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Jun 15, 2021, 08:08 AM
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Old O.S FS 1200 (Pre surplass)


Hello,

I have an old os fs 120 engine like in the picture.



The engine is complete and I don't really know what to do with it. I wanted to change to petrol, but I decided to renovate it and try to fly. I am looking for information about this engine, some suggestions and, above all, operating instructions. I can't find it on the internet. Thank you for your help.

greetings
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Jun 15, 2021, 01:21 PM
Still gassin' it.
Why not run THAT engine on petrol? It is extremely suitable for it.

Here's one I did for a friend of mine:

Voorlopige afstelling van Merlijn's oude 120 FS (4 min 29 sec)


As a reward, I got to fly the plane it went in, a 96" wingspan Fokker F VII

Fokker F7a flight (3 min 16 sec)
Jun 15, 2021, 01:28 PM
AMA 46133
SeismicCWave's Avatar
Quote:
Originally Posted by MarioSWD
Hello,

I have an old os fs 120 engine like in the picture.



The engine is complete and I don't really know what to do with it. I wanted to change to petrol, but I decided to renovate it and try to fly. I am looking for information about this engine, some suggestions and, above all, operating instructions. I can't find it on the internet. Thank you for your help.

greetings
This is really a perfect question for Bert to answer.
Jun 15, 2021, 02:06 PM
Registered User
JimboPilotFL's Avatar
Dave M will tell you about your engine.

https://search.aol.com/click/_ylt=A0...8RfpehPCZqNbk-
Jun 15, 2021, 02:30 PM
Still gassin' it.
Quote:
Originally Posted by SeismicCWave
This is really a perfect question for Bert to answer.
Given the use of the word "petrol", assuming he is either British or at least European, he can send it to me and I'll convert it for him. Simple old-fashioned grinding job does the trick here well enough, these engines have carbs that really SUCK (as in: having a real good fuel draw)...

Fly forever on an 8 oz tank, and effortless single flip starts galore...
Jun 15, 2021, 02:45 PM
AMA 46133
SeismicCWave's Avatar
>>Given the use of the word "petrol", assuming he is either British or at least European, he can send it to me and I'll convert it for him. Simple old-fashioned grinding job does the trick here well enough, these engines have carbs that really SUCK (as in: having a real good fuel draw)...

Fly forever on an 8 oz tank, and effortless single flip starts galore...<<

Exactly! I read "petrol" and figured the Op must be on your side of the pond (when you are not visiting Indonesia). So you can do more good things with your knowledge in gasoline conversion. A good carburetor that sucks is a good thing. Otherwise you need to fit a pump.

I really should look for the gasoline pump made by Perry.
Jun 15, 2021, 03:22 PM
A man with too many toys
Quote:
Originally Posted by MarioSWD
Hello,

I have an old os fs 120 engine like in the picture.



The engine is complete and I don't really know what to do with it. I wanted to change to petrol, but I decided to renovate it and try to fly. I am looking for information about this engine, some suggestions and, above all, operating instructions. I can't find it on the internet. Thank you for your help.

greetings
You need to find out what it's worth before making any modifications. Some of those old ones are collectors items. If modified it would kill any collectable value. Just something to investigate before making any non-stock changes.

.
Jun 15, 2021, 04:39 PM
No more wasted spark 😉
ClubFlyer's Avatar
Here's the OS FS 120 Pre-Surpass pdf manual. That will be $1.23
Jun 15, 2021, 07:11 PM
Registered User
Thread OP
Quote:
Originally Posted by RC Man
You need to find out what it's worth before making any modifications. Some of those old ones are collectors items. If modified it would kill any collectable value. Just something to investigate before making any non-stock changes.
.
That's why I haven't decided to modify it yet. There are few "collectors" in my country who will appreciate the advantages of such an engine. Maybe I will put it on some auction site ...
Jun 15, 2021, 07:13 PM
Registered User
Thread OP
Quote:
Originally Posted by ClubFlyer
Here's the OS FS 120 Pre-Surpass pdf manual. That will be $1.23
Thank you so much it will help me.

Brutus:
Is there any instruction to modify such a gasoline engine? I have the right background, I could handle it.?
Jun 15, 2021, 10:54 PM
Still gassin' it.
Look for threads under my previous forum name (Brutus1967), there is one about modifying glow engines to gassers. It is no big deal, I can do one in about 1 or 2 hours with basically a Dremel and my bare hands and I would not be exaggerating too much...
Jun 16, 2021, 03:34 AM
Registered User
Thread OP
Okay, I'll be looking. How about the durability of such an engine after conversion? and what about cylinder cooling? such a glow engine has a smaller cooling surface than gasoline.
Jun 16, 2021, 06:19 AM
Still gassin' it.
Quote:
Originally Posted by MarioSWD
Okay, I'll be looking. How about the durability of such an engine after conversion? and what about cylinder cooling? such a glow engine has a smaller cooling surface than gasoline.
I run 10:1 fuel/oil ratio in all my converted glow engines, and several of them are being run a LOT... I have the feeling, durability is excellent, better than on glow fuel, and at the very least rust or treatment with after run oil is totally a thing of the past. So is the need for storing of unused engines. They do not get stuck after a while.
For most applications you can without issues run 15:1~20:1 but I like to keep a single fuel, so I run the same mix, and I have not had any issues with it.

Heat is a bit of an issue, you cannot run full power continuously, but if you have even a halfway decent throttle management, there are no real limitations.
Cowled engines however, MUST have careful baffling, and cowlings are not recommended for slow flying planes (not enough static pressure to generate sufficient airflow through the baffles).

Some of my engines can run full throttle continuously, most of them can run around 80~90% throttle continuously.
All of them, with decent throttle management can run full throttle long enough (30 sec or so) to get out of a hairy situation.

My engines:
ASP fourstroke 30, 52 (2x), 91, 2-stroke 91, FT160 and AR400
OS FXi 46 (with true ABC piston set from ASP) and SF40 ringed
Rotorstar Apache 56.

The ASP 30 and OS FXi can run full throttle continuously, for reasons I do not fully understand, all others need a bit of restraint on the throttle (but only a little).

None of them have real issues, all are easy starters, frugal and dead-reliable.

I have modified in the meantime maybe 25 or 30 engines for customers, ranging from a 50 year old baffle piston SuperTigre 45 till Saito 180 and everything inbetween. Still have to receive the first negative feedback.

You can check out my YT channel (rigididiot). With very few exceptions, everything you see there dated after 2016 (and some of them even before that date) is running gasoline
Jun 16, 2021, 07:31 AM
Registered User
Thread OP
Thank you for your kind reply. What kind of CDI kit do you use for such conversion? Do you also remake the carburetors in any way?
Jun 16, 2021, 01:59 PM
Still gassin' it.
Quote:
Originally Posted by MarioSWD
Thank you for your kind reply. What kind of CDI kit do you use for such conversion? Do you also remake the carburetors in any way?
I use the bogstandard RcExl ignition units,, for fourstrokes, I thermally isolate the carb from the engine (minimize metallic contact to the engine frame with either plywood or plastic spacers), and I regrind the groove in the barrel as per this vid (not the best vid I ever shot):

Grinding a carburettor barrel (2 min 6 sec)

For total clarity: although I am using a cut-off wheel there, I am using the side of the wheel, not the cutting edge. Hard to make that visible on video, but the grinding action is by pulling the tool to the right, against the side of the groove, making the straight groove a bit rounded.
The job really is not that much more than as shown, and if you take small cuts at a time, you might need to repeat it a few times to sneak up on a good curve.
It is a bit a matter of getting a feel for what is needed. My first engine, it took me several small steps before it got where I wanted it to be, but nowadays I basically cut them freehand in one go.

It is advisable to double the spring behind the carb barrel. This can be done with a light conical spring, the same as used in some ME8 sparklug caps for contact improvement.

Here are the "before" and "after" vids of that particular engine of the grinding video.
How it ran before modding the carb (0 min 56 sec)

How it runs after modding the carb (1 min 50 sec)


For engines that have muffler pressure, you need a "craptrap" between the muffler and the tank to prevent fuel pollution from exhaust crud and water.

2-strokes usually need no modification, unless a possible remote needle has metallic contact to the engine. In that case you need some isolation there too.

Tanksize can be halved, which will free up space for the ignition.

A few things that are very important to take care of, but have very little to do with the modification itself:
-eliminate all play in the throttle control.
-use a slight slow down on the throttle in the "open" direction, as gassers hate rapid throttle movement
-Make fuel tubing as short and straight as possible, NO inline filters, but use a felt clunk and a 3 line tank set-up.
-ingnition timing 28 degrees.


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