I have had 3 engines go bad on me in the last 3 months, first an enya 25 on a canard, dead sticks , then an os 46 on a super sport gp, after 20 seconds of full throttle on bench flam out right there and low compression. and last a 61 os at idle shts off high end OK. Im useing a good morgan fuel, I dont have problems with 4 other glo planes of same size and smaller even a 15 runs good. Can an engine just wear out that starts ok, runs ok for a while 1/3rd tankfull gets to hot maybe or looses compression,then dead sticks , and then eventually dont run after 20 seconds on the bench? my prpblem now is with a supposingly good os 61 in good condition with lots of compresssion new plug f8 and all new fuel lines, it just dies at idle but runs better a high end. its on a new twister hang 9 arf and I dont want any dead sticks. whats the voo doo. Thanks any one ][/img][img][/img]

First, it would help if you structure you sentances a bit so we can understand you better.

To answer what I think you are asking, no, you can't shell an engine out in seconds unless you are doing something really really wrong. They do not come out of the box ready to just run, some take some tinkering with the needles. You need to get them set right so they run right. If you can't get it, get help. It will save you a lot of time and trouble. It would be too hard to explain here how to make them run correctly not knowing anything about your experience. It sounds like you are new and need some help from someone local though.

If an older engine has been sitting around for a while, rust will form in it. Part of the engine is aluminum and part is steel. You know what happens when you put dissimilar metals in contact with each other . One will start to oxidize, or rust. The steel part of model engines will begin to rust after months of storage. Later, when you try to use the engine. The rust will break loose and and find its way to the ball bearings where it might cause them to skid along and create flat spots. And the bearings themself can rust. If an engine starts fine, runs a few minutes, and then over heats, your ball bearings might need changing. You can generally turn the engine by hand and very carefully feel for any snag .

[:-]The really really wrong part I do agree with like broken fuel lines in the tank or loose carb or bent needle valve or blown head gasket. I have had a lot of flying time from control lines to RC, I even had an experienced engine person set one up for me and it died a month later. these engines Ive been having trouble with were given to me from the guys in my club, they never gave me any information on them as there history, they just said they came out of a running airplane. what Im trying to figure out, is when an engine wears out the cylinder sleevs or piston, does this happen gradually or just a sudden dead stick and then no compression as when it was new and then the end,now its time to replace parts? I just cant buy that its all the tiny little percise settings of needles both high speed and low speed when the engine is a strong running tight engine, I have had engines even when slightley rich or lean settings corrected with a few clicks on the high needle while holding the nose of the plane up .

They all came from running airplanes[:-] It might be they were all running into the ground. As the planes they were in were crashing

Just kidding

Try asking the people that sell you used engines for a "carfax" type of info on the engine. They might know that a particular engine has a high PIA factor, for one reason or another

good Idea ,thre is some place out there that sells nothing but used engines

http://www.bobsengines.com

Uncle Bob buys, sells, and trades engines of all makes, models, and vintage.

Over lean kills engines.

Don't know of anything else that ruins compression suddenly.

right, you always richen a mixture for it unloads in flight

If you don't know how to tune the engines yourself, then there are HOST of things that could be causing the problems. Lean runs are probably the most common problem with pilots that don't know how to check the high speed needle. Many things can affect the high speed needle setting, temperature, humidity, and barometric pressure being the most common. You could have a blockage in your high speed needle valve. That blockage could be from debris from a fault fuel pump to bad fuel line handling practices to worn fuel lines.

Lean runs cause several problems. The most common, and easiest to fix, is burning out the glow plug prematurely. For an engine that is running fine, and then starts deadsticking and transitioning poorly, these are the first signs of a bad glow plug. In my troubleshooting regimen, this is nearly always the first thing I look for.

In ABC engines (or ABN), the way they are designed has some self protecting features. A lean run will cause the cylinder to overheat, causing a loss of compression, which causes the engine to stop running. Again, this fits the description of the behaviors your describing.

What color is the exhaust from your engines. It should be white, not clear. If its clear, you're running too lean. What color is the exhaust residue? It should be clear or very slightly colored. If its black or dark brown, your running too lean. Can you hold your fingers in the exhaust stream an inch or two from the exhaust outlet (two strokes only). If not, its too lean. This is also a good way to check the quality of the oil in the exhaust.

Bearing failures on used engines are another major culprit to look for. An engine will run with bad bearings, but the metal particles can and will be pulled into the cylinder. These particles will ruin the glow element (at best) or score the cylinder and piston. The best way to inspect the bearings in a complete tear down. For a used engine which you have no history on, this is probably a must before you fly the engine. You can check the bearings by removing the glow element and then turning the engine by hand. This will give you a feel for the bearing condition. Any grinding or roughness should be reason for suspicion.

Finally, peeling of the nickle or chrome from the piston liner is easy to look for. Simply remove the head and then remove the piston liner (after noting the orientation in the cylinder. Look for wear, scratches, or loss of chrome. If you see these, you may need to consider a new piston and liner set.

Good Luck,
Brad

Make sure your head bolts are tight too. If it just quit and has no compression at all, it sounds like you have a problem. THey don't normally do this. If you have had a few in a row do it, you must be running them way too lean. I have seen a lot of guys run engines really wrong, and I have never seen one just stop all of a sudden have no compression. It can happen, but it would be odd to have it happen a few times in a row.

I had a piston come apart one time and the engine still had compression and ran. These little engines take a lot.

Check to make sure your bolts are tight, your plug is tight, and that your fuel is good. If you run bad fuel, it could damage the engine. How old is the fuel?

the fuel was just bought from my local hobby store, its morgan 10% and works well with my other engines, I removed the glow plug from a good running motor and tried that , and no change, whats odd is a good friend and club member said thats strange that last week he saw how stong that engine was pulling my plane and now it dies at full throttle on the bench and has a new fuel tank and tubing,I blew out the carb and cleaned it I sealded the needle with a pice of fuel tubing, I Rtved the carb gasket area, this may sound stupd, but could my Idle adjustment screw have turned out or in and caused this problem?

Actually, I do.

Compression happens when the piston is going up and the valves close. It happens from there up. If the piston/cylinder seal is good and compression is suddenly lost, look to the only other seal that has to be intact for compression, the head to cylinder. Head bolts control this. Cracked head? Loose or lost bolt?

Compression also happens on the downstroke but is quite different. Nonetheless, look at the backplate bolts. And you'd still feel the compression of the piston going up.

Sudden loss of compression could be a broken ring or a badly scored piston or cracked head or lost headbolt. Could also be a hole burned in the piston.

[:-] well I have a 2 cycle without valves ,what about the low needle moveing or turning out or in , could this have happened?Ill have to check it >

Yup, overly lean equates to overly HOT too... something he mentioned.

If the tank isn't absolutely cleaned out after assembly, little flakes of brass can travel to and jam in the spray bar. Have you tried blowing it out ? Sometimes old fuel will just gum up the spray bar or carb fuel inlet.

[&:] yes matter of fact I ran a small wire music wire though the Idle spray bar at the field when it happened, I blew through it ,I sprayed wd 40 thrugh it and its not clogged

Nine times out of ten an engine problem is actually a fuel tank/line setup problem. Double check the tank to make sure everything is installed properly and in good condition. Check fuel lines for cracks/pinholes.

Then again, a bad tank setup will not make the engine loose compression. Are these engines really loosing compression that quickly? I've only heard of instantaneous compression loss with four strokes. Really the only way with two strokes is to have the backplate or head come loose.

If its not the tank. ANd its not the carb. Then I still feel its the bearings. Is there another carb that you can bolt on ? Bad bearings will typically run OK for about 3 or 4 minutes, then the case heats up and the timing goes bad. How long did you say it runs ?

ok Ill recheck the tank ,thanks for the information

thanks Ill recheck the tanks and lines , right now when it was on the bench the other day after about a 30 second or more of full throttle then it would die