OS FT-160 Gemini, how much oil is required?
 

In the manual of my newly acquired OS FT-160 Gemini (twin needle carb) it is stated that:

"The FT-160 should be operated on a methanol based fuel containing not less than 18 % (volumetric) castor oil,
or a top quality synthetic lubricant (or a mixture of both), plus a small percentage (5%-20%) of nitromethane
for improved flexibility and power".

Interestingly, in the older version of the FT-160 Gemini (air bleed carb) manual one can read that:

"The Gemini Series engine runs on standard commercially available model glowplug engine fuel. Fuels containing
castor-oil and/or synthetic lubricants are acceptable but, for the best performance and reliability, a fuel containing
5—15% nitromethane is recommended. For consistent performance and long life of the engine,
it is advisable to use good quality fuel containing AT LEAST 10% lubricant."

Both manuals have been published by O.S. Engines Mfg. Co. in the years 2000 and 2004 respectively.

Why has the recommended oil content been increased from "at least 10%" to "not less than 18%"?
Is it because the engine really need that much oil to prevent premature wear, or is it simply because OS has decided to
play it safe in order to prevent engine damage caused by people tuning their engines too lean?

Regards, Red B.

RE: OS FT-160 Gemini, how much oil is required?
 

Original 4 stroke propaganda was about low oil and low noise. If you dont push the engine and put it on an old timer type plane you could get away with it. When people wanted performance, everyone reversed the opinion of oil. It might be a 4 stroke but the crankcase parts are pretty much the same as any 2 stoke so they need the same amount of lube to protect them as a 2 stroke.

RE: OS FT-160 Gemini, how much oil is required?
 

You are probably right.
However I have heard rumours about poor lubrication of the conrod bearing surfaces. If so, it would be interesting to know how people have gone about solving that problem (if it exists).

RE: OS FT-160 Gemini, how much oil is required?
 

I would bet most who have problems use too small or too large of a prop; spinning too fast or lugging the engine.

RE: OS FT-160 Gemini, how much oil is required?
 

Byron or Power Master 20/20 in my twin, 3 cylinder and YS engines! Castor oil in 2 strokes full synthetic (not blends) in 4's

I never run my engine dry, I have had one dead stick and the retrieval boat is helping others :D

RE: OS FT-160 Gemini, how much oil is required?
 

Older manuals suggested 14% for the smaller four strokes and 10% for many of the larger engines. IMO most of the time the lower oil works because the crankcase fills up with oil to about the level of the vent. But I suppose they had enough returns with apparent lubrication damage to rewrite their manuals.

RE: OS FT-160 Gemini, how much oil is required?
 

yes . i have the same problem .
realy how much oil is equired . ???? with more nitro need mor oil ???/

RE: OS FT-160 Gemini, how much oil is required?
 

Does anyone know what the gear ratio between the motor shaft and the propeller is on the OS 160 FT?

RE: OS FT-160 Gemini, how much oil is required?
 

The 10% probably works fine if you aren't stressing the engine too much (for example run WOT for the entire plane flight, but actually throttle back and use the throttle a lot). But you need to oil the cam area and oil the top end from time to time too. Oil can only get into the cam area and rocker box area as a vapor coming in from the crankcase past the bearings into the cam area and through the valve guides as blow by. So if you regularly oil the cam area, lifters etc and oil the top end then the 10% oil percentage in the fuel would work out OK. 

As a engine's displacement increases the amount of oil needed decreases. So a tiny .01 to .020 engine may need 33% oil to run OK, but a huge 1.80 engine may only need 8% to 10% oil to run OK. Other engines in between use a appropriate amount of oil accordingly.Now then a twin cylinder engine has two smaller cylinders so I think one needs to treat each cylinder individually to determine a good oil percentage to use. So it is like two .80 engines, thus something like 12% to 14% would likely be the way to go for oil percentage in the fuel.

When the four stroke engines first came out the different engine companies did state that they needed less oil. But with many people using the engines, then problems started occurring, and the manufacturers then changed their minds on it and started suggesting more oil of course.

RE: OS FT-160 Gemini, how much oil is required?
 

it s 1:2 ratio .

RE: OS FT-160 Gemini, how much oil is required?
 

Thanks npirzamani!

RE: OS FT-160 Gemini, how much oil is required?
 

npirzamani: I recently got a response from OS Engines and their reply to my question was that this engine had a 1:1 ratio. Can I find out how you arrived at 2:1 ratio?

RE: OS FT-160 Gemini, how much oil is required?
 

Camshafts for a four stroke engine are always operated at a 2:1 ratio. the camshaft spins at 1/2 the speed of the crankshaft. Otherwise you cannot get the four stroke action to occur with a intake and a exhaust stroke with the engine.
I do not remember ever seeing a four stroke engine design with a 1:1 cam setup, I can't visualize how it would work that way either.

RE: OS FT-160 Gemini, how much oil is required?
 

2 to 1 because the cam turns once per 2 piston full cycles. That why it s a 4 cycle; it takes piston 1 down intake, 2 up compression, 3 down spark/ power, 4 up exhaust to make one power pulse. Note Except Saito radials, radial cams are 4 to 1; 2 peaks per lobe. Still 2 to 1; cam just gets used twice, before it makes it around.

RE: OS FT-160 Gemini, how much oil is required?
 

<font size="2" color="#00265e">fiifiward</font> .
hi.
I ithink you mean cam shaft ratio and crank shaft. you are right .sory.

RE: OS FT-160 Gemini, how much oil is required?
 

i use 16% castor oil and reman pure methanol with  0% nitro . but i wwant to try lower oil 14%.

i think it s beter and cooler.

RE: OS FT-160 Gemini, how much oil is required?
 

On my OS FT-160, I get about 7400rpm at full power swinging a three blade 16 x 8. Is this typical of the OS FT-160? See on-board video taken during the third flight.

http://www.youtube.com/watch?v=sG9Af...WIjMQ_K8S6ct0G

RE: OS FT-160 Gemini, how much oil is required?
 

You have a pretty good hotrod of a 1.60. Mine swung a 16X8 APC two blade at 8500-9000 depending on weather. I ran 20% nitro and 20% oil in mine.

RE: OS FT-160 Gemini, how much oil is required?
 

Thanks JeffH :D. I run 15% Nitro with a mixture of 18% oil. Maybe that could be the difference...
Question I have for anyone on here. What other mixture is included in our glow fuels if they have 15% nitro and 18% Oil? What does the remaining percentage comprise of?

RE: OS FT-160 Gemini, how much oil is required?
 

IMO it isn't the stress that determines if 10% will be enought oil, but the areobatics and engine orentation. For example if the engine is mounted straight up and down then the oil and fuel that gets past the rings will fill up the crankcase to the level of the vent the fuel will quickly evaporate leaving mostly oil. Now if it isn't straight up and down but sideway's or inverted then the vent is in a different position. It may be higher or lower depending whre the vent is. On some engines the vent is on the backplate and somtimes not near the center. It may be that the oil level will be much lower, in this case then 10% oil may not be enough. If you are doing a lot of aerobatics then some manuvers, especially those that have a lot of zero G will cause the oil to sling out the vent no matter where the vent is. In those cases then you may need much more than 10% oil.

RE: OS FT-160 Gemini, how much oil is required?
 

What other mixture is included in our glow fuels if they have 15% nitro and 18% Oil? What does the remaining percentage comprise of?

Mostly methanol, but there may also be propolyne oxide for easier starting (especially in cold weather and especially on high nitro mix's), acetone for detonation, corrosion prevention additives, and maybe a secret ingredient or two.

RE: OS FT-160 Gemini, how much oil is required?
 

but may 18 % oil or 20%  is too much and the ring under stress...

RE: OS FT-160 Gemini, how much oil is required?
 

G'day Sport Pilot,

I don't believe the position of the breather would affect the oil percentage required by the engine. I've never noticed engines filling up to the level of the vent anyway. Every time I open one up there's just a few mls of oil in the crankcase.

The oil enters the the crankcase past the ring as a vapour or mist, any oil already in the crankcase would be beaten into a mist by the con rod and crank counter balance rotating at 10000 rpm or so. There would be liquid oil coating the surfaces and the crankcase filled with an oily vapour. After shutdown this vapour coalesces into the small amount of oil typically found.

Everyone,

I remember reading a column in one of the magazines that explained why larger engine require less oil (I think it was Clarence Lee). I can't recall exactly how it went but was something to do with the square and cube laws (if you double the length of something it's area will be four times as big and the volume eight times). So compared to a .10 an .80 which has eight times the volume only has four times the bearing area. Given that the larger engine will flow a lot more fuel the oil percentage can be reduced and still have adequate lubrication. Or something like that.

I think Earl is dead right though when he says the twin should be treated as two smaller engines, ie the oil needs to be kept up a bit.

Dave H

RE: OS FT-160 Gemini, how much oil is required?
 

Actually this is true to some extent. The crank is swirling the oil around and much of it goes out the vent, but it will build up at low speed and long low power or idle runs. I have observedatablespoonfull or two in the crankcase on a day where I was doing a lot of touch and go's with long approach's. In truth I was oversimplefying this. But the fuller the crankcase the more oil that will go out the vent and orientation is a factor.

The oil enters as raw fuel past the ring, the beating of the fuel oil evaporates the fuel which goes out the vent more easily. If you watch an idleing engine you will not see much oil go out the vent, but sometimes after it has been idleing for some time you will see slugs of oil go slowly out the vent. Trottle up an you will see the oil more in small drops traveling faster down the vent tube.

I am sure if you had glass backplate you would see the oil collecting with the crankpin and conrod bottom swirling it around. As itswirls some ofthe oil will dropback down andflow to the other sidewhen itis pushed back down and around, some goes to the front bearings and some goes out the vent. Butwhen you throttle up it would foam and be all over the crankcase, or more so. Either way the more fuel and oil that fills up the crankcase the more that goes out the vent.

I did not go into the wetted area. That may have been another discussion.

RE: OS FT-160 Gemini, how much oil is required?
 

Hi Sport,

I still think its mostly just oil that gets past the ring. The oil is deposited on the cylinder wall during intake and combustion while any fuel evaporates or is burnt of the cylinder wall during the same two strokes. The oil gets past the ring mostly during the exhaust stroke when the ring seal is less, and is scraped off during the intake stroke. At least that's my understanding based on my own knowledge and the writings of various engine experts, I could be wrong though.

I agree there's less oil coming out the vent during idle but there's less coming in as we'll, lower throttle setting so less mixture and lower RPM. So oil build up? Maybe, but maybe not.

I guess there would be more liquid oil at idle but even 2500 RPM is going to whip up the oil fairly well.

Well it's kind of the subject of this thread really. I was putting the theory forward as a likely reason for the varying recommendations for oil percentages. You are right though this was aimed more at everyone else, I'll change my post.

I would have thought that if the position of the vent or the orientation made a difference then it would have been mentioned by one of the manufacturers. I'm not aware that any have done this?

Like I say this is just my understanding and I may be totally wrong.

Cheers

Dave H