2 ring piston ?

[Crofter]

Ben how about some sources for the things you say with such certainty. Opinions should be formed on a concensus of information. Being a little less overbearing might actually increase ones credibilty. Dont be so quick to state that anyone who holds a different opinion than yours is the moron like you state in your previous post. Come on now, lighten up and provide information and allow us the right to form our opinions based on everyones information.

 

[Crofter]

Spacemule, as you know I have played around with the model airplanes and ringless is the norm there. Of course the breakin procedure is quite important and they work in a normally clean air inside and unlimited cooling outside. Dont know if they would have the flexibility to work in a saw.
The cheap throw away saws and power equipment use a lot of one ring designs to reduce parts count and cost. They lend a bad rep to one ring that may be attributed to other things. On the other hand some competition engines that are working on the very edge of maximum piston speed, use but one ring, because they live where a two ring piston would see failure. Under such conditions, good sealing and ring stability is more predictable with a single ring. Undoubtedly such an engine will not have the longevity that a lower stress application will. I would like to hear the experience of real world saw techs to see of there is any overwhelming evidence that one system is greatly superior to the other.

 

[rahtreelimbs]

FWIW some of the baddest modded saws have 1-ring pistons. Would anyone let thos issue of one ring sway their decision on a saw purchase?

 

[stihltech]

ringy dingy

Stihl has done it both ways, but they used thicker rings than Husky in earlier saws, can't say for sure about the latest models.
There is one thing for sure, the cleaner the air filter, the longer ANY ring set up will last. Some times I think all this debating is trying to blame the saw, ANY saw, for something that proper maintenance would have prevented.

 

[Lawn Masters]

Your signature says it all Stihltech, any saw is only as good as the maintenance it recieves.

 

[bwalker]

Frank, I am not going to dig through engineering texts to prove a point.


I guess what I am getting at is the husky rep would probly be saying two rings are better than gold if husky had all two ring motors.

As for the model engines. Arent the bores tapered with the ringless designs?

Rich, The baddest mod saws and work saws are two differant things.

 

[rahtreelimbs]

Rich, The baddest mod saws and work saws are two differant things.

OK, The baddest modded woods saws.

 

[spacemule]

Frank, I am not going to dig through engineering texts to prove a point.


I guess what I am getting at is the husky rep would probly be saying two rings are better than gold if husky had all two ring motors.

As for the model engines. Arent the bores tapered with the ringless designs?

Rich, The baddest mod saws and work saws are two differant things.

As I understand it, they're tapered but expand to a more cylindrical shape when at operating temperature.

 

[Crofter]

Ben. Any one text that someone might dig up is not necessarily the proof of any pudding. Even if it happens to have the stamp of the ASME or SAE. Sometimes the parameters may have been too narrow and also it is easy for some unperceived condition slip in and skew the results, best intentioned as the testers may have been. If you consider that some tests set out to demonstrate a particular products superiority for advertising purposes forget its legitimacy. I dont like to be too quick to make up my mind and I also have lived long enough to know you better be willing to change it sometimes.
Yes the ringless model engines are machined with the top of the bore smaller at room temperature. At operating temperature that part of the bore and the piston will both expand enough to give a uniform diameter with the lower bore. They can get some amazing horsepower from fractional cubic inch engines that weigh ounces. Some things suffer problems of scale so I think you might not extrapolate that to thinking NO piston rings would be better than two or one in a chain saw!

 

[spacemule]

That was my thinking, Frank. I was just curious if anyone had tried it. The dirt the typical chainsaw ingests would likely destroy a ringless setup in a few tanks of fuel. Of course, this is pure speculation also. Model engines are run with no filter, so the setup may be higher quality than we give it credit for. I agree with you about being too quick and too firm in our perceptions. If any one design is greatly superior, as has been said, it would almost certainly and quickly obliterate the competing designs.

 

[bwalker]

If any one design is greatly superior, as has been said, it would almost certainly and quickly obliterate the competing designs

This has already happened and two rings have been voted the winner.
Think about it this way. If single ring designs where so great why are they not in wider use? With the inherrent cost savings of a single ring piston you would think it would be a no brainer.

Rich, Just because a saw is fast doesnt mean its of a superior design. harley had a fast rodracer at one time. The design still sucked.

 

[spacemule]

This has already happened and two rings have been voted the winner.
Think about it this way. If single ring designs where so great why are they not in wider use? With the inherrent cost savings of a single ring piston you would think it would be a no brainer.

Rich, Just because a saw is fast doesnt mean its of a superior design. harley had a fast rodracer at one time. The design still sucked.

Think of marketing, Ben. Every Jo Blow homeowner automatically thinks 2 is better than one. And single rings are in farily wide use.

 

[bwalker]

Spacemule, I am not just talking saws here. Dirtbikes, snowmobiles, outboards, etc, are 99% dual ring.
BTW your average homeowner type knows next to nil about rings or the number of which his woodshark has.

 

[spacemule]

Spacemule, I am not just talking saws here. Dirtbikes, snowmobiles, outboards, etc, are 99% dual ring.
BTW your average homeowner type knows next to nil about rings or the number of which his woodshark has.

Companies often use the customer's ignorance to market their product. What's your point?

 

[bwalker]

My point is ring design is of no concern to the average saw buyer.

 

[Crofter]

A one ring piston can obviously get good sealing. What then does the second ring do. It will not be exposed to the gas pressure to expand it against the wall as effectively and maintain its stability in the groove. At such time that the upper ring is starting to experience enough ring end gap growth it may be able to come into play. If the customer were convinced by advertising that two was better, the other manufacturers would likely have to throw the extra one in just to satisfy the perceived benefit ( psychological) of it.I dont see circumstance that could be influence by advertising hype to be mechanically conclusive.I still need the saw mechanics experience.

 

[bwalker]

What then does the second ring do.

It transfers heat out of the piston(1 of the rings main functions) and improves the bearing area.
Think about why Husky is sending two ring 372's to the US while the rest of the world gets single ringers. What operating conditions specific to the USA are causing them to do this?
Ill give you a hint....EPA....RFG.

 

[Crofter]

Ben, you say that the second ring improves the pistons bearing area. My understanding is that the piston rides in the bore on a capilliary oil film. the ring is free to move laterally in all directions in the ring groove and the ring is less in width than the groove is in depth, so the piston cannot push on it against the bore. Only through the locating pin in the ring gap, can the piston bear on the ring at all, EXCEPT straight up or down. Any gas pressure between ring and piston is free to equalise 360 Deg. so that cannot support the piston via the ring either.
I think you will agree that the main actuating force to ensure sealing between ring and bore, and between ring and piston, is gas pressure above and behind the ring, and that initial expanding tension of the ring is minimal in sealing effect. The pressure differential creates the applying force. Any leakage past the top ring that is trapped between it and a lower ring would serve to decrease the pressure differential at the top ring. At the upper rpm limits, the importance of maintaining the rings tightly against the bore and the lower side of the ring groove as opposed to rattling from top to bottom, makes the difference of whether you will have early ring failure. In this scenario, a single ring can have an advantage. Granted this is in the area of pushing maximum piston speed and G forces. If two rings clearly shared the load and spread the wear evenly between them and if the one had no diminishing effect upon the other, it would be quite likely there would be a clear advantage. I also can see that a pair of rings will likely seal better at cranking and idle speeds where ring tension is the primary sealing force rather than gas pressure. Ring gap is also greater cold. What intuitively seems like such a simple, no brainer, may have a little more to it than first meets the eye!

 

[bwalker]

Frank, When I am talking about bearing area I am reffering to the amount of ring in contact with the cylinder wall. Two rings typicaly have more contact area than one.
As for the issue of ring flutter at high rpm or rather high pistons speeds(not the same). I think think ring thickness and type as a much greater in fluence on this than number of rings.
Also consider the fact that many times single ring designs use thicker rings than dual ring designs. This would tend to make them have higher higher likelyhood of fluttering.
BTW Fluttering is typicaly caused by the acceleration deceleration of the ring in the grove as the pistons chnages direction and is not a function of lack of sealing pressure. Hence the reason heavier rings flutter more than lighter ones.
Besides has anyone calculated the piston speed of a saw. I would bet flutter isnt even a issue.

 

[Molecule]

two rings piston tops ... weaker ?

I'm not a techie, but ... seems to me that a 2-ring piston has an extra groove in the piston top ... potentially making the piston top structurally and mechanically weaker (and any distribution flaws during the molding process more critical), allowing more stretch of the piston top at high rpms. Certainly the piston material between the two rings is structurally "weaker" or has "less support" for the work it has to do than the rest of the piston. Also, each time that 2nd ring (heaverier-more dense than piston material) has to switch from accelerating upward ... slight pause ... downward, (2 x 13000 times per min) there is an additional "slam-reversal" working against the groove bouindaries, which might generate more heat than it might dissipate.

As a quick solution, I'd look at what the Germans and Russians do. They tend to believe that truth is better swayed by hard scientific investigation than by popular opinion (esp. of an over-confident populari which has been so thoroughly brainwashed by Vicious Madison Avenue Marxists that it has bankrupted its family farmers, and still thinks "The Economy is going Great!")..

Uh oh, Molecule's going political again. ...