One ring vs Two rings on 2 stroke chainsaws

[timberwolf]

I think you see single rings less in bigger saws due to lower RPM. Sort of general rule of thumb is that rings do little of the actuall sealing at over 8000 RPM. It's at speeds below 8,000 the sealing of the extra ring really shows up.

I have a few big race saw pistons though with single rings, but for that application were working in the cut well over 8,000.

Second ring also helps some with cooling getting the heat out of the piston to the cylinder wall.

 

[edisto]

Give me a longer rod.

One overlooked function of the rings is that they transfer heat from the piston to the cylinder, which is an additional factor that might explain why bigger 2-strokes have them.

An overlooked advantage to having a single ring would be the potential to use a longer connecting rod by moving the pin bore up. In fact, there seems to be a lot of wasted space above the single rings, so i don't think the potential for longer rods (stop giggling when I say longer rod) is not being utilized.

 

[04ultra]

I think and someone will have to verify that Husky also make 1 ring conversions. My 372xp is 1 ring. It was rebuilt at a Husky dealer this way.

I have a few of them here on the shelf ........

 

[brinkwolf]

Sorry but I don't think the heat issue is the reason. Especialy since as said earlier that 125cc to 175cc 2 stroke motorcycles engines don't need two rings. 125cc is alot bigger than most saws.

 

[Lakeside53]

There are several lengthy threads on this this already. One no so long ago... many external links on engine design theory have been referenced.

A few of the bottom lines...

1) 1 or two ring: The plated bores don't wear materially for the life of the engine.

2) For the same size and tension, 1 ring will wear faster then 2 rings.

3) The primary transfer of heat from the piston to the cylinder is through the rings.

4) Wider rings, and more rings, equals more friction but vastly offset by better heat transfer. Reality is though.. there is only a quantifiable amount of heat to remove for a given engine power, so at some point more or wider is irrelevent and will work against you.

5) Except in continuous power devices (ex. backpack blowers) where a great deal more heat is generated than in an "intermittent use" devices (ex. chainsaw), most MODERN 2 ring chainsaw pistons use 2 x 1.2mm rings.

6) The top ring wears way faster then the bottom ring. In a single ring engine, you don't have the second...


Observations:

Compariing trail bikes etc is invalid - their ring life time is measured in 10's to low hundreds of hours. Chainsaws (ex. stihl pro) are 2500 plus.

Chainsaws : for a chainsaws used in milling, I'd be putting in two fat rings on my 066 instead of 2 skinny... Not so much about ring life, but heat transfer.


Now.. use search and see the hundreds of posts on this topicopcorn:

 

[Lakeside53]

I think and someone will have to verify that Husky also make 1 ring conversions. My 372xp is 1 ring. It was rebuilt at a Husky dealer this way.

The 2 rings Husky's were to pass EPA a few years back. Interesting, that that make it harder to pass the 2010 emissons due to the tiny amount of unburnt trapped between the rings... The single ring pistons are still available.

 

[Crofter]

I would like to see it explained how the rings stabilize the piston since they are free to slide in the grooves and the depth of the ring is less than the groove depth. I only see the ring as being able to receive or exert force up or down not laterally.

 

[timberwolf]

Fat rings are good in some ways like wear and heat transfer but they are hefty and don't like high RPM. Even a 1.5mm ring is a problem if you want to make a high RPM saw.

 

[brinkwolf]

Huh, Andy have you ever been to a motocross race? You want to talk about Screaming 2 stroke engines. And who said anything about a low rpm trail bike.

And so if the first ring in a two ring set-up fails first, then it doesn't matter how many rings you have. Were is the pieces of that failed ring going to go? Sounds like a scored piston and cylinder to me.

 

[brinkwolf]

I would like to see it explained how the rings stabilize the piston since they are free to slide in the grooves and the depth of the ring is less than the groove depth. I only see the ring as being able to receive or exert force up or down not laterally.

Why do you think you have to compress them when you install them. And if the ring fits the groove right then you wont have so much slack.

 

[brinkwolf]

Oh and I'm sorry for bringing up what must be a sore subject again. I didn't bother searching to see if this has ever been posted before. And I still haven't got but maybe a half way good answer to this subject. Funny it sure seems to come up all the time when these to big brands are compared.

 

[Lakeside53]

Huh, Andy have you ever been to a motocross race? You want to talk about Screaming 2 stroke engines. And who said anything about a low rpm trail bike.

And so if the first ring in a two ring set-up fails first, then it doesn't matter how many rings you have. Were is the pieces of that failed ring going to go? Sounds like a scored piston and cylinder to me.

Why do I get the feeliing you're just trolling?


I have no idea what you talking about in your first statement. Motocross? oh.. a "few"... I'll stand by mine and say your expected lifetime is very low.

In your second... chainsaw rings rarely 'fail" by breaking They just wear out; the ring gap gets wide and the tension is lost. It's common to see a top ring with an end gap 3-4X the second ring.

 

[Crofter]

Why do you think you have to compress them when you install them. And if the ring fits the groove right then you wont have so much slack.

When you compress a ring you are not forcing it against the piston! you have to apply force to compress the ring to fit it into the bore even without a piston. That force is absorbed within the body of the ring itself.

While it does transfer its compressive force to the bore, it has only sliding contact with the ring lands. Gas forces can act in addition to the rings own expansion forces but the gas pressure is evenly distributed between the ring and the piston and does nothing to stabilize anything any more than the air on all sides of your body helps to keep you standing upright.

To add lateral stability takes lateral force and since the ring is free to slide laterally in the grooves it cannot transfer force in that direction.

Brinkwolf, I referred to ring groove depth being greater than ring. That is not reference to groove width. This is not "slack" but intenionally so since the rings are not designed to absorb the piston thrust forces due to rod angularity.. Rings are not there to stabilize loose pistons!

 

[brinkwolf]

Why do I get the feeliing you're just trolling?


I have no idea what you talking about in your first statement. Motocross? oh.. a "few"... I'll stand by mine and say your expected lifetime is very low.

In your second... chainsaw rings rarely 'fail" by breaking They just wear out; the ring gap gets wide and the tension is lost. It's common to see a top ring with an end gap 3-4X the second ring.

Nah I prefer to cast rather than troll. Just ask the bike mechanic that posted earlier about life on motocross motorcycle engines(you may be suprised if you haven't owned one).

 

[04ultra]

Oh and I'm sorry for bringing up what must be a sore subject again. I didn't bother searching to see if this has ever been posted before. And I still haven't got but maybe a half way good answer to this subject. Funny it sure seems to come up all the time when these to big brands are compared.

Read post 18 ............Why a sore subject??.........Because Husky is using 2 rings on the big new modern saws?????opcorn: opcorn:



.

 

[Lakeside53]

Nah I prefer to cast rather than troll. Just ask the bike mechanic that posted earlier about life on motocross motorcycle engines(you may be suprised if you haven't owned one).

lolol I help a couple of racers change their ring about ever 60-80 hours.. and they think they are really pushing it. Judging from the end gap and edge wear, they are...:greenchainsaw:


i guess you haven't worked on too many saws or bikes then?

 

[brinkwolf]

When you compress a ring you are not forcing it against the piston! you have to apply force to compress the ring to fit it into the bore even without a piston. That force is absorbed within the body of the ring itself.

While it does transfer its compressive force to the bore, it has only sliding contact with the ring lands. Gas forces can act in addition to the rings own expansion forces but the gas pressure is evenly distributed between the ring and the piston and does nothing to stabilize anything any more than the air on all sides of your body helps to keep you standing upright.

To add lateral stability takes lateral force and since the ring is free to slide laterally in the grooves it cannot transfer force in that direction.

You ever hear a term called Piston slap? It's a real common problem in Drag Racing. The rings are what keep the piston true to the bore. Take them out and that piston will nock around like crazy.

 

[brinkwolf]

lolol I help a couple of racers change their ring about ever 60-80 hours.. and they think they are really pushing it. Judging from the end gap and edge wear, they are...:greenchainsaw:


i guess you haven't worked on too many saws or bikes then?

Saws not really(is why I'm here dude) bikes a few back when I was into motocross. I just wanted to here peoples ideas not get into a pissing contest.

 

[04ultra]

You ever hear a term called Piston slap? It's a real common problem in Drag Racing. The rings are what keep the piston true to the bore. Take them out and that piston will nock around like crazy.

Will it even run with out rings ??? opcorn: opcorn:

 

[Lakeside53]

You ever hear a term called Piston slap? It's a real common problem in Drag Racing. The rings are what keep the piston true to the bore. Take them out and that piston will nock around like crazy.

It's a real problem in chainsaws also, but two verses one doesn't have any material effect. The skirt contacts the bore in either case.