Piston Rings: SGL vs DBL

[shooter]

Saw a post on another forum recently with the following bit of "wisdom":

"2 piston rings equals pro saw, 1 ring equals ranch saw."

Over the years, looking at various size saws in both the Husky & Jonsey lineups indicate that both single & double ring designs are utilized. Dolmar certainly uses single ring designs.

My book indicates that the Husky 55 Rancher is a single ring design, yet the chainsaw certainly has a reputation for being one of the more durable, dependable models on the market.

If the general perception is out there that single ring piston designs are lower quality, what is behind the reasoning?

 

[eyolf]

Tomatoes are also a member of the same family as black nightshade and Jimsonweed. People thought they were poisonous because you can't eat nightshade and tobacco, for example.


30 or 40 years ago, single ring setups were the hot ticket for performance in 2-strokes. Especially the "L"-section dykes rings. Of course they didn't last as long as two-ring pistons, for various reasons...sometimes just because the single-ring engines were run pretty hard on race bikes and snowmobiles. Some people will eventually compare them to the 2-ring setups in the lower-performance bikes and sleds. Or even the 3-ring pistons in some of those old outboards.

Lots of the snomobile, bike and outboard engines were expected to give good long service life, but there was a lot more to it than how many rings they had.

I have a Jons 670 with a single ring piston; stuck the piston last year because of (take your choice): (1) old gas, (2) hot day, dusty, rotten box-elder clogging up cooling fins (3) working the heck out of it with long bar. Up to that point the saw had 9 hard years on it, a couple of hundred cords of firewood and however much other work, yet still probably had 140# of compression. If I had been smarter with the saw, I'd still be on that original piston/ single ring without complaint.

Just my $0.02

 

[stihltech]

rins

I asked Ben Crago about the ring issue. He clearly stated that it was a piston stability issue. Whether or not it will make a well maintained saw last longer, I don't know. I do believe it helps on a large dispalcement saw, but we all know there are many single ring saws still running, 041 Farmboss and 009 come to mind.

 

[bwalker]

Double ring pistons are better than singles in almost every case. Just ask your local Ski-Doo dealer about series-3 piston rings.

 

[eric_271]

less drag with one ring less friction. Fact

 

[bwalker]

Less bearing and heat sink area. Fact.

 

[hotrodusa]

All the smaller husky saws that I had apart, have single ring pistons, 372xp and up use two piston rings

Reason for a single ring is less friction, which equals more power, adding another ring would not add much compression, maybe 10%, you'll actualy loose horse power by the added friction of the second piston ring.

on race & performance applications, it's common to use thinner and less rings, for less friction, which helps gain greater RPM's equals more power..........

There is more to it then what I explained, someone that builds & tunes race engines could do a better job of explaining then what I did.

 

[eric_271]

hotrodusa thats a bullseye. couldent have said it beyyer my self.

 

[bwalker]

FWIW# I have ran the same dirtbike with a one ring piston and one with a dual ring. I could tell no differance.

 

[eric_271]

it does show on a dyno Ben.

 

[bwalker]

I dont know as I have never seen dyno results that suggest so. I put very little faith in dyno results anyways as they are mostly a marketing tool.

 

[shooter]

Eric & Hotrod - How about the bearing surface & heat sink as Ben indicated?

Both parameters are desireable, for ring wear and heat transfer which = cooler operating temps.

 

[eric_271]

No ben they are a tool to measure hp. Do you think the factory just dreams up hp numbers for each saw.

 

[bwalker]

FWIW my 7900 is a single ring saw an it appears to work fine.

Check this thread out. http://snowest.com/fusetalk/messageview.cfm?catid=3&threadid=119367&STARTPAGE=1

Read the post by RKT.

 

[eric_271]

Ben from reading that it looks like doo would be well advised to call husky or dolmar and ask them what their secret is for makeing one ring saws last so long.

 

[bwalker]

I dont know why they dont, Mahle makes pistons for all three.

 

[hlw49]

The Husky 385 and down use mostly one ring pistons.

 

[hotrodusa]

Well the factory uses a dyno to determine were peak hoursepower is at what RPM, and this is how the manufacturer comes up with there specifications on what to set the RPM's at for a particular saw, just doesn't make sense to lean it out more to get more RPM's if the power aint there, it'll just blow up from running to lean.

When you do porting on a cylinder it changes the power band of the engine, the peak power is at a higher RPM, and to reach these RPM's you want as little friction (resistance) as possiable.

At the shop we have a husky 288 saw that pulls 19,000 RPM, thats were the peak power is, we have fun showing off with that saw...........


HLW49, no flames intended, but every 385xp saw I took apart had two rings in them. maybe there are some with one ring but I haven't seen it.


A piston ring for a husky chainsaw costs about 15.00, and changing them on a saw is a simple task.

motocross dirtbike racers put new piston rings in before every race event.
most 9.00 second and quicker drag cars change there piston rings at least twice a season........

To the avarage guy, changing a piston ring may seem like a big task that should not have to be done, No different then putting new tires on your car every so often.................

Well I'm all tired out..............................