Why no rings on piston in RC engine ?

[Captain Chaos]

Why not run rings on the piston.Would it not be much cheaper to drop in a set of rings ever other weekend than having to replace the entire piston and sleeve every few gallons? I can burn a gallon in a weekend of practice.How many gallons are you guys getting out of the small blocks for off road like the 3.3?

Its probably a dumb question but this is how I use to freshen up my KX motor when I raced moto X.

 

[RC Addict]

I would thing for the same reason diesel engines use sleeves--the pressure would blow the rings right off?

 

[destrucktomaxx]

Nitro engines aren't ringed because its less complicated. Piston rings mean more slop in a rotating assembly and while they seal well, they don't seal as well as a precision fit. Diesel engines use cylinder liners because of the durability and ease/cost of replacement. You can sleeve an block hundreds of times where you can only machine it once or twice.

 

[olds97_lss]

I think RPM plays a role as well. Considering RC nitro engines are designed to hit 40K RPM's, it would be tough to get a ring to stand up to that kind of torture for very long. Some of the larger 4-cycle nitro engines run rings, but their RPM's are way lower.

 

[RC Addict]

I think RPM plays a role as well. Considering RC nitro engines are designed to hit 40K RPM's, it would be tough to get a ring to stand up to that kind of torture for very long. Some of the larger 4-cycle nitro engines run rings, but their RPM's are way lower.

That HAS to be it. I didn't think about the high RPM's. Good catch, olds!

 

[destrucktomaxx]

I think RPM plays a role as well. Considering RC nitro engines are designed to hit 40K RPM's, it would be tough to get a ring to stand up to that kind of torture for very long. Some of the larger 4-cycle nitro engines run rings, but their RPM's are way lower.

Exactly my point. Imagine the side thrust load on the piston in a TRX 3.3 at WOT...I'd reckon it could rival a 1:1 engine in that aspect.

Information about Nitro Engines

 

[charliejp]

Just curious myself. Would the temps and size have anything to do with it? I these engines ran rings they would be very small.

 

[frickenjoey]

Actually some do run rings. But they are all airplane engines as far as I know. There are two types of rings in nitro engines, DYKE'S and CONVENTIONAL
A DYKE'S type ring is a "L" shaped ring that fits at the very top edge of the piston. Many people can not even see it as there is no piston material above it. Dyke's rings do not feel like they are working (no compression) when the engine is turned over by hand. A dyke's type ring is pressure activated, (it is like a dyke) when pressure pushes against the inner side of the ring it is pushed out tightly to the cylinder wall. When it is running past the ports no pressure is pushing it so there is less friction. This is why dyke's rings produce more power than conventional type rings.

A conventional ring is just that. It has a rectangular profile and fits into a groove usually about a 1/16" down from the top of the piston. Conventional rings, when broken in properly, provide a good seal at any speed. Conventional rings have constant tension that force them against the cylinder. When you flip a good conventional ringed engine over it feels great with snappy compression. Now with that being said, I have to say that Olds is spot on with his answer. An aircraft engine will only turn 15K at its max RPM. That is not even half of most RC vehicle engines.