Anyone know why 2cycle's don't have rings?

[olds97_lss]

I was just thumbing through an older rc mag and they had a breakdown of 2 cycle vs 4 cycle nitro engines. I already know how they work, used to work on 1:1 10 years ago or so and have rebuilt many of both. But in the RC world, I always thought it is kind of stupid that the engines don't used ringed pistons.

Anyone know a real reason why? Is it just because of the high rpm's or what?

Or is this like my questioning the use of a collet vs a keyed shaft on the crank shafts... no one cares

 

[vbgagnon]

I think the rings are so the oil doesn't get burned up(I think?) Where as the 2cycle has the oil in the gas and needs to coat the engine. I could be way off, but at least thats what I think.

 

[olds97_lss]

Ummmm... what?

2 cycles with rings are in the 1:1 world and some run without any oil in the crank case. Look at chain saws, weed eaters, zenoa rc engines. They all run with gasoline/oil mix in the oil and no oil in the crank case, but they all have pistons with rings.

The only differance with our little rc 2 cycles is that we run nitro methane with oil and the cylinder is cone shaped to create compression. As the engine heats, the cone becomes less of a cone, but still a cone so that the piston makes (or almost makes) contact with the sidewall of the cylinder while being constantly coated with fuel/oil that we run in them.

If it had anything to do with the fuel, then why is the 4-cycle rc fuel so similar if not the same?

 

[mr_bob]

I think the reason why we dont have rings is b/c in a 1:1 car you dont have a hole the piston has to pass and they have valves that sit on top of the piston to let air in and out

and in our engines we have the exhast port to worry about when the piston makes a turn


please tell me that made sense please

 

[olds97_lss]

Not on a 2cycle 1:1 engine you don't. It operates in pretty much the same fashion as these do, just a lower RPM. I have seen reed valves on my old yamaha motorcyce that would let air/fuel in from the carb, but wouldn't let the air/fuel flow back out. It was kind of like a one-way valve.

I wonder what RPM a weed wacker engine runs...

 

[lykan]

Weed whackers do a ton of RPM.. I was thinking of making a low power out board with a engine i picked up. Unfortunetaly they have to get going way up in the RPM to get any power, by then they are way to loud.

The only real reason I can guess at would be simplicity and cost? It seems that rings in the 1:1 world are pretty tight tolerance. Would the tolerances for Nitro's have to be as tight as the 1:1's.. if so it would mean some gnat's ass rings lol...

If you think of the brass/soft metals they use in RC's it seems to be oriented to the cheap side of things. It's just one more component.. I can imagine the cost of a nice nitro with rings, and a hard sleeve with tight tolerances...

Just ideas.. I'm no expert lol

 

[scottm]

The only reason nitro car engines don't have rings is because of the rpm they turn - 30-40,000. 2 stroke nitro plane engines have rings but they only turn 12-14,000. It has to do with a piston not being able to survive a ring beating back and forth in the groove 600+ times per second. Steve Pond on radiocontrolzone.com explains it.

 

[Rolex]

Some airplane 2 stroke engines are ringed, and some are not. Same goes for the 4 stroke. It's what you pay for.
Ringed engines also need a much longer, and more precise break in period.

 

[cbreaker]

I believe the small nitro engines don't have rings because they are too small for rings, the compression is too high, and they'd wear out way too fast. They are super high RPM and the rings would crumble.

The precise machine work of the piston/sleeve/no ring design allows for a lot of abuse.

 

[olds97_lss]

That's kind of what I figured. To small, to many rpm's, too much abuse.