O.S max 46la engine problems
 

I have a O.S max 46la engine that is only about 8 months old. It had been running fine but now when i get it started up it runs fine for a little while and then just looses all power. I can hear that it is not running right. I have tried to change the needle vaulve setting but that doesnt work. I have put a new glow plug and am running new fuel (10%) which is what i have always run.

RE: O.S max 46la engine problems
 

I think the engine gurus will need more info... is it stopping when running at full throttle or at idle? Does it gradually slow down and start blubbering or is it a quick death? If you start the engine and let it run, then hold the airplane nose up at full throttle, do you hear a slight increase in RPM or does it just die? When it dies, grab (carefully!) the head...is it really, really, really hot or just barely warm?

Suggestions... replace the fuel line in the tank and to the needle valve/carb. Adjust needle so that there is a slight increase in RPM when held nose up at full throttle and it continues to run like that. Once you get the needle adjusted, you shouldn't have to adjust it more than a few clicks in either direction.

Wish I could help more...

RE: O.S max 46la engine problems
 

Check the screws to the back cover plate. They have been know to loosen up and cause a similiar problem.

RE: O.S max 46la engine problems
 

a caviat to that is to check the head screws also, I had some come loose before. Sounds like it is running a bit lean and getting too hot.

RE: O.S max 46la engine problems
 

Does the engine die? It could be a kinked pressure line.

Sounds to me like it may be wearing out. Once the sleeve and piston wear enough what you are describing may be happening. As the engine gets up to operating temperature the fit between the piston and the sleeve can open up a little too much and you lose too much compression. There is not much that can be done but replace the piston and sleeve. I inhertited an LA 40 with a similar problem. The engine looked like it had fought in Iraq and returned. A new piston and sleeve made the engine run like new.

I'm not saying that this is the problem, but it sounds like a good possibility. The engine is pretty new but may have ingested some dust or had some lean operation. I would check fo air leaks in the engine (backplate, head, carb area), bubbles or debris in the fuel lines, and inspect the tank and plumbing. I would try to rule everthing out before piston/sleeve replacement. You may want to put the engine on a test stand and give it a try.

Pull the muffler off and look at the piston. If you see scratches or if the piston is very dark, you may have found your problem.

RE: O.S max 46la engine problems
 

Sounds like it could be a small hole in clunk line, fuel burn down to it then it leans out. Also check all screws especially backplate and carburetor. I have had all these problems happen to me. Also take both fuel line off needle valve and back flush with fuel, I had that problem to, it was shaving off of tank. Good Luck! Jim

RE: O.S max 46la engine problems
 

Hi!
Give us more information...glowplug, propsize, fuel.
Regards!
Jan K
Sweden

RE: O.S max 46la engine problems
 

Lots of great suggestions.

How long does it take to start loosing power?

It could be a worn out piston/liner as suggested, but be sure to check over the fuel system very carefully first. 8months is an awful short time to wear out an engine unless it's been sucking in a lot of dust or been planted and not cleaned out fully. (unless you're the type who flys 3-4 flights every day). If the engine doesn't die, just looses power for no apparent reason, and no matter how rich you set it, and you see nothing wrong with the fuel delivery, this becomes more likely. Fwiw, a piston/liner swap isn't hard to do, and the parts cost $35 from tower right now. If you really suspect the engine is worn out, try running the engine on a stand first to make sure, or at least hook up an external tank on the airplane with all new tubing, and run it that way (I don't suggest flying that way, just run the engine a bit).

Quick question, when you replaced the plug, did you look at the old one? Was the plug element still in the plug or was it missing? Often times the plug element will blow out of the plug and just go harmlessly out the exhaust port, but sometimes it will get stuck, and can score up the piston/liner.

8months, flying a few flights most weekends is about the right amount of time to start seeing things like the loose or cracked backplate (those darn plastic backplates), loose head or carb, or such. I've also seen holes appear in fuel tanks from rubbing against screws inside, or fuel lines developing holes due to vibrating against the metal fuel tank tubing or other parts of the plane or tank. 8mo is a bit short for the fuel tank stopper to have worked loose, but check it anyway, they sometimes loosen up over time. Also check the muffler.

A good thing to look for is dark colored oil or gunk that has started to appear around the engine compartment that wasn't there before. That would point to loose engine parts.

On the list of silly things to check first, make sure the clunk isn't stuck at the front of the tank.

RE: O.S max 46la engine problems
 

well basically it starts up fine and i can actually take off with it. But after a couple of minutes i can hear the power drop like its just above a throttle. When i land the motor is still running but very hot. I have tried to run it richer but it still seems to have to power. I have also done the trick where you hold the nose up to see if power is lost and that doesnt seem to be a problem. Is there anyway to clean the engine up? I have it mostly taken apart and there is alot of black residue inside but I have not seen any metal or anything. I am also running a hot glow plug which is suppose to be able to let you run at a richer setting. and I use 10% fuel. My brother also flies with me and he uses the same fuel and glow plug in his o.s. max 40 la.

RE: O.S max 46la engine problems
 

With the engine apart you can test the fit of the piston and sleeve. Move the piston up in the sleeve and it should catch well before the top. I could push the piston all of the way to the top with little force on the 40 LA that I inherited.

RE: O.S max 46la engine problems
 

if it starts ok &runs through part of the tank until it begins to show problems , its a fuel feed/tank problem. either the tank may have settled into too low position or you have hole in the feed line inside the tank.its causing it to run a bit too lean , lose power &heat up.

RE: O.S max 46la engine problems
 

If you are using a castor-based lubricant in the fuel, it is possible that varnish is the problem. Castor varnish slowly accumulates on the piston & sleeve creating internal friction and robbing the engine of power -- the symptoms can be similar to yours. Is the piston &/or cyl sleeve covered in a brown deposit? If so, that could be castor varnish. Dissassemble the engine & simmer it in a pot of auto anti-freeze for several hours (do it outside), then wipe or brush of any remaining residue. Clean & lube the parts with ATF, then re-assemble & try it.

RE: O.S max 46la engine problems
 

May be your engine is overheat. Make sure you are using a lubricant more than 18%. Most of the plane in my club use 20-25% of lubricant with OS#8 glow.

RE: O.S max 46la engine problems
 

Hi!
The sympthom you describe is related to that the engine doesn't get enough fuel and is overheated. Simple as that! Check if the engine can hold its high speed setting when you hold the airplane straight up....
Check loose screws when engines is cool,not hot or warm! also check bad fuellines for cracks and that all lines are as short as possible. Never use an in line fuel filter on board the airplane ...always filter the fuel when fueling.(Use a big paper filter inside the fuel-jar in your field box).
You should also put in a new Enya 3 or OS 8 glowplug. Prop 10x6, or preferably 11x5 or 11x6 if you fly a high winged trainer, APC props are recommended.
Fueltank 8 oz, mounted so that the center of the fuel tank is inline with the carb when plane sits horizontal.Very important! See to that you use lots of soft foam rubber around the tank. Never mount a tank direcly to the fuselage formers like seen in so many ARF airplanes.
Always use 3 line fuel system with two clunks running parallel, one to the carb and one to the pressure nipple on the silencer. Third line going to the top of the tank is for owerflow.
This tank system is called a "Uniflow" tank set-up and it is better than an ordinary 2 line tank hook up.
Never use a plastic spinner as thse are notorious for giving balance problems.
Also check fuel.
Hope this helps.

Regards!
Jan K
Sweden

RE: O.S max 46la engine problems
 

Be careful here. Too much oil will cause an engine to run hotter than it should. The reason is that he oil doesn't combust, and doesn't compress, so it raises the engine's compression, and that causes more heat. It may not make a lot of sense, but I've seen this demonstrated first hand.

Also, the reason I didn't suggest an overheating problem the first time was that the engine had been running fine for quite a while. If the problem was heat, I'd expect it to have shown up before. However, if something changed, heat could become a problem when it wasn't before