One Ring or Two?

[eiklj]

Just a quick question, not trying to start a war. (Husky vs. Stihl vs. Whatever.)
I am curious to learn why some manufacturers use 1 piston ring while others have 2.
I've heard 2 is more stable.
I've heard 1 allows higher revs.
This would apply to all 2 strokes, not just chainsaws.
Just wanting to learn. Thanks.
je

 

[blsnelling]

When I port a saw with two rings, it goes back together with one. There almost no affect on compression, and it can make a difference of a few hundred RPMs in the cut, due to less drag.

 

[w8ye]

On most of the Husky's from the factory, the single ring pistons had a thicker ring than the two rings on a EPA 2 ring piston.

 

[rob066]

It is said that two rings transfer more heat to the cylinder wall. I personally dont see any difference. To me one ring lasts as long as two.

 

[SawTroll]

The second ring doesn't work properly anyway, because it isn't in contact with the compression pressure. It just adds some friction, for no good purpose.

At least that is how I understand it.

 

[HELSEL]

When I port a saw with two rings, it goes back together with one. There almost no affect on compression, and it can make a difference of a few hundred RPMs in the cut, due to less drag.

What do you do with the ring groove
that isn't being used?

 

[hangfirew8]

The second ring doesn't work properly anyway, because it isn't in contact with the compression pressure. It just adds some friction, for no good purpose.

At least that is how I understand it.

The purpose of the second ring is supposed to be to reduce or eliminate piston contact with the cylinder wall.

I won't get into the debate of whether that is a worthwhile goal or not. Just keep in mind when altering a design from one to the other that the original designers made assumptions about lubrication, clearance, etc. based on the original format.

HF

 

[blsnelling]

What do you do with the ring groove
that isn't being used?

Well, I've heard that it could be filled with a ring from a smaller piston, but I simply leave them empty.

 

[HELSEL]

Well, I've heard that it could be filled with a ring from a smaller piston, but I simply leave them empty.

Yes putting a smaller ring on or pinning
it on both sides of the intake illuminates
a lot of spit back though the carb. You will
notice it more with saw not running a breather.

 

[sefh3]

Also make sure it's the top ring left in not the bottom.

 

[husqvarnaguy]

The man I learned from said one ring is better. Higher revs and less friction.

 

[Andyshine77]

Like most I prefer one ring for all out performance. When it comes to a real work saw I like using all of the OEM parts that came with the saw. One has to ask the question, is 300 rpm worth the risk of a possible serous and premature failure? I personally don't like the idea of running one ring, on a two ring piston. Piston stability would be my main concern, along with possible buildup in the ring groove. I could be way off here, as I'm far from an expert.

 

[Tzed250]

Not again...

 

[Chris-PA]

One ring to rule them all..........

 

[A.E. Metal Werx]

Pp655bp

Ive been having a hard time deciding weather to single ring my PP655BP or run both rings.. My question about the single vs dual rings is... Does the size of the piston make a difference? Run a single ring say up to an 80ish cc saw and use both rings or everything larger? Or does size make no difference?

 

[blsnelling]

Like most I prefer one ring for all out performance. When it comes to a real work saw I like using all of the OEM parts that came with the saw. One has to ask the question, is 300 rpm worth the risk of a possible serous and premature failure? I personally don't like the idea of running one ring, on a two ring piston. Piston stability would be my main concern, along with possible buildup in the ring groove. I could be way off here, as I'm far from an expert.

I don't think a single ring in a double ring piston would be any less stable than a single ring in a single ring piston.

 

[w8ye]

For a Husqvarna 372, the Meteor replacement piston is single ring.

 

[eiklj]

Thanks for all the good feedback and information shared here. I appreciate it.

I thought maybe a long stroke or crank throw required 2 because of the greater crank/rod/piston angles seen in larger engines. Although I've seen plenty of short stroke, small bore engines with 2 rings.

I also wondered if 1 ring equals lower manufacturing costs, not to say 1 ring engines are cheap or of lesser quality.

I believe Remington used 3 rings on some models, but not sure why. Maybe that was the design standards of those days.

I suppose todays engine designers walk a fine line between durability, manufacturability, and profitability when creating products.

 

[Tzed250]

Some 250MX bikes have a single ring, but they are liquid cooled.

 

[adam32]

I like two thin ones or one regular... :msp_thumbup: