Well, I am going to get my first four stroke engine and I have a few questions. I am going to put the four stroke in my 4*60 arf. I have only used two strokes so far, about 6 years or so. Right now I have the O.S.61 in it, but I think I need the sound of the four stroke now. I have use a few differant two strokes engines in the past from differant companys and I have found the O.S. if the best in my mind because they just run great with no problems. Question #1, is this the same with the O.S. four strokes.
I am looking at the four stroke O.S. FS-91 II Surpass and/or the O.S. FS-70II. With only a $40.00 price differance between the two I am ASSUMING I should go with the FS-91. Question #2, is this right.
Also I am going to ask about the Magnum XL-91 RFS, priced at $150 that sounds real good to me. I am just wondering if the Magnum will run as good as the O.S. I have never had a magnum engine so I don not know anything about them. I guess I am asking if any of you have both Magnums and O.S four stroke and if so which you like the best or are they the same. Thanks.

I have both OS and ASP/Magnum four strokes, though .30 size.
As far as price/quality/power, i find the ASP as good as the OS, even better if i'm permitted to say so. This engine hasn't failed me while the OS has for several times.

For your airplane, i suggest a .91 if you want similar flight characteristics as your .61 engine. Don't go the route of the FL-70, those engines seem to have a bad reputation.
If you do decide for the OS, check out the prices for the Saitos. They are lighter and have excellent qualities with the price being similar to OS's, being a good bet.

O.S. 4-strokes are generally regarded as being equally as reliable as their 2-stroke engines. Saito 4-stroke engines are very popular because they are powerful and very, very durable while also being very light weight. 4-stroke engines from other manufacturers like Thunder Tiger and Magnum also enjoy a following and generally have good reputations.

A .91 Four Stroke is a good fit for a Sig Four Star .60. As previously stated, a .70 4-stroke would be a bit underpowered, it would be like putting a .46 2-stroke on it. It would pull the plane around and be flyable, but it wouldn't be as much fun for aerbatics and such. An .80 to 1.00 4-stroke is probably the ideal range.

You've had good experiences with O.S. Max engines, and if you buy the FS-91 II Surpass for $249.99 you won't be disappointed. It's a strong, reliable engine that will give you many years of great flying service.

A Magnum, Thunder Tiger, or Saito .91 4-stroke would also give you many years of strong, reliable flying service. They're all very good engines, and with the Magnum on sale right now for $149.99, it must be really tempting to try another brand. I certainly can't talk you out of it, I own 3 O.S. engines and they've all been fantastic, but so have the Magnum engines I've flown.

Whether you want to stick with O.S. Max for quality, reliability, and best-in-class warranty service or try the Magnum and know you're getting a really good engine while saving $100.00 is a personal choice that only you can make.

Hello; I have a 4 star 60 with an OS 90 in it, it's the earlier OS 90 with the pushrods in the back. I think you'll find that you need quite a heavy engine to balance your 4 star. This is one reason to consider the OS 91 or Magnum91 over the lighter Saito. I put a Saito 100 in my 4 star 60 and found I needed a pound of weight to bring the c of g into line, so I looked aoround for the heaviest 90 size engine I could find.

I think you should look at Magnum, save yourself $100. My engine choice will be the lighter Saito's, because of the design. I have OS' entire surpass line, but I fly Saito. I have a surpass 91 I bought new but I have taken it off 4 planes now and replaced it with saito. If I need a heavy engine, I'll use OS. I find that more and more flyers are unhappy with the larger OS four strokes. I know that lots of people like them, but no one here.

Brooke,

First of all I would say congrats to you for buying 4 Stroke engine, I would call you lucky. I'm in love with O.S. 91 II Surpass, and Im planning to buy it, as honestly I have never used any O.S. engine not even 2 Stroke. I used ASP's .46 and that engine was so powerful, and screaming, it used to give me 40 to 50 feet vertical on my trainer. Now a days, Im going thru financial crisis, Im gonna get a job next week hopefully in standard chartered bank with it's head office in UK. Im also keeping in my mind Saito, cos they are the best proven 4 strokes, I've been flying for nearly 15 months.

I agree with Patxipt that ASP's engines are really cool, and Im gonna put 4 stroke on my 60 size similar like easy sport plane locally made. What bigedmustafa said, I really like that, I mean all three people gave so beautiful experiences and opinion which infact gave me much encouragement to buy 4 stroke engine either Saito, O.S., ASP or Magnum. China is really making good engines, ASP, Magnum, Thunder Tiger.

I would like your opinion about Super Tigre's 90 size engine which a friend of mine got used one for a very cheap price, and its Italian made, it can be used on 60 size plane? and how good it has a reputation?


Thanks and happy flying.

Mody

I found Super Tigers to have various problems where the other brands mentioned are much better, regardless of price. [8D]

a little off topic,but since its a 4st question, I have a used OS 91fs surpass a older one I have been having trouble finding a good idle with the mixture, I reset the mixture screw acording to the instructions, but can't seem to get a good idle out of it, any tricks out there I am missing,like clean the carb or something basic it seams to be running rich and gets good high end RPM's 10,200 but wants to stall at the low end it does smoke a bit but runs good just doesn't want to idle for me.should I check the valves I hate to run in circles for something simple I may be over looking.

Thanks for all your guys information. Just to let you know I did go with the O.S. FS-91 II Surpass. I guess because I have been hearing they are good engines and I already like the O.S. 2 strokes, so why not stay with O.S. for know anyway. I will let you all know how much, or maybe not, I like it once I get the chance to give it a try. For some reason I am thimking I will be selling some of my two strokes and replacing them with four strokes this summer. Or if I think about it why not just keep the two strokes in the planes I have now and just buy new planes to go with the other four strokes if I do get more, well that sounds better anyway. Anyway thanks guys.

You will enjoy the four strokes.
I took my Lucky Star trainer the other day to the field so my instructor would fly it to see if everything was fine.
There were two chaps there with 2 strokes planes, 46 size i believe, and a Magister.
The electric is electric, but when my trainer took off, you won't believe the wonderfull sound of a four stroke in the air, like a real airplane, but so so quiet! My ears hurt when the 2 strokes started flying, all that whining...
Good luck with your engine

Bigtim, check out the valve clearance, and then clean the carb and set the needles.

Bigtim:

Yes, definitely check the valve/rocker gap. Excessive gap can make the idle sloppy, I think the Saito gap is set about 0.010 inch. You can get tools especially for Saito engines with the correct wrenches & gap gage, don't know about OS but I imagine you can tools also. Also make sure you are using the correct fuel. Saito's love 20% nitro, but Magnums require less to prevent detonation (check Tower or the OS website for recommendations). Use a castor-containing fuel.

Be sure you use a good plug that is not too old. OS four-stroke plugs are awesome, just make sure you don't have any buildup on the coil. Also be sure there is enough air flow around the engine to prevent overheating. And finally, make sure the centerline of your tank is near or SLIGHTLY above the centerline of your carb. If the tank is low, the engine will have trouble sucking fuel at low RPM.

N

4 strokes are easy on the ears and hard on the wallet....

Glow Plugs for 4 strokes .... $7.49 each

Ear plugs for 2 strokes .......$1.00

I have 3 Saitos (82, 100, 125) and a recently acquired FS-OS91 II. The Saitos are great but I really love the OS because of its rock solid idle. After I broke in the OS, it's idle was very rough. I did a valve adjustment and it smoothed it right out. OS sells a valve adjustment kit for around $10.00. My OS keeps getting stronger the more I fly it and is currently my favorite engine.

that was the next thing on the list the valve adjustment, I went through the motor today to check for any loose screws needle valve assembly etc getting a new feeler gauge to check the valves should have done this when I got it my other OS 91's run great so it seemed a little odd that this one would run a bit rough being that it looks as though it was hardly run at all .

Hi!
The universal tank-placing-rule goes like this!
"The tank should always be placed so that the centerline of the tank goes tru the carb intake orifice ,or slightly Lower, when the airplane sits horizontal"

Eh? What'd you say? Some jerk who doesn't think four strokes need mufflers was reving his straight piped YS 1.20 in the pits while you were talking!

well here's a note for all you helpful people, thanks for the tips, after going through the engine I have had trouble with, I poped the rocker cover off and what do ya know the rocker arms were off a bit, the larger feeler gauge .010 slid through like a hot knife through butter unfortunitly when I went looking for a 5mm wrench I couldn't find one so I went ahead an ordered a valve adjustment kit for my OS, I have 4 so I figured I needed one anyway on thing about the 4 stroke if its out just a bit it will not run at its best, where a 2st is such a simple engine there is not that much to get out of adjustment, definatly for the beginner a 2st is much less of a hassle,seems like every time something gets out of wack I learn a new trick or how to solve a problem with the 4st, I don't even hardly touch my 2st and they run great.
not like I am giving up my 4st, there the perfect warbird engine for sure.

Hello bigtim; Here's a little tip, regarding your valve set. You can increase your valves stroke by reducing the valve clearance, also duration in increased. This tip is for Saito's; reduce your valve gap to .002, intake and exhaust, then re-tune it a bit rich, and be ready for a huge improvement. I don't know how well this will work on an OS, because I haven't personally tried it. I haven't seen any increased wear anywhere on the engiens I've done this to, as the barrel grows more then the connecting rod, valve clearances grow as an engine heats up. Try it!

Well, just letting you guys know I did get my O.S. 91 put in my 4*. I did have to do a little modifying, but nothing major since I did have it set up with my 2 stroke first. I just finished doing the break-in by O.S. instructions and ran the two tanks thru it. WENT PERFECT! It is great when you put a brand new engine on and it fires off as soon as you hit the starter. I am sure many other engine brands are just as good, but I have to say I love the O.S.
At the end of my second tank for break-in I set the needle valve to what I think I am going to like and when I would idle it all the way down it just sat their and would idle all day I think, but when I would shove it to full throttle it would rev up and not think anything about it. It also sounds like it would pull my truck off the ground. All I can say is that I am very happy with it and I know I will be buying more four strokes.

What prop are you using? After using a 14x6 Pro Zinger for break in, I settled on a Graupner 14x7 prop. The OS seemed to over rev in the air with the 14x6. On the recommendation of a fellow flyer, I tried the 14x7 and it has turned out to be a great combination.

brooke, scoreman. Try a 14x8 topflight with the OS91 Surpasse II on the Sig 4Star 50 ARF...

Skorman, I used the 13x6 to do the break-in and everything seemed real good to me. Now remember this is my first 4 stroke so I dont know if this will be the best fit or not right now, but I will play with it some once I start to fly it and check other props as well.

Fadi81, thanks for the information I will pick up a 14x8 today since I am going to a rc hobby show near me. It is not a huge show, but they have alot of stuff their that I can not live without.