Help My OS 65 Keeps Overheating
 

Aloha RCU Flyers,

I have a persistent overheating problem with an OS 65 on my 61 size Escapade. It runs fine for a few minutes and sometimes even a few flights then the engine really loses power. After landing I noticed the engine was very hot to the touch and I got a reading of 230 degrees F on the temp gun (after throttling back and idling for half a minute or so). I have tried running the mixture as rich as I possibly can and still fly the aircraft but I have the same problem. I do have a cowl on it but I cut off the top to fit the motor and let it breathe. I have attached some pictures of the cowl to get some feedback. I run Cool Power 15 % Nitro fuel. I am out of ideas at this point and need help.

http://www.rcuniverse.com/forum/atta...mentid=2133541http://www.rcuniverse.com/forum/atta...mentid=2133542

Faulty carb ?
Air leak somewhere ?

Is there a fuel filter installed? I don't see one.

Nope speed, I'm not running an inline an inline fuel filter on this model.

More is needed about your tuning. Are you a pinch test tuner? Are you a tach tuner? Do you tune by ear?

When you say as rich as possible what is the data (reasons).

How old is your fuel tubing? How do you store your fuel? What Prop are you using? What glow plug? Besides Aloha, where are you (weather conditions, yes one might guess)?

The simplest reason for leaning at a while into a flight can be a hole in the tubing, brass or line, inside the tank that becomes exposed as the fuel is depleted.

Try tuning with 1/2 tank, then fill it.

These are a few quick thoughts.

1.) I use a 13X6 prop for this engine (recommended)
2.) I usually tune by ear. I listen for peak RPM then back it off a little. After the engine kept overheating I really richened it up. I have tried several setting between just below peak RPM to just inside the threshold of two cycle operation (right after the transition of four cycle operation into two cycle).
3.) The fuel tubing I use is about three months old.
4.) I use a # 8 glow plug.
5.) Yes I am in Hawaii. Temps average in the high 70's to low 80's with approx 70% humidity this time of the year.

It sounds a lot like an air leak in the fuel supply. I'd start with the simplest first, replacing the fuel lines, both the pick up line in the tank and the supply line to the carb.

Then move the search to the carb: disassemble the needle and check the O-rings for fidelity. Replace any that are not perfect. Also check the O-ring that seals the carb body to the case

Then take a look at the backplate seal. You may also have a bearing air leak but that's a stretch...

I forgot to mention that if you have an air leak that happens after some fuel burn, then the pick line in the tank is suspect. You might be able to see the air bubble in the delivery line to the carb

I have two or three thoughts on this problem.

1. bad fuel......try fresh fuel.

2. small particle(s) in the carb.....spin needle out of the carb and flush with fuel.

3. leaky or loose plug.......replace with a new one

I would try #2 first and then #1, followed by #3.

If these three fix attempts are unsuccessful, then I would search for an air leak. First in the fuel tank and lines, then the carb to case junction and then the rear case.

If all of the above fail, then maybe your engine is worn out.

better check that all the head bolts are tight. good luck.

A bent conrod can cause the piston to rub
hard on the sides making the engine overheat.

Jenny

Could be fuel foaming.
What is your flying style ?
Like where's the throttle at most of the time?
Half ? full? between?

Check the compression. Bring it to compression TDC and see if it holders for at least three seconds. Overheating is a sign of a worn out piston & sleeve. If it is good , look for something else.

Is the fuel tank mounted too low in relation to the carb? It may be fine when full but have trouble drawing fuel as the tank level diminishes. I've also seen engines where the pressure tap was obstructed (from the factory) leading to poor fuel draw.

Remove the needle valve assembly, the whole thing not just the needle. Most likely you will find some white fibrous material around the needle. Clean, re assemble and install a filter.

as stated, try new fuel, check inside the fuel tank and delivery lines for a pinhole leak, check the case for an air leak, check the carb is clean, make sure your needle valve isnt vibrating with that collar on it. I have seen them start to leak at certain rpm due to a harmonic vibration, let in air and poof deadstick. Put a piece of fuel tubing over the threads to help stop this.

Carbon build-up on the piston/sleeve? Worn bearings?

This is puzzling, especially as you have stated that you have flown the plane at a tuning setting that just has the engine breaking from a 4-cylcling state into a 2-cycling state. If that is truly the case and it is staying at that tune throughout the flight, then I wouldn't think you are having problems with holes in tubing or debrie in the carb. Now if the tune is changing, i.e. Going lean, then the tubing/dirt issues others have raised are correct.

I would tune it so it is just breaking into 2-stroke, take it up and fly it vigorously for 3 minute or so and then land. Check that it is still at that rich 2-stroke. Take off and repeat until you are about empty so that you are checking at all tank levels. If the tune is consistent, then I would go with Scott Douglas's thought?

A thorough tear-down, cleaning, and overhaul (new bearings, possibly more) to include carb, may solve your issue.

Are you the original owner? Have you flown with this engine before (in another airplane) without any problems? How much time on the engine?

Lars

PS: I would add an inline filter and never run an engine without one as they are easy insurance.

All it takes is a pin hole in the fuel tubing. Look real close where the tubing might be touching the engine, you might just see a "flat" spot. If you do that's it. In the past I spent hours trying to figure out why everything was ok and then not.

Hi Lars,

Yes I am the original owner of the plane and Engine I bought both of them brand new. The aircraft/engine have approximately 30 flights so they are both relatively new. I took apart the fuel tank and the pickup line looks fine and I verified that the stopper is sealed properly to the tank. The bolts on the cylinder head are fully tightened. I'll fly it this Saturday as you suggest. The first 5-6 flights went fine after that is when I started experiencing the loss of power and overheating

Also look close at the fill line. Looking at the picture it looks like it might be rubbing on the engine. If I were you, I would just go ahead and change all of the tubing. It's a cheap and easy fix for something that can make you crazy.

There isn't any play where the fuel tank is installed. It is a very snug fit on the Escapade changing the level where it it sits would require some modding.

I usually keep the throttle between half and full. This is my first low wing nitro plane after moving up from an Avistar Elite. I don't do any aggressive sport flying. Just some rolls and loops. It's a hame when this plane was flying well it's extremely fun.

Tried #1 and #3. Looks like I have to take apart the carb.

First off I would change the size of the tubing. If you are using 1/8" Id, then I would go to 5/32" Id. Most .60 to .61 glow engines run 11X7 props. A 13X6 seams a little large for a .65. Do you hold the nose up when you adjust the high speed needle? I do this every time I fly glow powered models. Lean it until it just starts to clear it's self out then stop. It might sound like it's not enough power when it is on level ground, but it will lean out when you get to altitude.....

Larry/Instructor

Hi Larry,

The recommended prop sizes for this engine are 12x6, 13x6-7 and 14x6. Wouldn't a smaller prop cause the engine to operate a higher than acceptable RPM and overheat? I typically do hold the nose up at an angle when tuning. So you suggest running a wider tubing for this engine?