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Old Jul 15, 2005, 02:56 AM
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ring or abc engine

Which engine is better and the pro and con
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Old Jul 15, 2005, 07:03 AM
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ABC =
Cheaper (usually) to buy due to easier adaptibility to mass production (fewer parts count).
More power (usually) than comparable ringed engine.
When it wears out, you replace the entire head and piston assy.
Break in is CRITICAL; improper break in can ruin a brand new engine from overheating.

Ringed =
More expensive.
More forgiving of abuse (dusty environment or hotter running, etc.)
When worn out (compression loss), you can usually just replace the ring (cheap) a couple of times before needing cylinder or piston replacement.
In general, longer lasting than an ABC engine. It will usually go longer before needing to replace anything due to wear.
Not much break in necessary other than to run a little rich for a couple of tanks.

That's the basics.

Highflight
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Old Jul 15, 2005, 01:14 PM
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Yup, hes right . But, ringed engines ,do require that you run the engine rich for the first couple of tanks, 1 lean run, can damage the engine.
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Old Jul 16, 2005, 07:46 PM
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I'm not sure I undestand HF's comment about damage from overheating during breakin of ABC engines.

Just the opposite is the danger in breaking in an ABC engine, in my experience (and according to ABC engine manufacturers). An ABC engine needs to be run at or near it's normal operating temperature from the first start so the proper running clearance between the piston and top of the tapered cylinder can be obtained. The sleeve typically expands more than the piston while warming up to achieve this. Running an ABC motor too rich (slobbery 4-cycle rich) won't allow it to ever reach that temperature, and will rapidly wear out the characteristically tight fit at the top of the stroke. This will result in a new engine that will run like crap due to loss of compression.

If an ABC engine is run too lean, it generally blows the plug or just sags and quits. I've never seized an ABC engine from a lean run, unless a conrod or something let go internally as a result. Can't say that for a ringed engine.

Rick
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Old Jul 16, 2005, 10:58 PM
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yup, your right. :P
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Old Jul 18, 2005, 10:47 AM
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Quote:
Originally Posted by ElectRick
Running an ABC motor too rich (slobbery 4-cycle rich) won't allow it to ever reach that temperature, and will rapidly wear out the characteristically tight fit at the top of the stroke. This will result in a new engine that will run like crap due to loss of compression.
This is a myth, busted by downunder. Here's his mythbuster.
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Old Jul 18, 2005, 11:13 AM
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Quote:
Originally Posted by ivanc
This is a myth, busted by downunder. Here's his mythbuster.

It wasn't a myth when I ruined a brand-new OPS marine racing engine by breaking it in too rich. Broke the bottom end of the conrod out, but not before it galled up the top sealing edge of the piston and seized it.

Perhaps you can get away with it on SOME ABC engines, but my experience is that there is a significant variation in the amount of taper and "pinch", and in material composition for the piston and sleeve among different engine brands and models. I had a Picco .90 marine that you darn near couldn't turn through TDC cold by hand, even after break in. I mean it was SQUEAKY tight. Some other ABC engines I've had had a pretty mild fit at the top, relatively speaking.

I'm not disputing the findings of that guy on his own particular engine, and you all can break in and run your ABC engines sloppy rich as a result of them if you like, but for me, I'll defer to the wisdom of the people who designed, tested, and manufactured my engines for advice and recommendations on break in procedures.

I'm not about to play Russian roulette with an expensive ABC engine for no good reason. Besides, why take a chance on voiding the warranty in case something lets go inside during break in by not following the manufacturer instructions?

Isn't it odd that no maker of ABC engines that I know of recommends a sloppy rich break in on them?

Encouraging or even suggesting it's OK for others to ignore the manufacturer's recommendations for their break in procedures is irresponsible, IMHO.

Rick
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Old Jul 19, 2005, 02:41 AM
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Should I go with a reliable ring engine or a more power abc engine. I trying to decide between o. s. 46fx or 50sx. thanks
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Old Jul 19, 2005, 09:47 AM
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There isn't much difference as far as daily operation of ABC vs. ringed goes. It becomes a choice between more or less power, shorter or longer break in, and maintenance/repair costs.

Here are a few differences off the top of my head:

ABC's in general have more power than the same sized ringed engine, since they are virtually always of the Schneurle port configuration and the compression seal tends to be better (no ring blow-by). Many ringed engines are Schneurle ported too, however.

The ringed engine is less tolerant of a lean run than an ABC.

Ringed engines tend to build up crud in the ring grooves that can interfere with the ring's seal.

ABC engines need very little break in compared to a ringed engine.

The ringed engine has to be run in until the ring seats in the piston and cylinder to create a compression seal.

ABC's tend to be more expensive to buy and obtain repair parts for, as the piston and sleeve really need to be replaced together as a matched pair to get the right fit.

I prefer ABC engines because I have used them for many years, but you can't go wrong either way for sport applications.

Rick
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Old Jul 19, 2005, 07:45 PM
Flying RC since 1974
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Joined Dec 2002
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Umm...Rings tend to come in high end ball bearing (BB=Ball Bearing) engines, and a properly cared for BB engine will outlast a sleeve bearing engine, almost certainly, plus they usually generate more power and also can be renewed with replacement of bearings and soforth when they do wear out. Many people then, mistakenly think their first motor ought to be a good quality ringed or ball bearing engine like a 40 or 46 FX/AX, or that neat little 32 SX or even a nice four stroke "because they will use it on their second plane". Nice idea, seems economical and like planning ahead, and for some, it's even the right thing to do. BUT think about why you have a trainer and what your are really trying to do.

YOU ARE TRYING TO LEARN TO FLY, and there is only one way to do that. FLY. FLY LOTS.

Your plane is almost certainly going to take a dirt bath, or several before you are fully proficient, and even after you get pretty good, your plane is still going to take a few dirt baths if you are pushing yourself. When this happens, you are going to end up with an intake full of dirt, and frankly, if the plane is otherwise undamaged, you are not going to want to pack it in just so you can go home and tear down the motor.

You want to buy the engine that is low cost and most forgiving of abuse. This would be a sleeve bearing ABC motor. Here's why.

With a plain bearing engine, you turn the model upside down and hit the engine and carb with a few strong squirts of fuel from your pump to rinse off most of the dirt. Then, you replace the prop and double check that all the parts are still properly attached. Then you fire up and you fly some more.

This is of course, an ABSOLUTELY AWFUL THING TO DO TO YOUR ENGINE, but frankly, a plain bearing engine can handle it because although ther are a few precision spaces inside, there really aren't any where dirt can lodge and destroy the motor. The dirt and crud will blow on through the engine, leaving only a tiny bit of extra wear behind.

Meanwhile, you are flying and that's what it's all about, FLYING! Given our tight schedules and limited liesure time, you can trade a bit of extra wear for the opportunity to do more flying and that is more valuable than a, frankly, pretty cheap motor.

On the otherhand, ringed BB engines have lots of precision spaces; the bearing races, the ring grooves, etc, where dirt can get stuck and pretty quickly score the bearings, piston or the cylinder sleeve. Plus they are more expensive. When a BB engine takes a dirt bath, YOU MUST remove it from the plane, tear it down and make sure it is absolutely clean inside before you fly again. If you want to take the time for that, great, go for it. But in my experience, the average beginner wants to fly, and fly ALL THE TIME, not mess around with cleaning engines.

Trainer planes get dumped in the dirt and then patched up with strapping tape and CA and put back into the air again. Frequently, they look like flying death with a hangover. But who cares? The point is to get airtime and you can't do that if you are fussing with a precision engine.

So, buy the cheapest engine from a reputable manufacturer that will haul your trainer into the air. Beat the daylights out of it and save the top end engine for that third or forth airplane when your landings are all so perfect that the only wear your plane suffers is worn tire tread.

My first engine, an OS plain bearing .25, bought in 1974 (31 years, sheesh, where did they go?) Was treated this way, and guess what? Beat up old thing still rattles along and can still haul a Kadet Seniorita around.

So, Hollywood, my advice is forget the 46 AX/FX or 50 FX/SX, and get a 46 LA or similar. It will run right out of the box, you hardly need to do anything special to break it in and you can use it, abuse it, and keep it around to use in your "winter beater" airplane after you have moved on to that Corsair you've been drooling over.

Anyway, have fun, Thats the main thing.
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Old Jul 19, 2005, 07:59 PM
Flying RC since 1974
Del Norte, Colorado
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Oh, and while it may or may not be true that a slobbery rich run will ruin your brand new ABC engine, there is no good reason to do that slobbery rich run. Run it the way the manufacturer suggests and you will end up with a good running engine.

Frankly, I'm not sure you even need to baby the new ringed engines the way we used to (extra castor oil, hours of tedious bench running, persnickety prop selection). Modern CAD design, precision CNC machining and advanced manufacturing practices make new engines pretty darn good right out of the box. Still, a bit of extra care for the new baby...
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Old Jul 20, 2005, 10:41 AM
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Another take on ABC engines is that they are made to incorporate a certain taper between the piston and the cylinder that is designed, and understand this correctly, to provide for proper clearance when at operating temperature.

During breakin of an ABC engine, you should always keep the revs down to high idle for about a minute in order for those temps to come up before running it up. If you start a brand new ABC engine for the first time and immediately go full power, you're going to be shaving some metal off places that wouldn't happen to a properly warmed up new engine.

Highflight
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Old Jul 20, 2005, 10:52 AM
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Agreed. The hours of bench running used to be the norm years ago for engines with lapped iron pistons running in steel sleeves, like Foxes and some Enyas. Those things took a long time to break in.

Modern engines really only need to break in just long enough to knock down and burnish the microscopic high spots on the machined surfaces to loosen the running fits and clearances up a bit. Break in running also serves to get the screws stretched (if they're going to) to their final heat stabilized length.

With most of the ABC engines I've ever had, I never ran more than one or two tanks through them before I went flying with them. Of course, the first few flights were made with the needle slightly rich from optimum, just enough to leave a nice smoke trail.

Rick
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Old Jul 22, 2005, 07:09 PM
Flying RC since 1974
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Quote:
Originally Posted by ElectRick
...Break in running also serves to get the screws stretched (if they're going to) to their final heat stabilized length...
Rick makes an important point that lots of beginners need to know about.

After about 20 runs, you may find that suddenly your engine has gotten really unreliable. You find your engine is crapping out on take off, or when you gun it to go around after a blown landing approach, the motor dies. Seems like this effect kicks in about the time that beginners are ready to start solo flying and it really busts up your confidence.

Engine components move around a lot when they heat up and cool down, and this can cause the head, backplate and/or carb mount screws to work loose. This may allow air to leak in, or fuel/air mix to leak out where it ought not. The result is an unreliable idle and/or needle valves that just refuse to stay set.

After about ten motor runs, check every screw and bolt. You will often find that you can snug them all up a quarter turn or more. Similarly, check the muffler and engine mount bolts. They work loose too.

I generally find that once this initial loosening and retightening happens, everything stays tight for hundreds of subsequent flights.
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