Single ring V.S. double ring pistons

[Lakeside53]

That was all informative but i got a new question to add to the mix.

Q.) Are double ring pistons more prone to scoring and siezing because of more friction?
I just had a double ringer sieze up on me even though I used premium gas & oil(non-ethanol 93 & Mobil 1 mxt2 @ 40:1) This was a fairly new saw(less than 4 gal of uel thru it) I have been on this site for a couple years now so I Know what a lean seizer is and i know the saw wasn't running to lean.

Sorry, missed the QUESTION!!

Answer- nope... "cos if they did there would be 15+ years of Stihl (an other) saws in landfills! But you must have another problem... What saw?? Any chance of an air leak?

 

[klickitatsacket]

Hey guys, I found some information on the ring debate. Apparently as much as 3% of the fuel charge can leak into the crevice between the double rings during the compression stroke accounting for as much as 80% of the hydrocarbon pollution. A 2 ring system will hold the charge in the cylinder better but what is in the crevice will escape out the exhaust port while on a single ring system most of what would be trapped in the crevice will simply be pushed into the crank case but at a greater loss in the cylinder as one ring allows more blow by. Power vrs. Pollution could be part of the reason for ring #'s. Double ring systems also have a better distribution of lubrication over a longer period of time. The pressurized system evenly distributes even if there is uneven wear of the piston skirt. On a single ring system; as the skirt wears on one side the piston tips allowing more fuel to one side and less to the other as the pressure will blow by the path of least resistance. Just some things I found interesting while researching this.

 

[bwalker]

Dean, the 80% figure may be applicable to four strokes, but not two strokes. The amount of unburnt HC lost during scavenging pales in comparison to the paltry amount trapped between the two rings.
Interesting non the less.

 

[klickitatsacket]

ben, you are right about the article pertaining to 4 stroke engines. With as much as 30% of the fresh fuel charge flowing through the exhaust on a 2 stroke the crevice is the least of the worries. the whole idea of lubrication and blow by was very interesting to me as well.

 

[FourMoCajuns]

There are some model aircraft engines with NO rings and they turn ungodly rpms. But you normally crash them before you wear out an engine.

 

[Marvinlee]

The chainsaw maker faces many trade offs in piston design. For the cost of a two-ring piston, he can choose instead a single ring design with a better piston ring material--possibly ductile iron--or perhaps go to a gas nitrided steel piston ring that will have exceptional durability. For the piston, the money saved in milling two piston ring grooves can be spent on a better alloy, more careful heat treatment, etc. Among other gains to a single-ring design, the piston may be a few grams lighter and that can mean lower bearing loads, faster engine acceleration, and possibly a millimeter or more shorter piston. Or, maybe the manufacturer simply saves a buck and accepts shorter piston ring life. Given the many variables involved in piston and piston ring design, my personal bias is to choose a reputable chainsaw maker and trust to his judgment.