Engine Basics
 

OK,

I installed and am breaking-in a magnum .91 on my Kadet Senior ARF. This is my first 4-stroke engine ever. It seems to be fairly simple..it fires and runs like a 2 stroke, only quieter and better sounding IMHO.

Is there anything REALLY different about 4-strokes that I should know about? I already found out about 'kickbacks' or whatever you call it when the thing backfires and breaks the spinner or chicken stick.

Is it hard to tune a 4-stroke?

Why is the muffler so small?

any info will help...

THANKS!!!

RE: Engine Basics
 

Hi agexpert,

if you haven't already got one i would recommend a tach its a must,Hobbico makes a good one and its common at most hobby shops and allot of Patience when breaking them in.

The adjustments are very minimal much more toucher than a 2stk, run it on the fat side...typically what i do is tach it wide open and drop it back 2-300 rpms let it idle down as you would your 2 stk and slap the throttle there should be no hesitation and then fly it hi in case of stall on break in... good luck... Hope this helps

I run omega 15% 30/70 castor/synthetic blend fuel :D

RE: Engine Basics
 

The tach is a great idea, especially for 4strokes.

You will get advice that they're a waste of time, but truth is, they're an excellent learning tool. Anybody can hear rpms go up and down, but nobody has a clue what rpm they're hearing. And you'll never know from one engine to the next what they're actually turning. And no idea what the difference in rpm's is from one prop to the next. And no clue if an engine is running different if you swap it onto another airplane that resonates differently.

The tach will teach you stuff you'd never even think of if you didn't have it.

And after you've used it awhile, you won't find it necessary to use all the time. But you'll have it if you need it.

RE: Engine Basics
 

Senza has answered your questions. I would only ad that the reason for the castor oil, is to protect the engine in case of a too lean run. As you have noticed, 4 strokes make no sound change when they start to lean out, like a 2 stroke does. The castor oil still keeps lubricating, even when the engine temperatures get out of hand, so caster is good thing to ad for this reason. The reason the muffler is small is because 4 strokes make less sound.

RE: Engine Basics
 

--- and can tolerate more backpressure

RE: Engine Basics
 

That is correct. It was my opinion when I first started with 4 strokes some years ago. Just use the same fuel as you do with your two strokes.

Enjoy,

Jim

RE: Engine Basics
 

The 4-cycle engines create more torque and take a more speacle kind of fuel. the kickbacks are caused becaused it is such a large cylinder and since it has to compress alot more air it can kickback and actully run backwards but if you start it right (witch is not hard to do) you should not have to worry about it. plus the Magnum 91 is a great 4 cycle engine, i got mine (also my 1st 4 cycle) about 10 months ago and it has been a great little engine.

RE: Engine Basics
 

4-strokes don't need any special fuel. Most manufacturers recommend a fuel with at least 18% oil content, and most major fuel makers have at least that amount. I use Cool Power 15% which I run in all of my glow engines, both 2-stroke and 4-stroke.

Ken

RE: Engine Basics
 

HUH...[X(]

Four strokes do NOT require any special fuel. Are you kidding us or what.

Any decent 10% to 15% nitro with 18% oil is fine. Cool power, byrons and a host of others all work well. Do not run the oil marked for 4-stroke engines. They actually only have 16% oil and OS and Saito will not cover a warranty repair if that oil is used. Every 4-stroke engine I have ever used/worked on wants 18% oil. It does not matter if its all synthetic or a blend of synthetic/castor

I run Saitos, OS and YS engines, all 4 strokes. The only 4 stroke engine that requires anything beyond normal is the YS. The minimum nitro/oil content is 20/20 (20% nitro/20% full synthetic oil, no castor) for YS but if you have flown one you'll understand why. These are supercharged engines and love huge amounts of nitro. Saitos will also do very well on 30% nitro but OS and Magnum will start to detonate once you get over 20% nitro and will end up blowing themselves apart and backfiring thus throwing the prop

In all of my 4-strokes for normal sport flying I use Byron 15% nitro/ 20% oil which is a castor/synthetic blend (I beleive 2% castor/18% oil) I like more only than is needed because it's just the way I am. My OS's all have well over 200 flights annd one, the OS91 which is basically the same as the magnum 91, have well over 300 flights on it.

RE: Engine Basics
 

I'm about to break-in my first 4-stroke too, Saito 100. The book tells me not to exceed 4000 rpm for the first 10 min of operation to allow all parts to mate properly with good lubrication, & that due to the excessively rich mixture I may need to leave the glow heater attached. After that first 10 min run I can start leaning out slightly with each tank of fuel. Then it says that 40 min is considered sufficient time for normal break-in prior to first flight.

Now I'm one of those guys that darock is referring to. I can't tell by ear what 4000 rpm is. I thought as long as I kept it at about 1/3 throttle I should be ok. They show an rpm range of 2000 -11000 with a 14x6 on it so 1/3 should keep it under 4000 right? Without a tach, I figure all I got to work with is math. Because I don't have the experienced ear that most of you guys have.

So what do ya think is this theory gonna work-out ok for me until I can get a tach?

RE: Engine Basics
 

elenasgrumpy,
When I got my first 4-stroke I thought I could tell too. A buddy loaned me his tach and I realized that I didn't have a clue. So I invested in a tach. It really helps. Once you have some time with the engine you can start telling by ear what is good and what isn't, but use the tach until you get your ear trained. And besides, tach's are a good thing to have at the flying field. I don't think a weekend goes by that I'm not using my tach for something or other, especially when helping to troubleshoot engine problems for others. They're a great investment.

This is the one that I have and I really like it. It's $45.95, but it's also got an extended scale voltmeter in it that you can use to test your transmitter and receiver batteries with. I'm really happy with mine.
[link=http://www.horizonhobby.com/Shop/ByCategory/Product/Default.aspx?ProdID=HAN111]Hanger 9 tachometer/voltmeter[/link]

Hope this helps

Ken

RE: Engine Basics
 

Mark,

The problem you will have is allot of engines are already at max power before full throttle, especially 4 strokes and 2 stroke gas engines and if your mechanical throttle connection/resolution is off even a little then you may be well over 4000 long before 1/3rd throttle

How I break in my Saitos is set the needles like the book, start it and just increase the throttle to get a little higher idle, jsut a click or 2. You do not need to get to 4000 exactly, less is good in this case, besides at the settings you are gonna be at, you'll be burning around 2 ounces of fuel per minute

As an example my YS110 reaches max rpm at about 1/2 stick so I had to setup a throttle curve in my radio to make the stick reach full throttle by rpm at the end of the stick travel, but if you look at the carb, it's only open about 2/3rd's the way. My resolution is just about perfect. At full stick, before I set the curve, my carb had just went to full open

2 stroke gas engines are even worse.

A tach is a must for a 4-stroke.

RE: Engine Basics
 

That's what I was trying to say, that I CAN"T tell the difference. That looks like a pretty good tach/volt meter for the money, I'll have to get one.

Bill the new radio I got will do the throttle curve set-up, but I gotta do alot of reading first to learn how to drive this radio. I think for now I will do as you suggest & just barely raise it above idle. I just gotta hear the thing! ;) I'll make sure I keep it nice & fat & stay off the throttle, until I can get this radio figured out. Thanks guys.

RE: Engine Basics
 

elenasgrumpy,
I like the tach H9 makes its looks good that RCKENS mentioned, but if money is an issue the [link=http://www.hobbico.com/fieldequip/hcap0401.html]Hobbico[/link] tach is only $25.00 its a great way to start.

the first thing i do when i use to assemble a plane and bought a flight pack, I would remove the battery and replace it with a 4.8 nmh 1600 or better you can fly almost all day with it,and i would install a volt watch meter in the canopy to keep an eye on things.

I realy never used a volt/load meter until i got in to gas planes when having one was necessary to check 3-4 battery's at a time it's a must before flight.

I would highly recommend the investment into a good battery cycler,if you don't already have one, this gives you a good peace of mind knowing you have a good battery in your Baby!

Heres a link to the [link=http://store.xtremercproducts.com/voltwatch.html]Volt watch[/link] meter clean and neet

RE: Engine Basics
 

SENZA, Yes! I just saw that in another thread like just yesterday I think. That is a great deal for a lousy $10 you can't go wrong there, I definitely plan on ordering some of those, as in one for every plane I own!;) I still can't believe the price of that thing, what a deal.

The flight pack that came with the radio I'm running in this current project came with an 1100 mah battery, not too bad I thought. Ya know I do have a cycler but it is an older one & just does NiCads. I need a new one, because I use Nihm, & Lipos too. If I could I'd like to get away from NiCads alltogether. Thanks for the tips, I'll take a look at that tach you put up too.