estradajae

Hi everyone,

here's the story:

I have a O.S 46FX that was laying around for about 3 years, and really it wasn't very used, so it's quite "new", and my dad and I bought a Tower trainer because he wanted to learn to fly and be my flying partner instead of my "mechanic" jeje, and I put the engine on this plane. I stopped using this engine because at that time I built a plane and I bought a magnum 46 xls that I enjoyed more than the O.S, but it was a sweetheart anyway, no problems at all. But in the tower trainer the engine want's to stop, it doesn't like to run more tan a minute or so, at full rpm looks like it has the same power as ever, idles good also, but if I transition sometimes it dies....if a go from full to idle..,.it dies...and also, at full throttle, it just dies.

I'm sure there is no adjustment problem, I mean I'm sure needles are ok, and this engine is quite easy to tune, so I started searching for leakages etc...I'm pretty sure at this point the problem is an air leak..search for the tubing..tank..everything is ok...so I decided to take the engine off the plane....I blowed through the carb and voila...I hear air coming from the front bearing, so that's where the leak comes from.

Now I have a doubt because I don't have a clear explanation or facts that make me think that the front bearing should be sealed or not...I mean, I've read here that some say that leak is normal...and others that say leaking is not good there.

What I'm sure is that if the engine stops suddenly when it seems to be working properly is an AIR LEAK....

anyway, I always use FAI fuel, I mix myself my fuel, and this have worked for years and my engines are happy with it, so fuel is not a problem, glow plug is a tower plug as usual and I'm using a 11x6 MAS...just like when it used to run flawlessly.

This engine haven't sipped more than 2 gallons, and bearings aren't rusty (use plain castor)....is time to get a new bearing set?

Thank you!

Jorge

Campgems

Jorge, the front bearing usualy isn't sealed, only shielded. Some air blowing through it would sound normal. Your problem is elsewhere. Any air leaks that will cause you trouble will be at the back plate, and the carb to crank case seal. Make sure these are OK.

What else to loook for.
1. Tiny air bubles in the fule supply line. This would indicate a fuel line problem between the clunk and the carb.
2. Runing to lean and over heating. It would be good to retune the engine as if it were new. Having sat for a few years, some fuel will turn to varnish and it may take a while for this to self clean. At least though go through the needle adjustments again and use a tach if you have one. If you don't lean the high speed for what sounds like the fastest speed and then go rich on the needle three or four clicks, enough to hear it start to drop RPM but not to much.
3. I may be good to replace the glow plug also

Don

estradajae

Hi Don, thank you for your answer.

Well when I packed the engine for storage, I washed it throughly and put 3 in 1 oil generously, so the engine was very clean inside.

I retuned the engine as usual, and it seemed to tune very well, but it just dies. I always use a tach and I can recognize when the engine is lean... so I'm sure its not lean... also it dies when idling, I mean, it just happens at any throttle setting and it does without advice, no symptoms that make me know if is lean or rich... but looks more that it just gets lean suddenly and stops... but just in that moment when it stops.

I found no bubbles in the line, but remember that in a remote you usually get small bubbles.

I've changed the plug also with no effect.

In a crash I broke the needle support so I'm using a new backplate with a new gasket (also the head gasket was changed since I bought the package)

I post the pictures, and you'll se that the engine is pretty much shiny... so old oil and residue are outside..

Flow passages are clean, no clogs and I see any problem at all, pressure checked the fuel tank and lines for pinholes or so... none of them found... and it's a shame...I haven't been able to fly this plane.

I feel the bearings are smooth and it's strange, to me the front shield looks a little recessed, see the picture, may cause it any problems? since the engine was new, it was that way.

Here are some pics.

Campgems

The nose bearing looks fine as long as it feels smooth. It is a shielded one side which is usually used. Fuel and air leakage is OK as it helps the oil get throught the bearing.

One of the guys at our fiels used to be tech support for Norvel engines. His trick to find air leaks is to use pertolium jelly and coat the suspected areas. It will seal things long enough for trouble shooting. Other areas for air leaks are the O-rings on the needle valves. They some times shrink with age. Again, coat them with a thick coat of the petrolium jelly and see if it changes things.

Don't ignore the tank and fuel lines. I once had one of my engines suddenly start dying within 30 seconds of starting. I worked and worked on it to find that I had crossed the vent and the supply and it would run as long as the vent in the tank was covered with fuel. I've also had lines go bad in the tank, one was only a week old and it broke just a bit right at the brass tubing.

Don

Cyberwolf

My Feedback: (4)

Can you kill the engine by closeing the carb off ? if so I would say you don't have air leak thats causing your problems . I do see some left over castor on the crank and a few other places. It dosent take much to gum up a carb and cause just what your experencing . I would do as already suggested run the engine in a rich 2 stroke mode for a few tanks and see if that won't help clean things out .
One other thing to check while hunting for air leaks is the O ring at the carb base , Good Luck.

estradajae

Thanks for the reply

Yes the engine can be shut down closing the carb barrel

But no, the engine is not gummed in any way...the carb is perfectly clean..i disassembled it and it was very clean, anyway i flushed it ...

JOrge

Cyberwolf

My Feedback: (4)

If the carb is clean good plug and fuel,the only other thing that comes to mind at the moment is the tank and lines .
or just the needles being a little out of whack.
Hows the compression ?
Also how is the engine mounted ?

estradajae

Well i took the tank off and it seems sealed and lines ok, I pressure tested it and found no leaks and problems....

The plane is a tower trainer...and the engine es mounted upwards, tank is located in the right position.

THe engine feels with high compression, and also when it runs, it runs well, with plenty of power. It's strange because at top speed it just stops...it can run for 20 seconds and just stops.

I thought it could be related to needles too, but I did the normal procedure, high end and low end, and it could be tuned accodrdingly, but after that, without advice it will just die.

Anyway I just changed the lines and after dismantling I put the engine again on the plane...hope this week I can give another try.

I've changed the lines also because the foot of tubing I bought at the LHS that used in this plane seemed to be a bigger size than normal, most likely the one I use in the fuel pump, so I changed it to a normal one, I think that could cause some trouble, so I changed it to a normal size tubing.

Hope that make the trick.

Thank you all

Jorge

blw

My Feedback: (3)

Jorge,

Don't forget the fuel line from the remote needle valve to the carb.

DarZeelon

Jorge,


Calling it a leaky front bearing just does not do justice...

It is not part of the front bearing's 'job description' to seal the engine... It is just a bearing, to locate the crankshaft, mostly in the axial plane.


When an engine leaks excessively through the front bearing, the problem is that the front rotary valve is not sealing properly, which means the crankcase/crankshaft/both are either incorrectly matched, or plain worn-out...

A leak is in the sense of either fuel/oil leaking out, or air being sucked in.

A fully sealed bearing will, in some cases, offer a temporary remedy, but the correct treatment would be replacement of the out-of-spec, or worn items.

In many cases, the real leak, which allows the engine to run-on, is between the carburettor body and barrel, or at the joint between the carburettor spigot and the crankcase...

estradajae

Thanks Dar....you're right.

I blowed through the carb inlet, and found no leaks other than a slight leak in the front bearing, I had to blow very hard to hear it, and it was with the cranckshaft port opened, so I guess the air is coming from the cranckase through the rear bearing and not from a poor fit between the case and shaft.

For all things said, bearing must be ok so

THank you very much,

Jorge

Sport_Pilot

It sounds as though the idle circuit is cloged with dirt, or just adjusted too lean. If the Magnum runs fine and the carb is the same size, try swapping carbs and see what happens.

jaka

Hi!
The culprit is in a way the FAI fuel you use. It makes it rather difficult to set the engine properly.
You would be much better off using some nitro. 5-10% is all it takes to have the engine behave much better.

estradajae

No Jan...

I've been using FAI fuel for the time I've been in the hobby and it is not the problem. I have no tunning problems, the engine tunes fine, idles fine and top end is fine, transition is fine, but the engine likes to quit.

Before the engine was stored, it worked ok, with the same fuel, never had any problems with it, but I started having problems when I put the engine on this particular plane.

I have other engines that run very well on the FAI fuel, and really, I don't think I need nitro at all, I've used it and see no difference.


Jorge

rainedave

My Feedback: (1)

I would put it on your test stand. It must be something with the plane vibration, fuel plumbing, tank location, etc.

David

freakingfast

My Feedback: (3)

Is the fuel fresh? Was the cap on tight when stored?

estradajae

The fuel is working ok on my magnum 46 xls and tower 75, also it was mixed last week.

I wish I had a test stand, but I don't have one, also where I live I cannot run it, I can only run it at the field.

Has anybody have had this kind of problem? I mean... engine runs good, gobs of power, nice idling, but suddenly it stops?

Thank you for your input!

Jorge

jaka

Hi!
The problem is the FAI fuel. You would be much better of using nitro as the engine is made to run on 5-15% nitro.
If you insist in using FAI fuel I would remove the headshim to have a bettetr running engine.The problem is the peaky performance curve you have when using FAI fuel. You get a much wider curve when using nitro which means all settings will be much easier to perform.

NM2K

My Feedback: (14)

Something else to keep in mind is that silicone fuel line grows with exposure to model fuel. After a while, it is possible for the suction at the fuel pick up in the fuel tank to pull the clunk against the rear wall of the fuel tank, shutting off the fuel to the engine. This can drive you nuts if you have never experienced it before.

Good luck finding the problem. Let us know what you discover as the cure.


Ed Cregger

Sport_Pilot

You should try an extra hot plug with FAI fuel and a low compression engine intended for 15%. Try an OS A3 or the Thunderbolt four cycle plug.

estradajae

THanks everyone for the inputs.

I insist, my problem is not tuning the engine, the problem is that it stops suddenly. The engine performed flawlessly before with the same fuel and plug (I use tower plugs).
Nitro fuel here will cost here more than the double of my fuel, and most of the time my wallet is so tight (i'm still student) so I have to keep cost down.
The 46FX doesn't come with various head shims, it just come with a single one, and the engine have never been run on nitro also, always FAI fuel.


You're right Ed, I noticed that with the lines I've changed, but the clunk seems to be ok, moving freely in the tank.

Sport_Pilot

From your first post.

This sounds like a lean mixture or retarded timing to me. I suggest removing the head shim and replacing the tower plug as it may not be as hot as before. Assuming the Tower plug is the same as an OS A3.

DarZeelon

Quote:

ORIGINAL: Sport_Pilot

...Assuming the Tower plug is the same as an OS A3.

Hugh,


The old Tower Plug WAS the same as the OS A3... The new Tower Power plug is a medium heat plug, equivalent to the OS #8 and made in Japan for Tower (probably by OS?...).

The A3 is the hottest plug there is... OS makes no plug that is hotter and hot plugs made by other manufacturers are no hotter than it is.
At most, the hot ones (such as the Enya #3) are only equivalent to it in heat-range.

wcmorrison

My Feedback: (2)

You say the engine has been in storage. I would replace the 0-Rings on the main needle and the idle adjustment. Both can allow air to be sucked in causing the mixture to go lean. You can use a piece of fuel tubing slipped on the main needle to seal that area -maybe 5 mm of tubing. In the case of the idle adjustment, I am afraid it is a new 0-Ring to fix that, if that is the leak area.

There can be only a limited number of places to develop an air leak: the back plate (cover), the carb throat (can seal up with some automotive sealant), the nose (some leakage acceptable and needed for lubrication), the seals (0-Rings) on the needles - both of them and that's about it. You could have a crankcase crack but that would be pretty obvious. You could have a bad seal on the back plate, even a warped back plate, there usually is a seal back there, some are paper seals, and some are very thin 0-Rings.

Cheers,

Chip

Sport_Pilot

Not sure but I think the Thunderbolt four cycle plug may be hotter.