<div style="margin: 0in 0in 0pt"><span style="font-size: 10pt">Hello all
I have seen most engines use 3 rings on the piston while most of the model 4 cycle engines such as Saito and OS use only one piston ring.</span></div><div style="margin: 0in 0in 0pt"><span style="font-size: 10pt">What is the main purpose of using a single ring on these engines? Also what is advantage and disadvantage of multiple ring vs single ring</span></div><div style="margin: 0in 0in 0pt"></div><div style="margin: 0in 0in 0pt"></div><div style="margin: 0in 0in 0pt"><span style="font-size: 10pt">Thanks</span></div><div style="margin: 0in 0in 0pt"><span style="font-size: 10pt">Borna</span></div>

single ring has less friction and drag,

Four stroke model engines use piston blowby to oil the lower end

<p style="MARGIN: 0in 0in 0pt" class="MsoNormal"><span style="FONT-SIZE: 10pt; FONT-FAMILY: Arial">Thanks for the answer. Obviously sing ring has less friction but that doesn’t tell the main purpose these engine use single ring is friction .

</p></span></p><p style="MARGIN: 0in 0in 0pt" class="MsoNormal"><span style="FONT-SIZE: 10pt; FONT-FAMILY: Arial">Also if there is enough blow-by exist to lubricate the lower part of cylinder engine, then don’t you think the engine will suffer a great deal of compression.



Borna</p></span></p>

When you compare the 4 stroke engine in a car to a 4 stroke in a model airplane you must consider that the oil is in the fuel and must be blown through the engine in an airplane. In a car engine it is separate and is circualated by a pump. The oil itself also helps add compression to a model airplane engine.

Of the three rings in most full-size piston engines, the top-most is the compression ring. The one below it is the scraper ring (for scraping the oil off the cylinder walls) and the bottom ring is the oil-control ring.

With model engines not having an independent oil system, the bottom two rings are not needed.


Some model engines do have two compression rings, but they are real vintage stuff.

Dar, nice answer. 

Did anyone also tell him that there is a large gap between ends of the ring to allow a lot of blow by.  And that it is smart on a new engine to dribble some oil on the rocker arms and down the push rod tubes berfore firing up for the first time.  A little oil dribbled into the cylinder head also helps.  Bearings are usually prelubed and that lube will be eventually washed out by the blow by oil in the bottom of the crankcase.

Any way, have a good day.

Cheers,

Chip

Dar, funny answer... In the model engine with 2 ring are compression very difference from the model engine with 1 compression ring, also much less leakage. My model 2 stroke engine has 2 ring and keep copression much better than 1 ring when i am holding the propeller with the piston near TDC without great loss of compression. It took much longer time to get loss of compression.

It will be bad idea to use 2 ring in 4 stroke engine who are running without own oil to lubricate the engine, the 4 stroke engine has larger air mass to take in the cylinder enough to keep enough compression in short time + a big ring gap to allow oil from fuel to go through ring gap and give lube to moving parts below piston.

I am working as car mechanic for Peugeot dealer, Most automotive pistons have three rings: The top two while also controlling oil are primarily for compression sealing (compression rings); the lower ring is for controlling the supply of oil to the liner which lubricates the piston skirt and the compression rings (oil control rings).

In older 2 stroke dieselengine has 3-4 compression ring and 1 ring in lower part of piston below wrist piston for improved crankcase compression.

Here're a few engines with two rings.

David

Lots of gasoline powered model engines come with 2 rings. So do lawn mowers and hand held power equipment such as weed eaters and chainsaws.

Quote:

ORIGINAL: Rcpilot

Quote:

ORIGINAL: DarZeelon

Some model engines do have two compression rings, but they are real vintage stuff.

Lots of gasoline powered model engines come with 2 rings. So do lawn mowers and hand held power equipment such as weed eaters and chainsaws.

In my remark above, I was referring only to model glow engines.

You are right. Many late model gasoline engines for models do have two compression rings.
I was not referring to that type of engine, however.

Yes.

Bill

Agreed.

Bill