tmenold

My Feedback: (17)

I recently bought an rc plane with an O.S. Max-55AX engine on it. The person I bought it from thought the engine was bad cause he couldn't get it to start. When I got home I noticed that he had a remote fuel filler on it and there was quite a bit of fuel line between the tank, the filler, and the carburetor and I don't know if this had much to do with it not wanting to start but I primed it a bit by plugging the exhaust and it fired up fairly quickly. Now the real issue is trying to keep it running smoothly. I've messed with the needle valve quite a bit by richening and leaning it trying to find where it runs the best and whenever I try to idle the engine down, it immediately dies. I can't get the engine to come below 1/2 idle when it dies. The engine does have a tuned pipe on it but I wouldn't think that has anything to do with the way it runs/idles. I also bypassed the remote filler and ran a short fuel line from the tank to the carburetor which didn't seem to make a huge difference. I'm not a huge engine guru but was wondering if there are other adjustments I need to make to the engine to get it to run right. This engine does not look like it has been over used so it doesn't even look close to worn out. Any suggestions on where I can go from here would be greatly appreciated. Thanks!

Trent

Cyberwolf

My Feedback: (4)

Have you adjusted the low end needle as well as the HSN? You could have a air leak someplace too, are you getting good tank pressure. Are the bolts to the backplate and head tight? is the carb oring making a good seal and the screws tight? I loosen them up a little and push down on the carb while I tighten them to get a good seal on the oring.
Also what plug, Fuel are you running?

tmenold

My Feedback: (17)

Cyberwolf,

I'm using Byrons Fuel (20% Oil, 10% Nitro). Not sure one the glow plug, but I'll replace it and try again. He air leak is a good idea, i'll check that also (fuel tubing and tank). When you ask if I've adjusted the low end needle and the HSN (not sure what that is) the answer is no. I did mention that I'm not a huge engine guru, so anything else other than adjusting the needle valve is new to me. I quick skimmed the manual and didn't find a spot where to start with the low end needle valve. Would this be the tiny screw close to the needle valve? Thanks for your ideas so far, I'll try again some time soon and report back.

Trent

MinnFlyer

My Feedback: (4)

The "needle valve" is actually the "High Speed Needle Valve" (HSN). On the opposite side of the carb is the throttle arm. In the center of the throttle arm is a small brass screw - that is the "Low-Speed Needle Valve" or "Idle Adjustment".

Try turning it 1/2 turn in either direction and try again. If it gets worse, return it to where it was, then turn it 1/2 turn in the opposite direction.

Once you see it getting better, make small (1/8 turn) adjustments until, when at a reliable idle, if you pinch the fuel line, the engine will increase RPM slightly for a second or two and then die.

estradajae

On the 55AX carb, the idle set screw is on the same side as the high speed needle

tmenold

My Feedback: (17)

Thanks estradajae!! I was wondering about that cause my HSN is set at a 45 degree angle and there's a tiny screw that goes straight into the carb by the HSN. That makes sense. I'll try again this week and and report back. Thanks again to all! Hope I have success!

Trent

Cyberwolf

My Feedback: (4)

I set the idle screw so it doesn't touch anything and use the radio servo to control the idle and have it so I can kill the engine with the radio. The only time I ever use that screw is for maybe bench running so I can't pull the throttle arm to far back and kill the engine by mistake.

gunneredwards

My Feedback: (4)

definitely sounds like a fuel problem, check the tank and fuel lines and see if there is an air leak. Just had this problem with mine.
dan

MinnFlyer

My Feedback: (4)

Duh, my mistake. I stand corrected

tmenold

My Feedback: (17)

Hey guys, sorry I never got this thread updated..... I just got back to working on this plane because I got frustrated with it and put it on the back burner while I flew my others. I finally had the desire to get it back out and work on it some more. After a bunch of adjustments and more head scratches we finally figured it out...... I noticed that I could basically completed close my carb and the engine would still "somewhat run/cough and sputter but eventually die. This told me that somewhere there is air getting into the fuel mixture to let this engine still run. The engine is mounted sideways on this airplane. My buddy and I decided to take the carb off and and a look at it. There are two screws that are supposed to hold the carb onto the engine (when the engine is mounted sideways, one is on top and one on the bottom). As I unscrewed the top screw I was able to pull the carb right out of the engine, exposing that the bottom screw was missing, letting a hole approx. 1/16"-3/32" wide open for air to be sucked into the engine while the throttle has the carb completely closed. I robbed a screw from one of my unused engines and the O.S. 55AX runs like a charm. I was extremely excited that the issue was really a simple one, it's just that I never picked up the plane to examine the bottom of the engine (since it is mounted sideways). And to think I was about to buy another engine for the plane and/or sell the plane at a discount..... SIGH...... Thanks for all your ideas cause I really did try them! Happy Flying!!! ;-)

fiery

My Feedback: (2)

Glad to see you had a happy ending.

moti.m

I have OS 55AX new engine  3 mounts only

At the begining it worked ok, after less than 10 hours the engine started heating
and extremely reduced power

 Even in very reach adjustment  
The braking was according to  instruction
The propeller is 11/8 according to  instruction
Never change the fuel from the beginning  (15% netro)
The compression is perfect
Everything including carburetor is clean
Fuel tank and fuel tubes are ok
How to solve the problem?

estradajae

Get rid of that 11x8 prop, use a 11x7 prop as it may be too much load, and not letting your engine develope full power. Also make sure your fuel has some castor oil.

moti.m

sorry my mistake i use 11/7 prop

Cyberwolf

My Feedback: (4)

We need some more information
Is the engine cowled in or open to the air?
Oil type and how much?
Glow plug ?
How far away is the tank from the engine?

Will the engine shut down by closing the throttle barrel?

JimmyZep

Any prop in the recommended range will work.

If your useing a quality fuel, whether it has castrol oil or not has NOEFFECT on the way it runs.

I have a 55AX with Cool Power 15% nitro and synthetic oil and it runs fantastic.

Its probably too lean.

Jimmy

freakingfast

My Feedback: (3)

The props in the manual are way too big "12x7-8, 13x6-7". OS admittedly explained this was done for noise reasons. But in my and many others opinion, this greatly reduces the engines performance potential and increases risks of engine damage due to over heating/pre-ignition. Much better props are 12X5 APC for 3-D, 11X7 S-2 series Master Airscrew OR 11X6 APC for sport, 10X9 APC for fast clean planes, 10X10 APC for quickie 500.

Some guys are getting away with synthetic oil only, but the next guy wont. One lean run and it's been hurt. The user may never know because he has nothing to compare it to or he has low expectations.
This is an ABN type engine and it's not too forgiving of a lean run without some Castor oil as part of it's oil make up.

moti.m's engine could be lean. But Cyberwolf asked some questions that need answering

JimmyZep

Your correct, maby I should have said that every time I see someone on the forum
with an eng problem someone allways will say better change your fuel to castor oil.

While it my be the better fuel to use its not going to solve the problem at hand.

Jimmy

freakingfast

My Feedback: (3)

Agreed.

"You should also use a fuel that contains castor oil in the lubrication mix. Castor oil helps the engine run well and is the better lubricant for our ABN engines. All-synthetic fuels have been known to cause difficulties in running at times."

Source, OS website:
http://osengines.com/faq/product-faq.html#q2

Is all-synthetic fuel always the problem? Absolutely not, just one of many places to look.
Do I use all-synthetic fuel? Yes, on my Heli engines(rings) and after break-in on my ABC ducted fan engines.

moti.m

thank you

Cyberwolf

My Feedback: (4)

In my mind there is no doubt the engine is running to lean, we just need to find out the cause.

jaka

Hi!
Agree! You are running it too lean!!! Simple as that! It could be leak somewhere that makes the engine go lean ...or dirt in the high speed needle ...or a loose screw in the backplate or cylinder head. It could also that the engine has digested grit that has destroyed the piston.
So take the engine appart and have a look!

You can use a wide range of props for your OS 55, 11x6-14x5 is just fine, so it's not a too large prop problem.
Neither is it fuel. Over here in Sweden it's very common to use 10-15% all synthetic oil. Castor oil is very seldom used,except in pylonracing where the rules demands 20% castor oil! It could be that the fuel you use has gone bad from having the container in the sun or having the cap open so water (moisture) has poluted the fuel, but I doubt it!

Some advise!
Use fuel that contains 5-15% nitro. 15% nitro is overkill and 5% is just fine.
Castor or synthetic oil works equally well! To be on the safe side use at least 18% oil.
Use a 300-400cc tank and check all fuelines for leaks by sucking in and holding the tip of your toung for the opening. The tip should stuck!
There should never be any air bubbles seen in the fuel lines!!!!
Always mount the tank according to the "tank-mounting-rule"! If not you are asking for trouble!
Use an OS 8 or Enya 3 glow plug. These are not the best glow plugs if you want ultimate performance but good for reliable sport flying.
Use a 12x6 APC , Graupner cam-prop or Ram prop! Those are the best props available. See to that you always balance your props!
Use an alumium spinner nut! Never a plastic spinner without backplate!
See too that the engine mount you use has mounting arms that are parallell! if not, file the arms true! Otherwise the engine housing will be destorted when you bolt it down and engine heats up! (not that likely but anyway).

moti.m

Thank you very much for your educate advices
as I have  checked every thing ,OS Japan advised me to sent them the  engine for evaluation. 

jaka

Hi!
I would take it apart first if I were you!
I cannot think of an OS engine that is wrongly built! Haven't seen such engine in the 36 year I have been using OS engines, and as it ran fine from the start, it must be easy to fix it now!
I only takes 5 minutes to take the engine apart and see if there is something wrong with it. And the only thing that can be wrong is either a scorn piston comming from ingesting sand or grit , a bad ballbearing...or dirt in the high speed needle.

moti.m

Thank you again if i will find somthing I will inform