4 stroke longevity

[Russell Shaffer]

How does a four stroke engine's life compare to the old standbys?  I like the idea of quiet fuel economy, but do they hold up as well as a two stroke?  There are sure a lot of very small moving parts.

[proparc]

Russ,
It's a wash. A high quality 4 stroke will last as long as a high quality 2 stroke. I have both.

A super high quality 4 stroke like a Saito will propably last as long if not longer than a PA.

A crap 4 stroke like a Magnum will probably last as long as a Chinese version ST 51.

All this is assuming you know what you're doing.

[Dennis Moritz]

Sorry to disagree. But I have seen three or four Saitos blow up in the last two seasons. Two 72s. One with a bent rod, one with a broken valve train, including a destroyed pinion drive gear for the valve train. One Saito 40 was sent back for a rebuild and returned not usable. The owner insisted on receiving a new engine. These engines were owned and used by modelers with lots of experience and ability. Winning stunt flyers. The Saitos 72s were in competition planes. One failling after half a season of competition, one failling earlier. The 40s were used as sport engines. In general the four strokes have received a pass. Difficulties and faillures in their operation are not usually reported. Even though some four stroke advocates are aware that problems have occurred. Also, I have seen less experienced flyers break in their engines and achieve less than reliable results. Usually choosing to go a different route.

[Bob Reeves]

Be interesting to know what prop and RPM the ones that had trouble were running. My Saito 40 is chugging along at 8200 with an 11-7 and I'm betting it will run as long as anything on the market.

[Dennis Moritz]

Yes, there was mention on SSW of the rpm max out issue of something like 8500 rpm with the Saito 72 when I brought up  the problems I've seen with Saito engines. Seems to me, if these engines need to be maxed out at 8500 rpm or so in order to insure their durability, various advocates of four stroke engines need to be specific about this limit. In the past they have not. The flyer who is continuing to run a Saito 72 in his top 20 stunt plane, despite the valve train/pinion faillure, believes the problem may have been with the oil content in the Omega fuel and/or the very tight ring fit of his particularly well broken in engine. Very little oil was seen flowing from the crankcase vent tube, indicating piston blow bye may not have been sufficient to lubricate the pinion gear. The Omega fuel was recommended by an experienced RC flyer familiar with 4 strokes. But all this is theory. His rebuilt engine is now being fueled with Powermaster (at least that was so a few weeks ago), it shows a good amount of oil exiting the vent. Similar to another rebuilt Saito 72 lent to him in the interim, when his engine was off for repair. Again, if there needs to be sufficient blow bye, or in other words, if the ring/cylinder/piston fit needs to be somewhat loose, this should be talked about as well. The power characteristics in the plane I'm talking about is good. No issue there.

[Bob Zambelli]

I’d like to chime in here also. I probably have more time on various 4S engines than anyone here as I’ve been using them for around ten years. From the little OS .20 up to the SAITO .91.
I have never had a failure in any 4S engine – EVER.
Two issues that I will address, however:
I have had to replaces bearings and a valve on one Surpass .40 that I bought used with zero knowledge of how it was run in. The bearings did not fail but were somewhat noisy. The valve was part of a bad batch that, according to the place I bought them, came through on some 40s and 48s.
Also, I bought a new SAITO .30 that had a problem with the cam/valve interface. I sent it back and it was rebuilt but not to my liking, as the valve clearance would not hold and the black discharge got darker instead of lighter. I returned it, requesting a NEW engine and they complied. That engine now resides in my Argus and is as close to perfect as I could ever want.
One thing that I have always recommended regarding lube: NEVER go below 22% total. My friends in Italy, who fly 4S almost exclusively, warned me about lubrication many years ago. When I use the YS 20/20 (all synthetic), I add castor to bring the total up to 23%.
I can truthfully say that I have never had a lubrication related problem on an engine after it was properly broken in (The SAITO .30 was a fluke. I have four of them and have only experienced the problem with the one).
I was recently translating a document from French to English and I read about fellows over there with well over 900 flights with zero maintenance. All my engines, by the way, have not required valve adjustments after initial break in. I usually check the play once a season. And, I have never burned out a plug.
Finally, I should add that, in general, I do not go below a 6” pitch. I have experimented with 4.5 and 5 but the engines seem happiest with 6 or 7. My Surpass .40 now turns an 11 ½-6 ½ and works very well. They just like to be loaded down.
My OS 40 4S turns a Top Flite wooden 10-6 and a Master plastic 11-7 at the same speed but the airplane barely moves with the 10-6.

Bob Z.

[Dennis Moritz]

Bob, of course you are aware of the experiences I am talking about with the Saito 72s. They happened to members of our club. As far as I know this is the first public mention in a USA forum of lubrication issues with the Saito, requiring 22% or 23% lube. Similar to your experience with the Saito 30, one of the Saito 72s required further replacement of parts when the engine came back from the Saito designated repair agent. To recap, some now recommend an 8500 rpm ceiling and Bob is now talking about 22% to 23% lubrication. I don't think our club member who flies a 72 in competition knew about either caution going into this season.

[Bob Zambelli]

Hi, DM. Yes, I know about the failures in ours friend's engines but I had no idea what oil content was being used - all I remember is color.

Consider this: I NEVER volunteer information about 4S engines at the flying field.

Why? I did it once a while back (lubricant ratio, in fact) at a contest and I was told "mind your own f****** business, I know what I'm doing". The person was nobody that you know but it set me to thinking - it really wasn't any of my business. After that, I made no comment no matter what I saw people putting in their tanks.

However, if someone ASKS my opinion about lubricant, I will gladly volunteer information, to be taken simply based on my experience. The final decision is, of course, theirs.

And, of course, I will ask you: "Have you ever seen one of my 4S engines fail?"

Bob Z.

[Dennis Moritz]

Yep. Some had difficult days at our field.

But the larger issue is the unqualified endorsement these 4 stroke engines are given by some advocates. Despite their knowledge of faillures and shortcomings. If these engines need to be run at a certain lube ratio and bellow a certain rpm and have sufficient blow bye (?) to insure long term reliability it seems to me the gentlemanly (and responsible) thing to do is tell fellow modelers about this. We give all kinds of advice about running foxes, fps, LAs, thunderchickens et al. Richard Oliver is even insistent about telling customers exactly how to break in Rojett engines, fuel to run and so forth. I'm sure Randy is equally scrupulous. Like I said some give four strokes a pass. Counterproductive. Not useful here.

[phil c]

When in doubt, read the directions.  OS recommends 20% castor oil, minimum.  The manual for my Saito 91 recommends 20% lubricants in a high quality fuel.  A few percent more sure wouldn't be a bad idea, considering how much harder CL engines are run than the typcial RC use.  Both mfg'ers recommend around 11,000 rpm for the upper limit, but when you put the recommended props on a reasonable size plane 9-10,000 is much more realistic.

Dennis is right.  If folks have had problems and had better luck with something like an 8500 or 9000 rpm limit it would be good to pass the word along, like a lot of people recommend Y&S 20/20 fuel.

[proparc]

Four stroke motors are NO different than any other motor. Either you know you are doing, or you don't!! I've seen a guy fry a perfectly good Supertigre 46.  

In any event we, (control line flyers) really don't have the last say on 4 strokes. It's the RC boys that are the real authority on these motors.  They buy thousands of these motors every year and we buy DUH - six!!

Right off the bat, the 4 strokes are RC engines.  Most control line flyers simply can't get it together with RC motors of any type.  When I first came back into the hobby, I returned by way of RC.  That put me in good stead to tackle the 4 strokes.  For me, the Saito's are simply RC motors with valves on top.  NO BIG DEAL.

You don't need a four stroke to win in stunt.  You purchase these motors because, just like the RC boys, you like them.  I buy Saito's because I work hard for my dollar and I am not aware of a better value in terms of quality/price on ANY engine 2 or 4 stroke.

If you can't get it together with 4 strokes then, leave them alone.  Given the volume of purchases that control line flyers make on four strokes, Gen Saito is not going to lose any sleep - trust me!!

[Alan Hahn]

Phil,
At least in my OS52S manual, OS recommends 20% oil. This includes 100% Castor but also synthetic as long as it is at least 20% total. As I recall, Saito is similar (~20% oil) , but the latest version I have seen (year 2000) of the manual (it seems to evolve over time!) says not to use 100% castor.

My take on the longevity is that if you are breaking crankshafts, I am thinking the prop used is too big. If you are swallowing valves, the prop is too small of a load and the  engine is reving too high.

[Dennis Moritz]

The top 20 flyer I refer to spent three years building his plane  a beautiful work, mentioned frequently in the mags. His Saito 72 failled after around 100 flights. His skill saving the plane, no easy feat. Didn't faze him though. Nor does he condemn the engine. Still working with a Saito 72, figuring out how to make it work and live long. A necessity in a dedicated stunt comp aircraft. Since you fly a lot of practise and need a durable engine that has a consistent engine run. This is in fact the third Saito 72 faillure we know about in our circle of flyers. I was reminded last night that another flyer friend had a Saito 72 let go. All of these engines were used by widely experienced expert stunt flyers. In fact the last gentleman is responsible for the design of a number of production model airplane engines.

The Saito 72s were all run with recommended fuels. Perhaps uping to more oil is one factor to assist longevity. RC engines are run differently than typical controline engines. Sure. No throttle shift for one thing during the flight. Also running an engine as a sport/stunt powerplant differs a great deal from serious competition use. A sport/stunt engine, one used occasionally in lower level competition is not stressed as hard as an engine expected to fly hundreds of practise flights with a consistent reliable run.

My interest is to be realistic about the characteristics of these engines. Also, if they need special care to keep them from blowing up, what is that care.

[Bob Reeves]

This info is right on Saito's web site..

http://saito-engines.info/prop_sizes.html

Says to limit the RPM to around 9500

[Dennis Moritz]

I'm certain the rpm was bellow 10,000. Put a tack on the 72 a few weeks ago, got something like 9300. On the upper limit perhaps. But in the acceptable range. Perhaps engine needs to run somewhat slower. Often a 13x6 prop was used. Is there a fuel specification? didn't see one.

[Alan Hahn]

Like I say, the info tends to morph over time. In my Saito manual from 2000 (downloaded originally from the web), the Saito 4 strokes are listed as having operational rpms from 12k (30 size) to 11,500 for the 72 size. I have no doubt the latest manuals might be different. And I expect they may change again in the future.

[Dennis Moritz]

Thanks to all, I'll pass on the information.

[Richard Grogan]

Russ,
It's a wash. A high quality 4 stroke will last as long as a high quality 2 stroke. I have both.

A super high quality 4 stroke like a Saito will propably last as long if not longer than a PA.

A crap 4 stroke like a Magnum will probably last as long as a Chinese version ST 51.

All this is assuming you know what you're doing.

Milton,
If I may ask, what do you mean by the comment "crap 4 stroke like a magnum"? I know several folks who fly with them without issues.. Its not a "pretty boy" like a Saito, but they're happy with its performance, I've even considered getting one myself. Good bang for the buck...
 If I were going to get a high dollar, larger 4-stroke, I would probably end up with a YS. The Saitos are very pretty engines though...
RG

[phil c]

One thing to keep in mind here, in my experience 4 strokes can be very hard to needle, especially solely by ear, and they tend to be much touchier on the setting.  An RC engine can easily be throttled back and landed any time you have a problem.  The CL 4 stroke is usually in the air for 5-7 min, which is a long time if the setting is wrong.

The 4 strokes I've run will struggle along just a bit rich, or just a bit lean, and often sound exactly the same.  If you happen to get it set a tad too lean, or it leans out as it unloads after takeoff it can get overheated pretty quickly.  Since it doesn't sound way off you may fly the whole pattern hot and lean, thinking its a bit rich.  And the lean run may not cook the motor the way a Fox 35 will do when it burns down, but it likely can still do a lot of damage, especially if the motor is only leaning out for a couple minutes in the middle of every flight.

Another problem seems to be props.  Figuring out how to match the prop to a specific engine and plane seems to be touchier than with 2 strokes.  On one OS 26 Surpass we went through something like 8 different props, including several different brands of 9/6''s.  The right prop(one 9/6) ran head and shoulders above the others.  On the best prop we had all of three clicks of needle valve adjustment, vs. less than 1 on the others, it held the setting all the way through the tank, and it didn't sag in maneuvers.  2 strokes usually aren't that critical.

Cooling in a cowled engine can mess things up severely too.  If the engine isn't cooled evenly different parts will get hot at different times during the flight, putting a lot of needless wear on different areas.