Hey, I just found out the hard way why after run oils should be used. I bought a plane off a fellow member, and it came with a used GMS 47. It ran great for about 3/4 gallon of fuel, then i started having problems. At first, it was making a weird sound at low throttle settings. Then I had a deadstick on the down line of a hammer head. (it died when i chopped the throttle) and today, it just quit. half way through the flight. I never had a lean run, and initially suspected dirt in the carb. when i went to turn the engine over, it was really tight. It always had great compression, but it was tight all around. I just tore it down, and found the bearing in the very front of the engine had failed. The crank shaft was really rusty and corroded.
My guess was that this engine had been sitting for a long time without any oil in it. The fuel i use says not to use after run oil, but i do anyways.
So for anyone new to the hobby, or anyone who doesnt use after run oil, this is what will happen.

No, that's what CAN happen. But it can also happen if after run oil IS used. It depends a lot more on how the engine was stored.

It also depends on your environment too. Houston would be worse than Vegas due to the humidity.

dont chuck it out (if you are going to send it to me ), wd-40 the heck out of it that should get most of the rust/junk off the crank (let it soak for over night) , then get new bearings (may be able to wd40 those as well, but prob not, its worth a try) and you should be good to go.

is your conrod/piston rusting at all?

i cleaned a engine, that looked similer to yours. only it was a bushing engine
i dont use after run and none of my engines look like that

Omega fuel has after run oil in it

Tell me about. Today's high will be 102* with 98% humidity. I keep my planes indoors.

One of the reasons I left Houston! Indy is not much better though, but at last the humidity is not as bad. 90 today but feels like 106.

an oldtimer where i fly said Campbell Hausfeld air tool oil with one third Marvel mystery oil is the best you can get

This is why you open an engine that you intend to buy. That is the lesson .

ewww to my untrained eye that looks horrid [:'(] hope you get that fixed

104 @ 5:00pm today. Got my O.S FS .30 broke in though. Hopefully next week I can fly it after I get out of the hospital. lol

air tool oil yes , even marvel mystery air tool oil, not marvel mystery oil it has a cutting agent in it.

The engine is junk. The bearings arent just rusted, the front bearing is in little tiny pieces and there were balls just floating around in there. I have a webra 40 for 3 years now, and always used an after run oil of some sort. In winter, I plug the exhaust and carb after a good healthy dose of oil, and it has no corrosion. This is just unacceptable. I could see a bit of rust forming, but not to that extent. In manitoba, it is really humid.
I am also aware of Omega having after run oil (actually just rust inhibitors) that is what i run in my engines.
I bet that the engine was just run all season, then stashed away in a closet or shed for the winter.
Pilotfighter: The engine came with the plane, and two servos. I bought it for $20.00 (the guy really wanted to get rid of it) The way i see it, is im still ahead. I have a ST GS 40 that i got for xmas in it now. Its actually a pretty good combo.

HAHAHAHAHAHAHAHAHA It's 89 and 20% today. We have the Mexican Monsoon blowing through so it went up from our normal 6%. Can't hardly breath in all this mug!!! Should be blowing out this weekend though and back to the 6%.
To the OP, I have seen engines a lot worse then that after storage even with after run. Minn hit it dead on, it depends a lot on how and where it is stored. I just started using an engine I had stored but I stored it dry, I cleaned it with alcohol. Surprised me when I rolled it over and the bearings were grinding and stiff, I flushed it with Marvel Mystery Oil and it was just fine, just dry and really needed the lube.

ill still take it i love messing w/ picky engines trying to get them to work
just today i was messing w/ a old os 40 fp trying to get the dang thing to idle, took the entire thing apart, scrubbed for the better part of 3 hours, and now it will idle below 1/3 throttle [8D]

I have an OS 46SX that I bought in the late 80's or early 90's. It was used quite a bit when i first got it and it was even dunked in a seaplane crash (Engine sat submerged for about 15 minutes).

Then, the engine was retired for about 10 years and sat on a shelf in either a damp basement or a garage through extremely cold winters and humid summers.

Last year, I put it in my Northstar and it still screams.

This engine has never seen after run oil of any type, nor has it had any kind of special attention whatsoever.

And it's still ticking!

That engine isn't in bad shape at all. A new set of bearings can be had for about $20. Clean the rust off the crank shaft to prevent any rust from coming loose. Look closely at the cylinder sleeve and piston. if there isn't any scorng of either, it shoud be good to go. Or you can put a new piston, sleeve, and connecting rod in it.

The kind of rust you're seeing on that crank is not what one would see from a few weeks sitting in storage. That looks more like an engine that has been sitting for a few years in a humid environment. Under those conditions, even after run oil can be challenged. If the crank case is not closed off, moisture will build up due to temperature, pressure,and humidity changes.

Whatever you do, don't just pitch the engine out. Give it to someone that is willing to repair it.

Brad

I used to use after run oil...until I tore down an engine that, not as bad as these photos, was rusted....I stopped using after run oil and my engines run great......perhaps the folks you got this engine from didn't burn the fuel out at the end of the day

I don't burn fuel out either.

so is it better to let the engine run dry .. or kill it by fludding finger over muffler method ie more fuel/oil in the engine??

I think the key may be: use it or lose it.

I stopped using after run oil when I mounted one of my engines inverted and had a puddle in my workroom. No rust to be seen yet after several summers of abuse and winters in the basement. I do run omega with a dash of extra castor thrown in and try to burn out the residual fuel when done for the day.......

Ya know what we're learning in this thread?

For every guy you can find who swears that using (or not using) Product X will lead to lifetime success or instant failure, there's another guy who's had exactly the opposite results with it.

Been flying R/C since 1972 and have never used after run oil. I have never seen a rust problem with my engines. I get over 10 years out of my engines and fly a great deal. I never run them dry when I'm done flying.

Yup

I don't see after run oil hurting anything so I have always said if it makes you feel better using it then by all means use it. I was sent a big box of old two stroke engines from a friend that just ran them for a while then tossed them onto a bench, never ran them dry. His thinking was that the fuel evaporates and the castor oil stays until it hardens. When I need one of these engines I just heat them up until they roll over then take them apart and clean them to get rid of the old hardened castor. So far I haven't found any rusted bearings or cranks so there must be something to his thinking. I do use after run oil when I'm reassembling them, that or the Marvel Mystery Oil.
These engines were from Nothern Calif. and there is himidity, rain and snow but nothing like the mid west or the coast of Texas. I think humid regions of the country makes storage harder and I'm not exactly sure how I would go about it if I ever moved to the mid west? I store engines for a very long time, it could be years before I need one.