I know there has been much discussion on both of these engines...BUT...my friend is adamant that a 4 stroke engine requires much more maintenance and care vs the 2 stroke. This persistence has caused me to shy away from the 4 strokes. Is there any truth to this?
Thanks,
Patrick

Not really.

A tach is needed/essential for the INITIAL setup and break in for a 4 stroke. I guess you could call this "MORE" care and maintenance.

About every 1 1/2 - 2 gallons of fuel (this WILL vary by engine) the valves should be adjusted to maintain optimum power. The fuel used is deceptive. A 70 size 4 stroke is ROUGHLY equal to a 46 - 53 2 stroke in power, but only uses ABOUT 2/3 (or less) the amount of fuel the 2 stroke will use.

I guess you could call adjusting the valves once in awhile "MORE" maintenance. As for normal care, I treat mine the same way as I do my 2 strokes - run the fuel out of the engine at the end of the day, and for storage over 60 days I put after run oil in it.

I have a Saito 72 and love the engine. Others at my field have the OS and Magnum 4 strokes and seem to like them also.

I don't think you would be disappointed in the power OR find the maintenance and care that much different than a 2 stroke. I do know you (and any neighbors) will definitely like the sound of the engine.

A tach should also be used in 2 stroke INITAL setup and break in.

Cheers,

I agree with Campy. Bought my first four stroke a couple of years ago and will probably never buy another two stroke. There's just no comparison, and the additional maintenance is pretty much bunk. Yes, every once in a great while you need to adjust the valves (I haven't had to adjust valves yet), but it's a simple task that can be done in a few minutes.

My four strokes require much less "tweaking" once tuned than any of my two strokes ever did, so you could just as easily say that they require less maintenance.
Dennis-

Is there a guide for using a tach with four strokes? For example...a .91 four stroke would be optimal running a such in such rpm?
Pat

I agree with DBCherry. The little time I spend on the valves is a lot less than retuning A 2C every time you fly. I have two .72s and go weeks at a time without resetting the needle.

Tuning a 4C with a tach is a snap. Just slowly lean it till it maxes out the rpm. Then richen it 300-400 RPM.

David

I agree with everyone here. I'll add that as a general rule you should prop the engine to stay below 10,000 rpm's and as mentioned above, richen the high end about 400 rpm's below peak. I have two Saitos and probably won't buy another 2-stroke either.

No but the occasional bent pushrod, bad bearings, etc is a lot more maintenance.

I wonder what two strokes you have tweaked? I have both and see no differance in the amount of tweaking, both are the same.

If the day ever comes that I NEED a tach to setup a 4-stroke (Or 2-stroke for that matter), I'll be deaf.

All you need is one ear (And most people have two!).

And a 4-stroke DOES NOT require much more maintenance than a 2-stroke. If your friend is ADAMANT about the fact that they do, then your friend (with all due respect) doesn't know much.

Why do people here beleive that a 4 stroke should run below 10K, yet the manufacturers (Saito and OS) all quote RPM ranges closer to 12K, lower for the bigger engines.

I find it somewhat arbitrary, and nobody ever gives a reason for the supposed 10K limit ???

ok, bad bearing.....that's any engine.........as for a bent pushrod......from what? Impact with terra firma should be the only thing that causes a bent pushrod. As for tweaking the needle, a two stroke is tuned almost everytime you go to the field. Adjusting valves is done once after breakin, just be sure to do it when the engine is cold. And I mean completely cold. If you do it warm it's wrong. After inital break in, the only time I even touch the needles on my Saito is if I change nitro content. They start everytime, and run great. I don't think I'll ever buy another two stroke. And yes you do need a tach for a 4 stroke, it is too hard to hear when you hit your max lean setting. If you go too far it'll backfire and kick the prop. The 2 stroke has it's purpose, aka pattern, as does the four stroke. Not let me cover my a** cause someone will jump it if I don't, what I'm meaining is that you don't see 4 strokes in pattern. If your plane doesn't beg for one type or the other, go with whichever one you want. Also, fourstrokes and quieter and cleaner than their counterparts.


Neo

As is a four stroke. The carburation is the same, they are very simple and don't have anything in them to compensate for temperature and pressure as our automobiles. I check them each time I go to the field and find absolutely no difference between two strokes and four strokes. Yes some difference in brands yes, two and four stroke no. A couple of my engines have almost the same carb on the two stroke and four stroke and I see no difference in how they act or how they tune. Now maybe you have a YS or Saito, I have no experiance with them or Magnum, and maybe they are better, I don't know. But if they are it has nothing to do with being a four stroke.

As for bad bearings, YS is the exception here, but the oil comes from blow by and then flows through the bearings before going out the crankcase vent. This means that any worn metal from the rings and sleeve must pass through the bearings. OS saw this as a problem and switched to sealed bearings because of it.

Thought YS was still fairly popular in pattern. Though the OS 1.4 electronic fuel injected engine is replacing a number of YS engines.

I guess the point that we all forgetting is THIS IS A HOBBY, which meas - there is no pre-set path for doing anything!!!! Some like building ARFs, some like build planes (trains, automobiles ) from sticks, some do not building part at all - they just like flying.

Some like 2 strokers, some like 4 strokers, somebody can fly a plane with the engine "OK tuned", and some are trying to "squeeze a last possible RPM" out of it .

Botom line is - find wht YOU like, build what YOU like, expirement and GO AN HAVE SOME FUN!!!!

It has something to do with valve train limitations. Some valves start to float above 10K rpm. However, the YS 63 runs the best between 10.5K - 11.5K rpm without fear of valve train failure.

I understand that valve float is an issue. However, the manufacturer has some control over that. An example is OS's Surpass 26 car engine. They document that it runs up to 17K: http://www.osengines.com/engines/osmg2092.html ... and part of the reason it runs at such a high speed is "Reinforced valve springs that reduce "floating" at high rpms ".

So, I am still left wondering, about the often repeated 10K number.

Jim:

Most of the Saito engines will run up to 15K or so before floating the valves.

The late FA-120S has springs that are much stronger than the earlier ones, as a guess you could run an old FA-120 over 16K using them.

But why bother? Torque peak on most is under 10K, hp peaks around 11K, so turning them higher gains nothing other than increased wear.

Bill.

Thanks Bill, I wouldn't expect to run them past their power peak, and that of course is a good reason to limit the speed.

But OS, for one at least, quote RPM's along side their power figures and they are 11 and 12K for most of their single cylinder Surpass engines. But, I still see the 10K number repeated here over and over and wonder if people are just repeating what they read or was if there is some well understood reason that I didn't "get".

The query is born out of experience with my own old Surpass 48 that I recently run at 11K and found it to be quite happy, with improved throttle response, and less rich low end. It has an airbleed carb - formerly I was running it just over 9K with the air bleed screw fully open and it was too rich. At 11K max, the mixture seems to even out over the entire throttle range.

Jim:

I think a lot of the 10K limit might well be parroting, and many of the 4s engines perk along happily at 11K-12K rpm. But if you have the power you need at a lower rpm, why go faster?

An engine has so many piston strokes in its life, at 12,000 rpm you're going to get there at least 20% faster than you will at 10,000 rpm.

A 2s engine has another advantage many over look; when it's running right the con rod is always in compression, a 4s con rod has to stop the piston's upward movement on the exhaust stroke, and pull it back down on the intake stroke. The 4s rod is constantly changing from a compression load to a tension load, this can lead to a fatigue failure much faster than in a 2s engine with its constant compression load. This loading goes up as the square of the rpm.

If your little OS runs better with a 12K peak, run it with a 12K peak. It will definitely wear faster, but you probably will never know it as it has a pretty good service life anyway. I'm just conservative, I've probably destroyed more engines than most people have owned. It has cost a fair amount of money, but it also has gotten me to the point where I can sound like I know what I'm talking about. And maybe I do, once in a while. Haw.

Bill.

I suppose since they are more complex, 4-strokes have the potential for requiring more maintenance. I haven't had to do much to my OS .48, FWIW. In fact, it hasn't run in probably over 4 years (I had "retired" it after I had some trouble with it running poorly, possibly had to do with my relative inexperience at that time), but tonight I tried it out after having the carb off to soak (throttle barrel was stuck....I hadn't used after-run oil or anything), and it started pretty easily! Ran ok too, still needs some tweaking (after I get a new prop for it, hehe) but I'm very pleasantly surprised with how well it runs after the trouble I had with it a few years back, and considering it's not been run in that amount of time.

I love the sound, and also the nice smoke trails 4-strokes produce.

-Matt Bailey

(edited for speeelinh errir.......)

to some extent. an engine lugged down with too large a prop is going to have a much shorter life (according to the total number of piston strokes) then a lighter loaded higher rpm engine.

Ryan:

You have a valid point, but I was talking about keeping the engine in a comfortable rpm range. Overloading isn't good for any mechanical device. Or for a horse, either.

Haw.

Bill.