O.S. 120 Surpass Failing after hot.
 

Dear all,

My OS120 is installed on a f3a plane and had always performed great, but two weeks ago, it started to oscillate after 3 or 4 minutes flying.
Due to the lack of fuel available in my town, I bought a gallon of 30%nitro 20%oil helicopter fuel.
After that, the problems began.
The high speed need seems like having no influence over tuning on any rotation. I can move it half turn either way with rotation change.

Any idea of what could be happening?

Thanks
Mauricio

RE: O.S. 120 Surpass Failing after hot.
 

Which 120 Surpass do you have. Pumper? The reason I ask is that the first two versions of the pumped version have a mechanical pump and the seal would harden up and while the engine was cold, it would leak raw fuel into the crank case. The engine would start fine, but wasn't responsive to tuning. Once the engine warmed up, then the seal would start working but because it was running rich from the get go it would suddenly go lean. You can see the raw fuel bubbling up the crank vent to the intake manifold when it is leaking. On the later version, it has a diaphragm pump, and if the diaphragm is damaged, it too will leak fuel into the crank case but it continues to leak no mater how warmed up the engine gets. Tuning is impossible, as the secondary supply of fuel, IE from the crank case vent, bypasses the carb, so you can't adjust around that.On the diaphragm pump, it used to be available as a replacement part. Not the other two pumps though. I made a diaphragm pump for a friends 1.20 and it worked quite well. If you are interested, I'll send you the instructions for that pump. Don

RE: O.S. 120 Surpass Failing after hot.
 

Dup post. Sorry

RE: O.S. 120 Surpass Failing after hot.
 

Hello CampGems, I thank you for your prompt answer.

Some more description about the problem, It after hot, it gets one second rich, one second lean, one rich one lean, for good...
Yes, it is a pumper, but I couldn´t tell wich version it is, so I took some pictures, I hope you can Identify it for me... My guess is that it is the first version...

Thank you
Mauricio

RE: O.S. 120 Surpass Failing after hot.
 

I don´t know why, but I cant upload all the pics at once.
uploading another now.

RE: O.S. 120 Surpass Failing after hot.
 

RE: O.S. 120 Surpass Failing after hot.
 

one more...

RE: O.S. 120 Surpass Failing after hot.
 

Your engine is the O.S. FS-120 Surpass II with the C-13 carburetor. If the engine will not hold a needle setting, there can be a few things that cause it. If the engine does not have the needle properly-set, then it will surge at full throttle. The pumped engines must be leaned as far as possible without RPM drop and left there. You do not lean and then richen.

Surging could also be caused by a bad regulator. Unfortunately, parts for the C-13 carburetor have been long discontinued. It went out of production in 1997, when the FS-120 Surpass III was introduced.

Fuel with 30% nitro would be considered a bit too "hot" for that engine. When you go over 15%-20% nitro, you gain nothing. Originally, the carb was set up to accommodate 10% nitro and 16%-20% oil. Most modelers used fuel with 15% nitro and about 18% oil. Try using a fuel with a lower nitro content to see if that helps.

RE: O.S. 120 Surpass Failing after hot.
 

Bax,

In this case, if I let the engine to cool down, and fire up again, it goes fine for another 3 or 4 minutes and them starts all over again the lean richen feel, but the needle is stuck in place all the times.

Assuming the problem is the regulator, could you please send me some schematics and parts list for it?

Thank you
Mauricio

RE: O.S. 120 Surpass Failing after hot.
 

Mauricio, one thing to try first. Get two fuel line T's. Put on one the line from the pump to the carb, and the second on pump return to tank. Now connect these two T's with a slightly smaller line. This will reduce the pump to regulator pressure a bit and "may" help you out. IT worked for my Surpass II. If that fails, You may need to tear down the regulator and clean it up. It is very delicate, and parts are not available.


I do have a set of instructions about how to "rebuild" this regulator and it may help. I did it on my engine, but it turned out to be the pump seal, and the T's above resolved the problem, but I don't think it is a "fix", but just a bypass for now. The T's were a suggestion I picked up from an Australian member of this forum a couple years back, who said that the OS rep there had recommended it. If you would like the instructions on the Rebuild of the regulator. PM me with an Email address and I'll send you the ones I used from another member on the is forum.

Don

PS, replace the blue crank case vent line with a clear line so you can see if fuel is bubbling up out of the crank case. This is important as it will tell you if the problem is a pump or regulator problem.Don

RE: O.S. 120 Surpass Failing after hot.
 

CampGems,
I indeed appreciate your help and yes, I want all the help you can give to me. If you don´t mind, I would like to keep the instructions over here, so others in need with simillar issue will be able to use your knowledge.

My e-mail is [email protected] - You can send the infos you got to there.

I will replace the blue line and see if it is bubbling.
I´m sorry if I make some silly question, but I have no experience with 4 stroke engines, I´ve never teared apart any 4 stroke before.

-Using the "T" solution, is because the pump and/or the regulator is over doing their job?
-Do you believe that if I replace the fuel line with some smaller inner tube would help?
-Does the valve openness has something to do with such issue?

Thank a LOT!
Mauricio.

RE: O.S. 120 Surpass Failing after hot.
 

CampGems;

First of all, I would like to thank you indeed for your help.

If you don´t mind, I would like to keep all the instructions over here, therefore, others with same issue, may get benefits from your experience.
My e-mail is [email protected], you can send all the instruction to there.

I´ll replace the blue line with a clear one as you recommended.
Actually, I´ll replace the whole tubing set.

I´m sorry if I make some silly questions about this engine, but I´ve never teared appart a 4st engine before.

here comes the questions:
- Does this engine has a piston ring?
- Could it be leaking or taking air from some joint faillure?
- Could the valve openness have something to do with the problem?

Thanks a lot!
Mauricio

RE: O.S. 120 Surpass Failing after hot.
 

We'd strongly suggest that you use a fuel with lower nitro. The factory set everything up for a fuel that contained 10% nitro and 16%-20% lubricant. We edited our post above to correct the fuel requirement. We had to do a lookup because we needed to confirm the fuel. It was the supercharged version that needed 20% nitro and 20% oil. The non-supercharged engines were best on 10%-15% oil, with 10% giving the best all-around performance.

There are no parts or diagrams for the regulator. O.S. never provided such. The regulator was supplied as a complete unit to the authorized service centers, only, and they were not permitted by O.S. to sell them. It was a service-center-only part. Unfortunately, they are no longer available anywhere. O.S. has not made any in a long time.

The original design of the pump system and regulator was for the pump to provide a fuel pressure 10 times greater than carburetor demand. This worked very well for a properly-operating regulator. Regulators could become stiff if they were in storage for several weeks or longer. It could take as many as five or six tanks' worth of running before they would become flexible to operate properly. The main symptom of that was a very poor idle once the engine was set properly.

RE: O.S. 120 Surpass Failing after hot.
 

OK Bax, Lowering the nitro will be my first try, as long as I don´t need to change anything.
I´ll post the results in here later on.

Thanks
Mauricio.

RE: O.S. 120 Surpass Failing after hot.
 

BAX,

What is the valve cover screew size?

tkx
Mauricio

RE: O.S. 120 Surpass Failing after hot.
 

Dear all,

After some set backs, I finally had the cance to test my engine with FAI fuel and 10% Cool power fuel, the results were the same.

Any other tip or trick?

If there is nothing else I could do, I´ll replace this with a Saito 180 that I have on the shelf.

Thanks
Mauricio

Dear all,

I had that OS engine set on the shelf since 2013.
I've been involved with many other projects, including a master Degree in Corporate Governance.

Well, A friend of mine disassembled the whole engine, cleaned it up on Ultrasonic equipment, replaced o'rings and bearings.
It is now ready to be tested.
The problem is that I don't have the schematics for the fuel lines.

Could someone here help me out with that issue?
Please, find attached some pictures of it to facilitate...

Thank you
Mauricio

I believe I may have the manual. Let me look for it - I will let you know if I find it.

Dan

Hello Dan.
I will be waiting.
Just in case you wanna send it to my e-mail, it is [email protected]
Thank you!

I found the manual. Its 5.05 Mb files size exceeds the forum's 5.0 Mb size so I can post it but will email it to you. Good Luck.