hi all. i have an os 120 fs surpass non-pumped motor. apparently it is an older version with a choke flap (as per another member here, not my knowledge as i am very new to this aspect of the hobby)
I believe this plane sat for a while. I'm unaware if the engine was ran during the winter or if after run was used after its last flight. I was told it did fly last before the winter. My concern is that the prop is extremely hard to turn by hand. I have not tried with the electric starter yet. There is NO plug in the engine either so its not building compression. I belive there is an abnormal amount of constant resistance somewhere in the engine. There is "free" spin at all. Even if i try to snap the prop in either direction, it will only continue in its movement for a degree or 2 thats it. It won't even make 1/8th of revolution if you snap the prop. So I removed the head hoping that the problem was somewhere in the valve train, but its not. With the head off the engine, it still is extremely tight to turn. Once I removed the crank case cover, I noticed alot of what looks like rubber debris inside the case. Mostly behind the rod. Im unsure if it is rubber or not. Unfortunately I do not have the correct size tools to pull the cone and prop off, I will try to get them this week. That is my next move I think. Here are some pics of what I see. What are your thoughts? Where would you go with this?

If you can get all the rubber / plastic parts off the engine....dunk the engine in a tin can full of antifreeze and cook it for a couple hours on low. This should get the ball rolling to loosen things up while you wait on getting the prop driver removal tool.

Chevy, if you're going to post pictures directly from a server, please resize them to no larger than 800 pixels. At the size you are posting them, they are too big to fit the screen.

Ok. I'm sorry about that.
You have any thoughts on what I'm lookin at here. I've never heard of cooking an engine submerged in coolant before. I'm willing to try it though. I did manage to get the prop and all other parts off the front and is still very tight.

Slow cooking in green engine coolant is the gunge-removing zeitgeist.
You could try an auto-factors for a gallon of general purpose solvent.
That is normally a mix of Alcohol, Xylene and Toluene that should have a good go at getting rid of that castor varnish.
Even a week-long immersion in glow-fuel might loosen things up for you.

It's hard to tell from the photo, but the pile of rubber next to the rod could be what's left of the bearing retainer / shield?. Once you get it cleaned up, it will be obvious. There are several good tutorials about replacing bearings if it comes to that. You want to look at the piston / liner under magnification to see if the engine is worth messing with. The cost of these parts can make doing a rebuild not practical.

Like pig said, it's hard to tell from the photos but it doesn't look like the engine was run all that much but it does look like castor gunk. Have you tried just heating up the engine with a covering heat gun and rolling it over? The heat will sort of melt the castor gunk and free it up. If that works then you can just heat it up again and flush it with alcohol, use a little oil on the moving parts and fire it up. Just make sure there is no floating junk inside the engine. At $400.00 bucks for a 1.20 these days it's worth every Penny to rebuild them. I have a good little book on rebuilding the OS four strokes if you want the name, I think it is still published.
Gene

Cool thanks for the insight. Yeah I will take the name of that book. Any all info is the best tool to have. We all start somewhere right!
Thanks again

Hi!
The pictures tell the story! Rust ,rust and lots of rost!
Change ball bearings!!!! This is easy to do!

I do appreciate your reply, however, wouldn't a bad bearing have some sort of play or rough pebbly feeling while in motion? This unit is just super tight. As I rotated the prop, it was smooth and crunch free. Just real tight.

It's all just conjecture, especially from here where I sit. For all we know this engine just needs a good cleaning....but.... That does look like a pretty hefty pile of something laying there where the rod and crankpin meet [:-]. Really do a good job of assessing all the parts and checking fits, roundnesses, look for gouges, etc. Then tally up the replacement parts cost. OS has reasonable prices on some repair parts if they still carry parts for your engine.
Some guys don't care about the cost so much, they just like rebuilding engines.

I would remove any and all debris, then douse it with fuel and see if it loosens up. If not, try GrayBeard's heat suggestion or a combination of the two

If your bearings are gunked up with old castor there may not be any play, they would be very tight. I just had to replace bearings in one of my .91s. The engine was given to me, it ran great but I could hear and feel the bearings. I use the engine anyway until one day I could hear the bearings in a fly by, that's loud!! When I opened up the engine the bearings didn't show any real signs of wear or being loose. That was the problem, just too much nasty old castor oil that was making them tight. RC-bearings.com and a couple hours of work and the engine is like new again. However, you can't just tell by looking. Once the engine is loosened up and run a little it will tell you what it needs, if anything. My first four stroke book was from RC Modeler magazines anthology library series. RCM is defunct but they still sell plans so perhaps there library is still going too?? You will have to do the google and check. The title is, A guide to O.S. Model 4/Strokes by Graham C. Rice. It's a very good, easy to read and understand book with good pictures. I even use it today on every rebuild. At this point I would just heat and loosen to see if there is any problem? No reason to go looking for trouble, it will tell you when you fire it up. Stock OS bearings are pretty loose when brand new in the older engines. You can also soak an engine in some fuel to loosen things up but I like to heat them up first.

Hi!
All of us that has seen a experienced old gunky Castor oil clad engine bearings know that this is the fault!
Just take the engine apart and get rid of those nasty bearings! It's so easy to do! Cleaning is no option when it looks so bad as it does in the pictures.

What's happening when you turn the crankshaft now is that the balls in the ball bearing stand still and the axle glides only on the inner ring surface, or try to glide on the inner ball bearing surface (Which it cannot do due to all that old gunky Castor oil)!

thanks everybody, the engine free'd up. i soaked it in a tub of hot used tranny fluid. that seemed to do the trick. the main problem was with the wrist pin. it was a complete pain to pull the piston/rod out because of the rod not wanting to slide on the pin. i git it out soaked it all and the gunk pretty much fell off. the engine looks really good and clean. sprayed it all out with high pressure brake clean to free up any stuck contaminants. put it all back together with some mystery oil and she freely spins over by hand. will find out soon once i get some fuel and a couple plugs if she fires.

thanks again

Now that the engine is flushed out and loose, grab the prop and forcefully try to rock the crankshaft as you check for slop.

I don't mean end play,[some end play is acceptable] but axial play. You don't want to feel any. Sometimes this shows up after an engine has been taken out of mothballs and run for awhile.

.
did you set the timeing correctly? when the piston is at the top of the exhaust/intake stroke neither valve should move, if one does its not set right, you said you were new so im just wondering. some the looks of it you know what you are doing, just dont want you to trash the engine.

Yes sir. I still need to check/adjust the valve clearence. I just forgot my feeler gauges at my shop. I'll bring them home when I'm ready to fire it up.