that they're about as simple mechanically as possible but they get quite complicated when you dive into the nitty gritty of how they work and the tiny details make for a never ending learning curve. Reading articles and books gives a good start if you can get a hold of them but seeing you're asking on a forum means you'd probably want some quick answers but be aware that there are many different opinions so treat with caution, from me too . So to give my answers to a couple of questions you asked.....

Small engines and nitro. It's a myth that very small engines won't run without nitro, at least down to the .049 size. I know because I've tried them on zero nitro and they all ran perfectly, just like larger engines. Naturally they give more power (revs) with nitro but the same can be said for any size engine (within limits of compression but that's another discussion).

Cylinder porting. Because it's obviously symmetrical (disregarding Desaxe,another discussion ) then it's a compromise compared to 4 stroke timing and, within limits, not really all that critical for sport type engines. Given that it's a compromise it's surprisingly efficient or we wouldn't be getting the comparatively massive power they develop.

Glow plug heat range. This gets into a fairly complicated area of exactly what the best ignition timing is for a particular combination of compression/fuel/prop load etc but suffice to say for now that it's not got much to do with element temperature as its ability to ignite the mixture given the conditions inside the combustion chamber. A "hot" plug ignites it more easily than a "cold" plug. Not to be confused with hot or cold spark plugs where it's used to indicate how well it keeps carbon from building up on the electrode.

Compression. A curly one because compression ties in with glow plug heat range and it's the combination of the two that determines when the mixture will fire. Higher compression will fire sooner with the same heat range plug. But it also depends on how much nitro is in the fuel. Straight methanol can handle extremely high compression (~17:1) but straight nitro is limited to ~6:1 before detonation. A mixture of the two then needs a compression somewhere between these two extremes to avoid detonation. It's a fact though that the higher the compression the more efficient the burn is so by using nitro you limit the burn efficiency but this is more than made up for by the extra power (heat content) released at the expense of fuel consumption (air/fuel ratios, yet another discussion!).

Reed valves. These went out of favour maybe about 40 years ago and the best of them was probably the Cox Olympic ( http://sceptreflight.net/Model%20Eng...20%281%29.html ) but these were replaced by the crankshaft induction Tee Dee which gave a big jump in performance although still using similar cylinder porting.
Old 11-21-2014, 06:27 PM
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downunder, that was an excellent summary of some very comprehensive, complicated subjects in a few lines.


Mark
Old 11-22-2014, 10:34 AM
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jayd3
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Thanks to all who have responded especially downunder
I am a firm believer that a good understanding of the basics is the key to success in fixing tough problems: understand how it is supposed to work and you can understand what is wrong (eventually lol).
I'd like to find the books by CF Lee , I have a K&B 61 Mr lee customized for me some years ago, I bough it in like new condition hardly even a stain on it but it ran extremely poorly so I sent it to Mr Lee he found the major problem was and assembly Error where a cylinder head spacer had been added that was not needed.

Thanks for the discussion and resources.
Old 11-25-2014, 12:10 PM
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JayD3,

For starters, get an engine to "play" with if you don't have one now. Use a test bench. These have been mentioned already.

On a test bench, if anything starts going wrong, you can yank or pinch the fuel line off and stop the engine NOW.

Read and apply the mfr's instructions. They put a lot of R&D into their products, and won't tell you things that will ruin their engine in your hands, and their reputation in your mind.

Today's RC engines generally have clear, simple and understandable instructions, both for the engine and the throttling. You will learn the by doing. The idea of chopping up a highly developed engine for some specific purpose is unlikely to succeed unless and until you have extensive experience with it in plain vanilla form, the skills involved to prevent harming the engine's performance and reliability, and THEN know exactly what it is you want changed, and how to attempt doing it -

- more raw power (unlikely these days, most have ample power),
- or a lower idle (adjustments, choice of fuel/plug/prop can go a long way for this),
- better throttle response (see previous comment.)
- some other specific result...

Luck!
Old 11-29-2014, 03:13 PM
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jayd3
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I have several engines and a test stand
The engines range from .020&.024 to a Lee custom .61 I even have an old but little run fox 36 fitted with a OS 35 carb that runs well, I ran the OS 35 till it was completely worn out with an egg shaped rod and little compression put a better rod in it but no power.
It's the old small ones are the most trouble! OK Cubs, Some Cox trying to figure out why some start and run good and why some are dogs.
Thanks
Jay
Old 11-29-2014, 05:00 PM
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downunder
 
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Originally Posted by jayd3
I ran the OS 35 till it was completely worn out with an egg shaped rod and little compression put a better rod in it but no power.
That sounds as though you've got (had ) an old OS 35 Max-S which has a cast iron piston running in a steel sleeve. Engines with this type of construction thrive on all castor fuel or fuel with at least half the oil being castor. Normal minimum oil content is 20% but 25% is safer. However these particular OS are renowned for wearing out the rod if less than 25% all castor is used. I suspect you've used an ordinary RC fuel which has ruined both the rod and piston. Think of this as being part of the learning curve about glow engines .
Old 12-01-2014, 05:38 PM
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jayd3
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I suspect your right about the OS it did have the iron piston and steel sleeve, I did run the red castor fuel but did not supplement with extra oil, should I use cherry flavor ? lol
Wonder if the old Fox also needs more castor ?
I would think a blend of synthetic and castor would give the best lubrication ? I'm thinking CF Lee recommended adding somthing like 2% minimum castor to synthetic fuels .
My 1995 lawn boy needs 32:1 and newer 2 cycles use 50:1 the reason there is newer engines are made with harder metals, and better machining the smoother and tighter tollance the less and thinner oil is needed, we see this with motor vehicles now calling for 5W 20 and a few even 0W20 motor oil. So is this the same situation with the old OS ?

Thanks
Jay
Old 12-02-2014, 03:51 AM
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Engines like Fox and old OS were designed for all castor oil. Anything with an iron piston should never have synthetic oil used in them as the varnish produced helps the piston seal better. Synthetic oil washes away the varnish and the piston seal with it.

As far as the thinner oil weights in automobile engines - this is due in part to thinner oil makes more power. Add in cheaper manufacturing tolerances and such, and you get modern engines with piston slap. You never heard this phenomenon when using 10w30.
Old 12-03-2014, 12:34 AM
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Jay and 1Q,

The older engines were designed when the only usable oil was castor. Mineral oils don't blend with methanol. In the early 1970's we began to see synthetics like UCON 6225 (I think it was.) CL racers, at least, used them and swore by them almost as much as they swore at them for their tendency to dye anything it touched a deep blue or purple. (Skin and clothing included...)

Synthetics then developed pretty quickly, including a line of K&B 100, 500 and 1000 with "X2C" (...a cutesy suggestion of ecstasy...?) claimed as a better oil than castor. It may have been, but there were reports of (iron in steel) engines losing compression drastically when a K&B X2C fuel was used in an old, castor-varnished engine. (I had at least one such.) New engines, even of older design, didn't seem to have that problem... (NB: Jim Thomerson has often mentioned that he has several stock Fox 35s (or other iron in steel engines) broken-in from first run on synthetic blend fuels that do very well... It may be that initial 'varnishing' on all-castor fuels interferes with that....)

Discussions on various sites have mentioned certain highly developed stunt (and other purpose) engines that do NOT do well on fuels with ANY castor. At the other end of the precision spectrum from the inexpensive weed-whacker engines that use 50:1 oil fractions, but similar effects. In a very high precision engine, materials and clearances are very carefully matched; ANY buildup of varnish or other microscopic coating on P&L can disrupt that precision in either or both of two ways: Clearance change which interferes with matched expansion, or coating effect on heat exposure/rejection interfering with reaching the design spec heating and expansion conditions.

I'm neither a metallurgist nor a lubrication scientist, but I've heard - and believe - that any kind of cast iron is microscopically porous. Heated castor oil can do funny things, apparently. Like 'wick 'into microscopic porosity. A fairly well known example: Castor runs TO a heat source, while mineral oils flow away. I've (supposedly) checked this. On a flat 'plate' of iron heated from below by, say, a propane torch, a drop of castor at the hot spot did thin and run towards the hotter area; mineral oils (SAE30 or so) thinned and flowed away from the hot spot.

Further, the modern synthetics ARE excellent lubes, AND detergents to carry burn residues off the metal surfaces. For an engine 'conditioned' by hot castor wicking into porous cast-iron, the slick surface provided by that castor is removed by the detergent effect.

That difference may be why castor was long thought the best oil for wear surfaces in our (and WW1 aircraft, and later auto racing) engines. (Hero driver in Europe in the 20's and 30's, Tazio Nuvolari, became ill and, I believe, eventually died of complications from the castor fumes he breathed in the exhaust gases. Many WW1 fliers also suffered the consequences of excess castor oil exposure. Messy!)

I don't know much more about modern synthetics, except that either Dave Gierke's book on 2-stroke model engines, or his series in Flying Models, (late 1970's as I recall) did cite the burning point temperatures of castor and the available synthetics Again, AsIr, castor held on as a lubricant to just about 500°F, while the synths of the time had burned away at less than 470°F.

AND that combustion chamber temperatures occasionally DID reach into the range between those two values. Academics? Oil above the piston does not contribute to lubricating the piston in the power stroke motion. If, however, the oil remains as a very hot vaporized form of its room temperature state, that heat is carried and ejected when the exhaust port opens. Think... absorbing heat from a hot object and removing it to somewhere else is a good definition of cooling, no?

If the 'hot oil' in the combustion residues was a synthetic oil, and the magic "burn temperature" was reached or exceeded, that oil no longer exists to carry heat out the exhaust. In fact, however poor a heat yield it provides when it DOES burn, that heat is added to the heat to be got rid of...

For our uses, ferrous (iron and steel) engines enjoy the lubrication at temperatures that burn off synthetics. BUT engines designed around the heating and expansion figures of optimal use DON'T need coatings that disrupt those values.

Dealer's choice...
Old 12-03-2014, 12:58 AM
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...To add a bit that may be "politically incorrect" these days: The "burned-off" synthetic oils in the combustion exhaust gases make for a cleaner - less oily - exhaust plume.

In other words, less oil slop on the model...

The non-PC side of this? Many RC "Sport" fliers don't like to scrub down their models after a few flights. Burned-away oil does not coat the model... (Is this a part of the movement to electrics?)

"To heck with the machinery, don't waste time (or ecologically questionable cleaning solutions), on messy oil residues!"

Fewer paper towels!

Save the trees!

Save the planet!

(...only partially tongue-in-cheek...)
Old 12-04-2014, 04:46 PM
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I second the my wife knows everything !
Jay
Old 12-04-2014, 05:13 PM
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Default Castor Oil

Interesting discussion about engines that have had lots of castor not working with synthetic, i've seen articles saying engines run on castor fuel need de varnished every so often.
I was absolutely shocked to see the price of castor oil, one could buy a gallon of nitro methane for the same price !
Now I have not done extensive price shopping just the good old Ebay and their the cost is $50.00 a gallon +
If one mixed the 20 -25% castor as many suggest for old iron piston and 1/2 A engines your adding a huge cost to a gallon of fuel .
adding 10% is 12.8 OZ 20% is 25.6 OZ of pure castor or as a ratio 4:1 and 3:1 that is a huge amount of oil and expense
for 1/2 it would be far cheaper just to buy the COX fuel.
Since castor does not burn well that is a lot of byproduct, but then I have personally witnessed the amount of oily byproduct from 1/2 engines they slobber like a Saint Bernard, one would need a drain on a muffler or it would soon be filled with oil, perhaps why so few ever had mufflers?

Jay
Old 12-05-2014, 08:52 AM
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Castor oil from ebay is likely 2nd pressing oil intended for soap making. 2nd pressing oil is not ideal because it contains the "gum" that the 1st pressing doesn't have. I was getting 1st pressing castor oil from SIG for $23/gal but they recently raised their price to $38/gal. SIG sells Klotz Techniplate synthetic for the same price as castor now. I now source castor oil from S&W fuels for $25/gal.

The residual oil may accumulate in the muffler after the engine is shut down but that amount is pretty small. The oil gets blown out the exhaust while running. The small 1/2a engines do not run as well with mufflers because they hurt performance quite a bit and as it is for their size, they don't make a lot of power anyway. Taking a 10-20% hit on power is a lot for those tiny engines.
Old 12-05-2014, 08:58 AM
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Jay, castor does mix well with synthetic oils. It isn't actually a byproduct. It's an oil from a bean and is all organic I suppose. The lack of burning is a good thing for your engines. I think castor is much cheaper than you found on Ebay where you checked.
Old 12-05-2014, 01:35 PM
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Castor oil costs less than the synthetic oils do. The varnish from castor oil is not a problem for the vast majority of engines. It is only a thin layer. But the racing people tend to remove that varnish as they are going for more speed of course. Every extra RPM counts.

But some old heavily used lapped piston engine may need that varnish layer inside on the cylinder. Removing the varnish may result in the engine losing compression and losing power then. Since it is well worn, the varnish may be helping it this case. A new engine wouldn't have the problem of course.

Castor oil can vary a lot in prices, One should shop around for it.

The trick to keeping the varnish down is to avoid running the engines that lean. Unless you are racing of course.
Old 12-05-2014, 05:10 PM
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Your right the Castor being sold on Ebay is mostly advertised for soap and candles, I should have known it is different from lubrication grade. I do remember guys in high school using medical grade castor oil in 2 stroke motorcycles not sure how that worked but they did it cause a sister worked at the hospital and it was free.
Old 12-05-2014, 05:13 PM
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when I said by product I mean the partially burned castor oil not the fresh.
Old 12-05-2014, 05:22 PM
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Default Book shopping

I've been looking for the recommended book "Two Stroke tuner's guide " by Gordon Jennings and found it for sale but at over $100.00 used

I'm now looking for a copy of "Two Stroke Glow Engines for R/C Aircraft " by C. David Girke


Jay
Old 12-05-2014, 06:14 PM
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Originally Posted by jayd3
I've been looking for the recommended book "Two Stroke tuner's guide " by Gordon Jennings and found it for sale but at over $100.00 used

I'm now looking for a copy of "Two Stroke Glow Engines for R/C Aircraft " by C. David Girke


Jay
Why not read it only for free? http://www.amrca.com/tech/tuners.pdf

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