The 90 FSR comes to mind. Very good engine, they should have kept it. I have a couple of them and no issues at all



[quote]ORIGINAL: William Robison

[b]OS used to build good engines. I have several older ones that still run perfectly.

That would be nice to get involved in that "secret stuff" I think my kid will be going that way when he finishes his "mech eng" degree next year.

i had similar problems with the OS 91fx,i bench ran it with the reccomended prop,ran about three tanks of 10% through it,tuned it by the specs,this is one of the newest versions.when i finally got the ring seated in,it started to run a lot better and kept getting better as i set the lower end.this engine was mounted in a VF edge540 and is cowled i have a cut out for the head.i have never had overheating problems and it runs good and decent power.i have had this engine for about a year now and am still using the stock glow plug that came with it on 10%cool power we buy in bulk.i am using a Pitt's style muffler the engine is mounted sideways.

sparky333, try a foremost pressure valve on your muff line. Good bandage on a notoriously poorly designed motor. Fuel delivery is the problem with them in my opinion, unless of course the stars and the moon are aligned perfectly, which I am HAPPY that some guys have that benefit. KELLDOG

On mine it initially overheated - dropped down to 5 percent fuel - it would kick back hard when hand starting so I put in a second head gasket and it is much better. The large volume Pitts muffler comes with reducers in the exhaust tubes which helped with fuel flow as well. Using 13x8 and 14x6 apc props for sport flying. If you dont like the remote needle valve the Magnum 91 xls carb can be used on it. Also using an OS8 plug. Mine is a strong and reliable engine.

thanks guys for all the input i am very greatful you to kelldog good advice i dont know what i am doing but its going back to os and im going to run another one i have on the bench that is broken in already the next one i will make sure i dont over prop and overheat it thanks guys

You know if you think about it, with the cost of a 91fx, you could get a G90 and a Pitss Muffler

All, Sparky


Could everyone have overlooked the ring end gap??

In ringed engines there is a size spec for this gap, so when the engine runs at its intended working temperature, it must be as closed as possible, but not closed!

Could it be too small and the ring ends be butting together, as the engine reaches operating temperature?
With this engine's steel sleeve, you may not be able to notice any unusual wear, but the engine will invariably overheat and die on you, for no apparent reason...

But no! It is not steel, but ABN. The base metal for the sleeve is brass and it is plated all around with nickel (see [link=http://www2.towerhobbies.com/cgi-bin/wti0001p?&I=LXCL08&P=Z]part specs[/link]).

It would not survive even for a minute, if butting occurred.
So we must think of something else...

You want your ringed engine with a steel liner? Get the 1.08FSR.

I think my 1.08 is ABN? I'll have to check the manual, but I think I read something about an "advanced coating" or something like that? Mine was made in '96 I believe...

Proptop,


I don't doubt what you are saying, but the [link=http://www2.towerhobbies.com/cgi-bin/wti0001p?&I=LXCL02&P=Z]Tower web page[/link] says otherwise.

I don't have one to make sure...

I had to go get the instructions to make sure myself!

It says..."This engine has a special low-friction, ultra hard-wearing, composite cylinder plating..."

Wonder just exactly what that means?

I thought it had a steel sleeve too, until I read the inst. sheet...

Someone here on RCU said that the early ones had a steel sleeve?

That would make sense...because I think the mid 90's was when things started getting (let's say ) less expensively made, at O.S.?

Edit: Another supposition... perhaps the latest ones have gone back to a steel sleeve, after all the peeling episodes with other engines?

Proptop,

One more thing: The ring is said to be steel too... but it is supposed to be a dissimilar metal, cast iron, most likely.
So they could all be wrong...

Don't know how that boner got in there and nobody here found it. The Marketing department must have been using a lot of "cut and paste" when they were writing tech notes for the FX-series of engines.

The O.S. Max .91 FX engine has a STEEL cylinder liner. The piston is aluminum and the ring is steel.

An ABL liner is not magnetic. The one in the .91 FX is strongly magnetic. We know this because we send out scrap metals for recycling, and use a magnet to separate the brass liners from the steel ones.

The MC9 plug is WAYYYYYYYY too cold for this engine. Enya 3, K&B-1L, K&B-4c, OS-F, OS-8 at the coldest.

Bill,


Get the handle on the Tower Hobbies affiliate.
It cannot print out incorrect info all over their tech pages.

Earlier it was the .91VR-DF engine, listed as 'actually' ABN (it has been corrected since) and now the .91FX...


I never held such a sleeve in my hand to examine, so all I can look at is the Tower tech pages.
I cannot look to the engine manufacturer, to see if the Tower tech page is not incorrect...

Is the .50SX sleeve ABN, as stated in Tower, or is it also steel, like the ringed .91FX?

As stated up above a ways, The ring cannot be steel and ride against a steel liner. The ring is CAST IRON


He a link to the Japanese site if anyone cares to go there.... You can get manuals, three views, and exploded views there.

http://www.os-engines.co.jp/english/...t/airindex.htm

Enjoy,

Jim

Tower Hobbies has over 50,000 different items (and more coming). They create tech notes for several thousand products each year. A few are going to get by them. We are the service center and cannot read all the notes they produce, even for our products.

OK. We'll get that double-checked. You're likely right. It's most certainly a ferrous product, since it's also very magnetic.

Thanks,

bax

Hey guys I had some problems with my OS91 FX. It cuts off in WOT. I have a pitts muffler. What I did was replace the fuel line pick up line with a bigger line and a bigger clunk. I also replace the fuel line from the tank to the needle housing with a bigger line and left the other line alone thats going to the carb. I use to plug one of the exhaust coming out of the muffler so I have enough back pressure to the fuel tank. Since I replace the fuel line that fixed my fuel starbation at WOT and I removed the plug on the exhaust port also and richen my needle valve. Right now I got 4 turns from fully close position on the needle velve and I'm running 15x7 APC. I tach it at around 9200 rpm. I'm happy with it.

This is a perfect example. If you need to do all that crap to get a 91 fx to run half way decent, that is a red flag. 4 turns out That idea works here at 5000ft but if your not, I am sure whatever problems your engine has are still their, just a bit masked.

It is easy to get frustrated and then lose faith in your own abilities. A reminder from friends can sometimes bring thoughts forward that lead to solutions.

I've had a couple of bad OS engines over the years. Engines with known problems, so I'm not one to say that it is impossible that the problem isn't the engine. Especially since Mr. Ogawa has passed on and the business is being run by others with an obviously different philosophy. However, occasionally OS restores my faith in their abilities by producing an engine such as the OS.46AX. I have heard nothing but praise for that engine.

Sometimes just the repeating of the litany of engine failure modes is enough to jog the mental processes into being productive. Some folks shouldn't be so sensitive when others are simply trying to help. Especially when said "others" are not familiar with the forum's inhabitants' skill level.

Ed Cregger

I currently run this engine on a super hots with a os#8 plug and a 14x6 apc with 10 %. I have had this engine for about 8 years ... pulled it out of the ground on many occasions..lol...and it still runs like a champ...my current combo of fuel, plug and prop are about the best I have used with this engine. Tuning this engine can also be a pain in the rear. Start by setting your low speed needle...first, open the high speed needle 10-15 clicks from closed just to allow fuel to enter the car..then play with the low speed adjust till' you get a good idle..then open the throttle to mid range and open or close the high speed needle 1 or 2 clicks at a time and give the engine enough time to catch up to the adjustment. Once you are running steady there, open up to full throttle..repeat...it should be close to perfect at this point...if the engine drops off and stops it's lean and the HS needle should be open a few clicks at a time until it runs smoothly through the throttle range...if it runs erratic and spews tons of oil out of the exhaust it's to rich and the HS needle should be closed a hair or 3. Keep in mind that this engine will lean out alot in the air so a slightly rich setting is ideal for optimum performance. This isn't necessarily typical tuning protocol, but it's the best method I have devised for my engine over the years. It's not a fast ordeal and best done at home, not the field...so you don't use your frequency for long periods while tuning when another guy on your frequency could be flying.

Maybe you just need to involve your engine in several crashes first and just skip normal break in procedures....it seems that after each crash mine runs better...lol

If pistonring was made of steel, it will be plated with chrome and the sleeve must be cast iron, mostly in automobile engines. When i replaced the steel ring then i tried to break the old steel ring, the ring was soft.. while the cast iron ring will break easy off..

Cast iron ring are best to run with sleeve of hard steel, cast iron or sleeve in other material with surface of chrome, nickel or nikasil.

In model engines can be between 0.0001 mm to 0.005 mm depent on bore size in model engines.

If you see the light though ring gap when the ring are in the upper part of sleeve, the ring are worned out. If difficult to see the light, all ok.

Jens Eirik

Jens,


The ring end gap for full size engines is 0.0065-0.0115 times the bore diameter.
This can be seen in [link=http://www.kb-silvolite.com/article.php?action=read&A_id=32]this Keith Black web page[/link].

Our methanol fuel engines that generally run at a lower temperature should have the gap set at bore X 0.0080, or smaller.

For a 27 mm bore of a typical 15 cc (.91) engine, this means a gap size of up to 0.216 mm is OK.


But I was talking of too small a gap, causing the ring ends to butt together, as the ring heats to operating temperature, causing increased ring friction, wear, overheating and possibly breakage.
If the ring gap is smaller than the bore X 0.0065, or 0.1755 mm, in the case of 'our' 27 mm bore engine, butting could happen.

All:

In two stroke engines the ideal ring gap is the one where the gap is all but closed at operating temperature, this gives us, naturally, the least compression leakage through the ring gap. But remember, this is running a two stroke engine.

Our model four stroke engines, with the exception of YS, control the oiling of the bottom end of the engine by changing the width of the ring gap. I'm "Stuck" on Saito, they are the ones I know best. The recommended gaps range from 0.127 mm in the 20 mm bore of the FA-30, up to 0.3 mm on the big 34 mm bore engines.

Bill.

tell the idiot that told you that to learn how to break in an engine and tune them. I haven't seen an engine yet built since 2000 by the major players, O.S. saito, magnum YS GSW and a few other that have mass produced dud engines. Tune it properly and it will pur like a kitten, that's of course if it wasn't ruined at break in.

Ajust the engine to peak RPM then back off about 3-4 clicks. you'll hear a slight drop in RPM. If it doesn't respond then the engine probably isn't fully brocken in. then set to idle. I use the pinch method. pintch the fuel line for a couple seconds and listen to the motor. if it speeds up and dies lean the idle out. if it just die richen the idle. if it maintains it's fine. advance to full and reset the high end, then recheck the low end. do this about 3 times, it should be a rock solid setting