OK, What are the problems encountered when you disassemble a ringed engine? Specificly, does the Ring have to re-seat? I want to remove some varnish from my OS 50sx. How bout it?

ZB

I would not recommend to disassemble your engine. Clean the head and as much as you can around the top, but if you take the piston out the ring never going to seat properly again, unless you hone the cylinder and install a new ring and breaking the engine again.

I disagree. Just use caution when disassembling and reassembling to avoid scratching the ring or cylinder.
There is no reason the ring will not seat just as well after doing so. Use lots of oil when putting it back together. I am not aware of any way to hone the smaller cylinders anyway. If it's scored, buy a new sleeve and ring (piston too, if it's messy).
I do question why you would really need to disassemble to clean out varnish. If the whole engine is gummed up from sitting and won't free up with some solvent, only then I can see taking it apart. If it moves freely and runs fine, don't mess with it.

Some varnish might even be a good thing. (?) No metal to metal contact.

Jimmy,
Though you may be doing more harm than good, I have done it on a couple engines to change the bearings and it seemed to have little effect on them.

I do know that on a car, it is no - no. Also, if your model engine has any vertical scratches on the cylinder wall, your chances of screwing it up by removing the piston/ring are much greater.

Good luck,

Jim

OK, I'll leave it alone. It is a 50SX and it runs great, lots of varnish on the piston. Should I invest in a ring and cyl for the future? Will this one be around for a while?


ZB

I don't know the 50SX specifically but if you're not going to remove the ring from the piston then there's no problem. Just clean everything and put it back together. If the ring is pinned then make sure the gap is aligned with the pin before you try to reinstall the piston in the liner. If you've got varnish then one thing to check is that the small end of the rod is free to move on the gudgeon/wrist pin.

If you're going to remove the ring then do it a spiral. Lift one end free with your fingernail until it can just lay on the piston crown then slowly work the ring around and out of the groove so that the free end gradually moves across the crown. Refit in the same way. If the ring is pinned then check to see if the pin is centred in the groove (the ring can go on either way). If the pin isn't centred then it'll have a matching end gap so it can only go on one way. If the ring isn't pinned then they rotate slowly as the engine is running so it can be refitted any way you like.

I've found that a cleaned and reassembled ringed engine needs a couple of tanks of fuel before it regains it's seal and then it's as good as new.

If you are careful and do not mess with the ring and dislocate it, you do not need to worry.

The Varnish...

Forget it alltoghether.

If you said thick coal deposits in exhaust port and piston top, but varnish...

If you mess with your engine and remove the normal internal patina, you will just harm it.

You should not try to repair something that is not broken.

I know it is fun to dissassemble engines and loo at the cute connecting rods and pistons.

But frankly, unless your engine does not work, you should not dissassemble it.

Cheers,
Ikaros

Buy some liquid fuel injector cleaner. Put an ounce in a gallon of fuel. You should see a difference inside of the engine regarding cleanliness.

Clarence Lee of RCM's Engine Clinic mentioned this trick some years ago. Many have reported success. I have heard of no ill effects.

Well you guys have lost me on why simply taking a ringed engine apart and putting it back together would disrupt anything. Usually the sleeve is pinned so it can only be put back together one way. Even if it is not, the sleeve should be marked so it will go back in the same place.

On an automobile the rings are not usually pinned and are free to rotate. Why would disassembling that hurt anything?

Ernie

Hey Ernie ! Ive been a auto tech for over 20 yrs and torn down countess engines ! and I have never seen a rotating ring yet !! when assembling a ring set on a gas engine piston your to always stager the ring gaps so they are not inline ! if they are able to rotate there would certainly not be any good reason for stagering the gaps! you can see this prof of the rings not rotating by the ring marks in a cyl. just my $.02

At least in larger engines,(2-stroke dirt bike), I was taught to leave the varnished areas on the piston alone. These are low areas formed by heat cycling.

If your engine sags at high RPM this is a sign of varnish ( burnt castor oil) build up on piston & maybe sleeve. I find no problem with cleaning off . Use fine steel wool or Scotch-brite. This used to be a real problem with TD .049's & all castor fuel in my "olden days".
Downunder: I don't know what your Avitar is , but is a dead ringer for my mother in law.>>>>>>>>big max 1935>>>>>>>>

Rings are usually pinned in most Schneurle ported engines because the ports are so wide. In the older loop scavenged engines both the transfer and exhaust ports were segmented with 3 or 4 bridges to contain the rings. Simply by flicking one of these over for a few minutes you can watch the ring gap creeping around as the ring(s) rotated.

When assembling an auto engine it's just good practise to stagger the ring gaps to give the longest possible leakage path for the initial startup. After that, they'll rotate.

downunder: Didn't mean to insult your Avitar ! MAX H.

Briggs&Stratton built a test engine that you could see through the cyl wall while the engine was running, for that purpose. the rings never stopped rotating. Although I'm sure an engine with a cyl worn oval shaped with the rings worn to it would not rotate so I guess it depends on the circumstances.

If you have an engine you really like , I would start looking & buying some spare parts for it before they become impossible to find. Stash them away , if you do ever sell the engine you can always sell the parts. I try to keep gaskets ,wrist pin , rod & a ring if it uses one. Very seldom have needed a piston & sleeve, cranks I have straightened. My old favorite yet is my OS 40 FSR, rebuilt it twice now. Engines are like women , they are all good ,some are just better than others !! MAX H.

Yup! Some are better than others!

To my knowledge, all piston rings will rotate unless pinned. Especially in 2-strokes! If they didn't move what would be the point of pinning the ring? Because of this, there isn't much harm in taking apart a ringed engine as long as you don't stretch out the ring. If I'm not mistaken, the OS 50SX heli engine has a nickel plated cylinder just like their non-ringed airplane engines. This surface is very hard and, despite it's smoothness, doesn't require any scuffing or honing. A coarse scotchbright is usually all it takes to clean it up. After re-assembly one tank of fuel gets the ring back where it wants to be and you're ready to fly. At least that's been my experience.

big max...I didn't want to mention I know your mother in law

Sure am glad my wife don't get on here or I would be in deep s#&*. MAX H.

when the rings seat better is that were the increase rpm happens?????????????????

ok ZB,........ here it goes. the ring & piston should not be remove. unless you need to for dirt, (after bad crash,) or bearing replacement. the ring must seal against the cyl. wall, & must also seal against its bottom surface which meets the bottom of the ring land in the piston. as they wear together, they do develope very microscopic surface coatings of varnish. & as time goes on these are what all these parts seal against. if not in exess, theres nothing wrong with it. removal will affect the performace for a time after, till these coatings get regenerated. the ring's in engines do rotate as others have said, the pinning prevents the very edge of the ring from getting into a port & catching on it. the piston's running clearance in these ringed engines is a little bit looser than an abc engine, there the top of piston is what seals against the wall. less likely to mess up sealing surface in those engine's. the carb cleaner added to the fuel is the best thing to do. .......good luck with this either way you go.