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Old Jul 17, 2008, 08:28 AM
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2 or 4 stroke

well, im thinking about getting a plane and it says it will take either a

.15- .25 cu in (2.5 -4cc) 2-stroke or a
.30 cu in (5cc) 4-stroke

my question is what is the difference between a 2 and 4 stroke engine?

are there any advantages or disadvantages for either
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Old Jul 17, 2008, 09:57 AM
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In a nutshell:

2-stroke is cheaper, less complex, and often more user friendly.

4-stroke sounds better, spins a larger prop for a given displacement, and is much quieter.

These are just my opinions, of course, others may disagree.

Erik
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Old Jul 17, 2008, 10:44 AM
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I'm interested in this topic too. In my case, I'm interested the new tt 75 four stroke or a saito 82 (btw, how do the older saito 80 compare to the 82) or a .61 or .7? two stroke (I think os, tower and gms all have .7something engined in a .61 case).

This would likely go in this plane: http://www.horizonhobby.com/Products...ProdID=HAN4675

Can you have a decent smoke system with 4 strokes (I've seen varied opinions on this)?

Thanks, Rodney
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Old Jul 17, 2008, 10:49 AM
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I believe that it would be your first plane so 2stroke engine would be better choice.

In your particular case the only advantage of fourstoker is coolness (having that small flying fs!)
and a bit more static trust(a .25 spins props around 9 inch compared to a .30fs that is up to 10inch dia.).

In general I agree with justeric, but .30 is to small to bring all benefits of a 4stroker.

Some information about plane could help to determine best engine option for it.

Regards!
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Old Jul 17, 2008, 11:36 AM
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Here are two excellent .30 sized fourstroke engines, they will turn a 10x5 or 10.5x5 Graupner prop at 10,400 rpm and sound like a big engine doing it. Fourstrokes generally are more reliable in flight than two strokes, seldom having a deadstick other than when out of fuel.
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Old Jul 17, 2008, 12:14 PM
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I have always had a much easier time starting a 4-stroke. They seem much more forgiving with regards to priming, and are easier to flip over if you are doing it by hand as they have a lower compression.

I have, however, always had to make sure all my bolts are good and tight, as the 4-strokes rattle the fillings out of your head, especially for the first gallon or two of fuel. They get better with time, and making sure the idle needles are set correctly.

The only frames I run 2-strokes in are the go-fast varieties. If SPEED is your thing, then stick with a 2-stroke for the higher RPMS they generate. 4-strokes give more "torque", which provides a faster spool-up for acceleration in "3D" type maneuvers, and pushing a larger prop. Otherwise, I just prefer the Saito 4-stroke in general. You have to occasionally check your valve clearances, but that's no big deal, and I rarely have to adjust them. (it's easier than it sounds)

Plus: I'm a sucker for style! You can't beat the sound of a 4-stroke. It makes you feel like one of the "big boys" :P
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Old Jul 17, 2008, 02:58 PM
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Shaz, I don't know where you get your fourstrokes but if you set the LowSpeed needle correctly they don't shake at all.
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Old Jul 17, 2008, 07:24 PM
Zor
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Quote:
Originally Posted by rodneygt

Can you have a decent smoke system with 4 strokes (I've seen varied opinions on this)?

Thanks, Rodney
Rodney

You may want to have a look at this.

http://www.macspro.com/smokesys.asp

Zor
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Old Jul 17, 2008, 08:39 PM
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Quote:
Originally Posted by Zor
Rodney

You may want to have a look at this.

http://www.macspro.com/smokesys.asp

Zor
Zor,

Thanks, I will have to look at the video when I get back to my office and my high speed connection.

Rodney
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Old Jul 18, 2008, 12:00 AM
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Hey rc manic101.
I have four strokes in all my IC engine Planes.
I think the sound of a four stroke purring away up there is unbeatable
and I like the broader torque curve that a four stroke provides.
Also my flight times are longer than those with 2 stroke engines.
Those three points are enough to keep me a four stroke Fan.
Good luck which ever way you go.
Steffan.
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Old Jul 18, 2008, 03:58 AM
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Hey guys, rc maniac is just a kid, he has to build up some flying time first, crashes verry possible.
So adjusting valve clearances is to much excercise, and repairing a 4stroker after any serious damage is more expencive than buying a new 2stroker.
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Old Jul 18, 2008, 05:14 AM
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Quote:
Originally Posted by Nikolash
Hey guys, rc maniac is just a kid, he has to build up some flying time first, crashes verry possible.
So adjusting valve clearances is to much excercise, and repairing a 4stroker after any serious damage is more expencive than buying a new 2stroker.
Actually, I've found 4-stroke engines *cheaper* to repair than 2-strokes.

I buried my Saito 100 so deep in the (hard) ground that all you could see was the occasional glint of the intake manifold. When I hauled it out, all I had to do was replace the pushrods and tubes ($20 in total).

By comparison, I recently buried an ASP (Magum) 52 about the same depth and hit snapped the carby right off and also broke the muffler. Total cost (if I'd bothered to repair it) over $50.

The "up-front" carby on your average 2-stroke is far more vulnerable than the "tucked in behind" carby on a 4-stroke and those carbs aren't cheap.

However, if you're flying over tarmac, chances are that a good smack will end up breaking a crankcase in either case so a 2-stroke might well be cheaper to "write-off" than a 4-stroke.
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Old Jul 18, 2008, 02:57 PM
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Wait til you see what a Saito 91 cylinder costs. I have replaced three for club members. One stripped out a helicoil twice and the other smacked his into the ground and tore of a valve mount. A cylinder cost $100. The helicoiled one couldn't be helicoiled again. After I replaced the cylinder he knocked of a rocker arm. Had to replace the cylinder again.

If you damage the head of a two cycle it is considerably cheaper. Most of the parts for a four cycle are expensive and 4 cycles are more expensive to repair. About the only parts that are on par with a 2 cycle are bearings. Two cycles are much easier than 4's for a beginner. A good 4 cycle will cost at least twice what and equivalent 2 cycle costs. Sooner or later a guy starting out is going to whack an airplane into the ground. better to break a cheaper and easier to repair 2 than a 4.
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Old Jul 18, 2008, 05:34 PM
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Quote:
Originally Posted by usna71
Wait til you see what a Saito 91 cylinder costs. I have replaced three for club members. One stripped out a helicoil twice and the other smacked his into the ground and tore of a valve mount. A cylinder cost $100. The helicoiled one couldn't be helicoiled again. After I replaced the cylinder he knocked of a rocker arm. Had to replace the cylinder again.
But the Saito is a little different to most 4-strokes insomuch as the cylinder and head are a single unit -- hence the expense.

With an ASP/Magnum, OS or TT 4-stroke, the head is a separate item that is much cheaper to replace.

Quote:
If you damage the head of a two cycle it is considerably cheaper.
Apart from people over-torquing or cross-threading glowplugs, I don't think I've seen anyone irreparably damage a 2-stroke head. Even when I did an inverted landing on the tarmac with a TT42GP, it simply broke the plug and "chamfered" the front. A few minutes work with a file to tidy up the mangled fins and a new plug was all it took to fix that.
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Old Jul 18, 2008, 07:00 PM
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OS 91 Surpass head-$70.00 OS91FXhead- $47.00

OS Surpass 91 muffler-$64.00 OS91FX muffler-$47.00

OS 91Surpass carb-$85.00 OS91FX carb-$61.00

Check it out, 4 cycle parts are considerably more expensive than two cycles and the 4 cycle price is a BUNCH more.

As a beginner it makes more sense using a less expensive, cheaper to repair, and easier to use engine.
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