Well I decided to take the motor apart for a good cleaning since it seen a good 5 gal allready. Ive read that its good to mark the con-rod so you can put it back in the way it came out. After the motor is fully disassembled it dawned on me that I missed that step.
My question is, how important is the orinatation of the Con-Rod? Ive rebuilt plenty of car motors, but this is my first major overhaul on a larger size plane motor. OS 60fx to be exact. Any help will be very much appreiated.

You can usually tell which side was facing the backplate because it will be polished and have some light scratch marks on it. If you still can't tell, then I guess all you can do is guess.

Joel

Nathan:

The mistake was taking the engine apart when it didn't have anything wrong with it.

Not just the con rod, it wants to be in the original position due to the matching wear on the rod and the crank pin, but also the piston and liner wear one to match the other. You will never get them back in the exact position, they will have accelerated wear now until they reseat.

Just do your best to get it back as original, and hope the reseating doesn't take all the wear remaining in the piston and liner's life.

Bill.

If you look at the rod bearing that goes on the crank shaft it usually has a chamfer on one end of the bearing bushing hole. This chamfer is to clear the small radius in the corner of the crank pin where it meets the counterbalance. So the chamfer faces the front of the engine. If the rod/piston is assembled the wrong way round it is possible for the rod to sieze or wear material away at this point.

Ed S

It's not necessary to take an engine apart to clean. Just soak it in a tub of denatured alcohol, or a hot crockpot full of antifreeze.

As others have pointed out, it's rarely necessary to disassemble your motor....especially one
that is running well.

It's just too easy to damage gaskets and O-rings, upset wear established wear patterns and what
have you.

All too often, the result is a very clean motor that doesn't run as well as it did before it was needlessly
dismantled...if it runs at all.

As a kid, I think I tore apart my motors daily. No wonder they ran like garbage back then.

Live and learn!

You don't take apart your car engine for routine cleaning...don't do it to your model engine either unless
ABSOLUTELY necessary.

Simply wipe it clean at the end of a flying session...put a little oil in the intake and your motor will look nice and run
well for many years.

Regards,

Race

All of the replies advising one not to disassemble and engine are quite valid.

However, Too late folks. "rcfury" has his in pieces already.

Ed S

Yeah i can agree i shouldnt' have taken it apart. The story was I was flying the other day and the stupid carb retainer screws vibrated loose and off comes the carb. The motor then flames out and I go in for a not so good landing. It touched down in some really tall grass. When i come to inspect the damange (none was done) but grass and dirt coated the motor. Not knowing if anything got in it, I thought it would be safer than sorry and give it a good cleaning.
I took off the head the top of the piston and the head had a huge about of carbon all over it. Running it a little to lean.
oh well the damage was allready down so put it back together after a good soak in the anti-freeze.

-Thanks for the tips none the less.

OK, how about the same question but this time with a ringed-engine, OS .50SX? Is it just a crucial for this engine as it is for an non-ringed engine to get the connecting rod in the same direction?

And I needed to take this engine apart because the heavy varnish on it was unusual for a low-time engine. I run WildCat 15%. When I removed the head I noticed the varnish was also present under the head -- it seams this engine has been leaking from the top. Now that I recall, the head bolts and backplate bolts came off without the normal starting snap -- they must have been loose.

Jim:

Anything that rubs in its operation will wear, and original orientation should be maintained.

In ither words, yes, put the rod, piston, tappets, rockers, valves, push rods, everything back in its original position. This is especially true concerning the tappets, their rubbing contact on the cam lobes is the most highly loaded rubbing contact in the engine. Second highest is the con rod on the crank pin.

Bill.

If the same conditions exist, then for the reasons I stated, Yes.

Ed S

Jim, it is very important with the .50sx that the piston gets put on the crank with the camfer on the front. This is a ringed engine, and the gap on the ring will fall in a different spot if you rotated the piston.

Please explain what you mean by "camfer on the front". Is there some way for me to tell which direction the rod is connected, like maybe a tell-tail wear mark on the lining where the ring gap is?

I will hold off re-assembling the engine until I am convinced I have it correct -- this is a fantastic running engine and the only complaint I had was how quickly it became varnished-up.

Hope you can understand my super-duper drawing and above average handwriting.

That picture should explain it just fine.

That picture actually solved all my problems. As we speak my motor is taking a "methanol" bath right now.. IM going to let it soak for a few then put it back together. Granted I made the mistake and hopefully I didn't distroy my motor. But, i have a saito .56 on the way which is going into the plane anyway.

Jim, this seems unusual...I just took the back plate off my 50SX the other day and I was shocked at how BRIGHT it was inside (I also use Wildcat/Hobbytown...10%...cas/syn w/ extra oil added to get up to 20%). About a year ago I installed high speed high heat bearings, so no rust.??....Dave


I will hold off re-assembling the engine until I am convinced I have it correct -- this is a fantastic running engine and the only complaint I had was how quickly it became varnished-up.

Inside was nice and clean and bright, except the carbon on the piston head and heat stains on the liner and piston.

There was a considerably amount of varnish all over the top of the head and under the head where it mates to the crank. I also notices rust on the surface ring of the rear bearing, but not the bearings themselves.

Hilleyja

I've noticed the same with my 50SX but have not determined exactly what is causing it. I had it in a 40 size SU31 where the instructions and nock off ARF instructions of the same plane really said nothing of how the ventalation for the engine was set. 3 other guys with the same kit all noticed over heating and plenty of buildup all around the head, loose heads etc.
Plus the factory silencer tends to leak a lot so I suspect there is plenty of wait oil to bake on to the engine. Two of us also had to make adjustments to the mixture running a little lean kicking out fuel from the carb which should happen.

Check if any of this happens with the engine when you get it back together and make the necessary adjustments. Once done it shouldn't run too hot nor spill a lot of fuel to bake on the engine so quickly.

Oh and Yes the camfer goes up front. When ever taking an engine apart sketch these subtle parts down or even mark one side with perminent marker so you don't forget which way to put it back together. The marker can be rubbed off once you have it back together or is generally harmless.

Well, I am now in the position where the title of this Subject definitely describes my result of taking apart my OS .50SX. I found out the hard way that you do not re-insert a ringed-piston into a steel liner with a rubber mallet -- scratch one piston and ring assembly.

Having said that and subsequent to ordering a replacement piston/ring assembly from Tower Hobbies, how does one re-insert a ringed piston?

Note: I tried to compress the ring with my fingers enough to smoothly insert the assembly into the liner with the liner removed from the crank -- I could not figure out how to do that. I did note that the liner is beveled on the bottom and tried to insert the piston/ring assembly from the bottom -- I could not figure out how to do that either and in this case was unable to compress the ring at all.

What's the secret here?

BTW, does anyone have a source for piston rings other than Tower -- they want a rediculous $19.99 just for the ring? If I have to pay $28.99 plus $19.99 for a piston/ring assembly then I'm thinking this engine becomes a parts engine.

Jim, do a search here for Frank Bowman. He has rings for any make or model. You would be well advised to send the engine out to him and he probably can repair your piston and install a new ring...that's what he did for me and many others. Also he's so reasonable you won't believe it....Dave

Jim,

You need to rotate the ring so that the gap lines up with a small pin on the piston. Once you have it lined up, you can squeeze the ring and slide it up through the bottom of the sleeve. Its a little tricky, but possible. The next trick is to get the piston con rod on the crank. Take your time, and you will figure it out. Getting the piston on the sleeve is the tough part.