What To Expect From A 4-Stroke
 

I'm building a Great Planes Gee Bee and I'd like to go with an OS 120 4 stroke but I know nothing about 4 strokes. Are they more trouble than 2 strokes? What about valve adjustments and such? I'd hate to have to send the thing back to the factory everytime I have a problem. (My other option for this plane is the OS 91 2 stroke)

RE: What To Expect From A 4-Stroke
 

It is best to tune a 4 stroke with a tachometer; the variation in pitch from lean to rich is not as noticeable as a 2 stroke (I've not yet fired up my first four stroke, but did work with my trainer on his and got a little experience).

Read the instruction manual. If any adjustments need to be made, they are not difficult, and the engine comes with a gauge and the tools to do the adjustments. OS four strokes have the reputation of being very easy to run, and running right out of the box. I wish I had one (in the Super Stearman I don't yet have).

I say get the four stroke, and in the mean time download the manual and read it a few times.

I love OS engines and really can not wait until (they come out with a 1.50 four stroke and) I have one.

RE: What To Expect From A 4-Stroke
 

if you bought a brand new engine....you shouldnt have to mess with anything other than the carb like you would on a 2 stroke the valve lash should be fine factory,,,, the key IMO opinion to get that put put put put idle , is to set the low end right on....to rich and will idle rough, too lean and the idle will fade, and die when you try to throttle up

RE: What To Expect From A 4-Stroke
 

Good advise so far. I'm a 4 stroke nut. Currently have 11 of them. I'm trying to get a trainer ready to loan to one of our guys and it has a 2 strokd 40 one it. None of my four strokes have been as difficult to tune as this 2 stoke is. It is just tempermental.

I've been flying the four strokes for almost four years now. I've checked the valve lash on a couple, but have yet to have to adjust one other than the Saito 45 I rebuilt. Reasonable good fuel and glow plug and a proper tuned carb and it's like jumping in your car. Hit that starter and away you go.

Don

RE: What To Expect From A 4-Stroke
 

You'll love the 4-strokes. The mixture adjustment is no different that a 2-stroke other than it can a little more difficult to set "by ear". Once it is set you will likely never have to touch it unless there is a big temperature change. Best part is the great sound though.

Many people claim that you need really high nitro content fuel but I run 15% Cool Power in all of mine and they run great.

I've also never found tight valves on one yet but if you have a basic understanding of engines whether it is from working on cars, bikes, mowers or whatever, you'll have no trouble maintaining an RC 4-stroke.

RE: What To Expect From A 4-Stroke
 

Two words - B. S.

It is never a good idea to tune an engine with a tach.

4-strokes are no more difficult than a 2-stroke, but there are two rules:

1) you MUST use a 4-stroke glow plug.
2) they run better with 10 - 15% nitro.

Aside from those two things, they are just like a 2-stroke. Get one, you'll love it!

PS, as far as adjusting the valves goes, I have been using 4-strokes almost exclusively for about 20 years and have needed to adjust valves once

RE: What To Expect From A 4-Stroke
 

That's really great advice, Mike, until someone takes it and sends a 16 or 17 inch prop flying across the pits because they got too lean. Good grief, man.

Most people simply cannot tune a 4-stroke by ear. Some of you guys have a problem with that for whatever reason, and can't seem to accept it. Why? You're not helping anyone by doing that.

RE: What To Expect From A 4-Stroke
 

I thought that you tuned with a tach to find the highest rpm and then richened until the rpm backed off a few hundred rpm's. Have I been tuning my Saito 62 wrong? Just curious why you say it is never good to do it that way when it seems to me like just a different way of doing it.

I am not trying to start an argument or anything, just curious as to the reasoning behind your statement of it is never good to tune with a tach.

RE: What To Expect From A 4-Stroke
 

I've got lousey hearing, but even I can hear when the RPM start to drop.

What I HAVE seen is people throwing a prop because they are trying to hit 11,000 RPM with a 4-stroke, OR the 16,000 RPM their manual says their 2-stroke has it's highest horsepower at.

Allfat, the way you are doing it is correct, but too many people use a tach to hit a "Target" number - which is NOT a good thing to do.

RE: What To Expect From A 4-Stroke
 

Well, sort of.........

I use a tach with my 4 strokes to make sure I'm NOT exceeding a "target" number with any given size prop. However, once you become familiar with your engine/prop/fuel/plane setup then the continued regular use of the tach will not be necessary. Most 4 strokes are the "set & forget" type of contraptions [8D]

RE: What To Expect From A 4-Stroke
 

I've never used a tach on any of my engines, and never had a problem with power. Save your money.

NorfolkSouthern

RE: What To Expect From A 4-Stroke
 

I've got a tach (for experimenting with fuel mixtures, prop sizes etc) and I've never even thought of using it to tune my 4 stroke 1.20 ASP, nor do I have any idea why anyone would need or want to. If you can tune a 2 stroke by ear you can do a 4 stroke too, and trying to tune an engine to get the last n'th degree of revs out of it is asking for a dead engine. Peak the revs out by ear (surely you can tell when an engine's getting faster or slower by the sound?) then back it off a few clicks, make sure it's running smooth, then leave it alone and you'll have a reliable, strong engine that'll run for years. Remember, if it aint broke, don't fix it!

As for valve lash the only time I've had to adjust mine was when I pulled the engine down to check for a bent crank after a somewhat vertical "landing", however from having worked on old cars for years I can tell you that it's worth taking ten minutes to look at the valves once every twelve months or so, just to stay within tolerances. It's a very simple job that won't even need the cowl on your plane removed (except for the few planes where the engine's completely encased), and it'll make you feel like a real mechanic and impress the pants off your friends at the club who only own 2 strokes when you casually mention "oh I checked the valve lash the other day, it was a few thousandths of an inch out so I tweaked it - runs great now". :D

Oh and before someone talks you into buying OS because they're "better", my ASP cheapie 4 stroke runs as well as any OS one I've seen, costs half the price, and is tuned exactly the same way (it is after all a direct copy of an older OS engine). Magnum engines are also great value and are identical to ASP's.

RE: What To Expect From A 4-Stroke
 

For the vast majority of us that is simply not easy to do. If I can accept that you're special enough to be able to do it, why can't you accept that most of us aren't?

RE: What To Expect From A 4-Stroke
 

Err.. maybe coz most of the people I know can tell the difference between a rising pitch and a falling one? We've got 230 members at my club and I've never seen anyone use a tacho to tune any engine... glow, diesel, or gas. That being said, if you need a tacho to tell you if it's getting faster or slower then go for it but I think it's you who's not doing people any favours by making tuning an engine seem harder than it is. I really don't mean to offend you in any way but it's just not difficult, you just turn the knobby thing in till the engine noises starts getting lower instead of higher then turn it out a little bit. It's not rocket science...

RE: What To Expect From A 4-Stroke
 

A club of 230 special people, eh?

You're right, it's not rocket science. Pretending that using a tach is hard to do certainly doesn't do anyone any favors. Perhaps you haven't used one? You simply hold it behind the prop, tune to the peak RPM, and then drop it 300-500rpm. It's simple, precise, and very safe.

Why some of you become almost militant about this baffles me.

RE: What To Expect From A 4-Stroke
 

I only get upset about it when people insist that using a tach is a MUST for tuning a 4-stroke.

Using a tach is a great way to tune an engine (2 or 4-stroke) IF it is used properly. But too often it is not used properly, and just as often, the person using it could do it just as easily by ear.

For those who say, "You need a tach to tune a 4-stroke", I say, "Then you had better use it on your 2-strokes as well"

If you can tune a 2-stroke by ear, then there is no reason why you couldn't tune a 4-stroke by ear.

RE: What To Expect From A 4-Stroke
 

I am using OS Saito and YS fourstrokes. They all seem to be a set and forget when it comes to tuning. The OS is the oldest with the most run time on it. I quit counting past 25 gals. It has required the most valve adjustments,but only 2 times a year. That takes just a few minutes and it very easy to do. It is still one of the most realiable though. It has a very low idel and has never deadsticked. Some of the the guys I fly with us OS 120's and the really run great. Once you start using 4 strokes you will really like the smooth power and performance of them. I havn't had a 2 stroke since I sold my trainer, and do not miss it.

RE: What To Expect From A 4-Stroke
 

So it would seem, if it were as difficult as you seem to think.


I never said using a tacho was hard... as you point out it is in fact quite easy, just unnecessary for tuning. If you read back to my original message I stated that I do indeed have a tacho, and that I use it for things like comparing different propellers (in conjunction with a fish scale... RPM vs thrust) and different fuel blends.


I'm hardly being militant. As I said earlier if you want to use a tacho then go for it - it's absolutely no skin off my nose. If anything I'd describe myself as bemused at the thought that they're required for tuning and at your defensiveness about the whole topic but hey, do whatever floats your particular boat. The best thing about this hobby is there's so many different toys that we can all do whatever makes us happy.

RE: What To Expect From A 4-Stroke
 

What To Expect From A 4-Stroke .........

A lot less oil to wipe off your plane after a flight.

Can be more expensive to repair than a 2 stroke in case of a crash.

They sound a lot better than a 2 stroke.

RE: What To Expect From A 4-Stroke
 

Hi!
Four strokes are as easy to set by ear as any other engine. In pylon racing I think all seasoned pilots set their engines by ear! Have never seen one set their engine by a tach on the starting line.
A Tach is useful only when you file and modify a prop and want to compare to other props and try to reach a certain rpm.It's also good to have a tach when you want to set your engines on a twin to rew approximately the same (which isn't really necessary) before take-off.

If you haven't flown a four-stroke before... then for heavens sake try one out in another airplane before trying it in the Great Planes GEE-BEE R-2.
I have flown the GEE BEE R-2 now for 4 years and it is a very easy airplane to take off and fly....but, the landings are very, very demanding (that means difficult) to accomplish without flipping over.

Part of the problem is the high weight! Part is that the Great Plane GEE BEE R-2 wing is set +6 (stab 0) which means that on landing with a high angle off attack the wing stalls early (which means it will snap just before touch down).
The remedy is to build it light! a 20cc four-stoke is fine but not anything bigger (heavier). I have mine powered by a MVVS 15cc (.91) two-stroke with custom made silencer running a 15x4 APC and a Tettra 15oz "bubbleless" tank. All up weight is 5000g (around 11 pounds).

Before flying a plane like the GEE BEE R-2 it is good to try out several other fast flying/aerobatic airplanes so that you are used to what happens with high performance airplanes (Why not flying Q-500 racing). Other wise the first flight of the GEE BEE will not end so well...

RE: What To Expect From A 4-Stroke
 

What to expect from a 4 stroke.............like everything else in this hobby, expect difference of opinion! Gotta love it.

RE: What To Expect From A 4-Stroke
 

Dgremlin


Once you have a 4 stroke, that's all you are
going to want to fly.


I love my Saito 82 and I used a Tach during
breakin. This is my first 4 S. and compared
to a NIB K&B 61 from the 80's i'm trying to
breakin, it's by far much better technology.

Bob

RE: What To Expect From A 4-Stroke
 

Try explaining that to my ears. Are you an MD now, Mike? Or have you decided to bolster your opinion by means of exaggeration?

RE: What To Expect From A 4-Stroke
 

Very true. Well, true until you try a good running gas engine.

RE: What To Expect From A 4-Stroke
 

Chuck,


A 4 stroke Gas is on my Wish list :D


Bob