Adirondack
ArboristSite Operative
Is there any difference between one or two piston rings? Does this mean better compression or longer life? What saws have two rings?
1 or 2 piston rings?
- Thread starter Adirondack
- Start date
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JONSEREDFAN6069
Wheeler McDealer
i know my jonsered 630 and 670 super has 2, not sure on others i own though never checked.
Octane
ArboristSite Operative
2-ring pistons are seen typically on what are considered to be more, "pro" saws because they offer more durability.
In the case of Stihls, their, "occasional use" saws/leafblowers/etc have 1 piston ring.
In the case of Stihls, their, "occasional use" saws/leafblowers/etc have 1 piston ring.
scotclayshooter
Addicted to ArboristSite
I have a 242XP a 262XP and a 7900 they all have only 1 ring these are all pro saws!
Trigger-Time
Addicted to ArboristSite
Lakeside53
Stihl Wrenching
Stihl saws since about 1983 (or so). I think the early 024 was the last one.
Search.... search search.... Lots of posts, many good, some crap, on this topic over the years.
BTW.. For those that don't think 2 rings last longer than 1... measure the end gaps on the upper and then the lower of a 2 ring piston. The upper always wears faster as it takes the brunt of the combustion. On a high time 70cc saw, it's not uncommon to see 25 thou on the upper, and 10 on the lower. I forget the exact gap on moderate time 3120 I re-ringed a few months ago, but it was about 50 thou, and the compression was way down.
Search.... search search.... Lots of posts, many good, some crap, on this topic over the years.
BTW.. For those that don't think 2 rings last longer than 1... measure the end gaps on the upper and then the lower of a 2 ring piston. The upper always wears faster as it takes the brunt of the combustion. On a high time 70cc saw, it's not uncommon to see 25 thou on the upper, and 10 on the lower. I forget the exact gap on moderate time 3120 I re-ringed a few months ago, but it was about 50 thou, and the compression was way down.
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The 254xp is also a 1 ring, mine is 11 years old and has cut alot and it still has150psi compression. I have always run 50:1 mix in it.
Hi!!
In competition 1 ring (higher RPM, lower weight, less friction...), but sure less duration, but in competition duration isn´t very important.
Curiosly 1 ring is cheaper(less material).
I think constructors trying to find the best of two worlds, 1 ring but nickasil or chrome cilinder for improve duration!!.
Earlier models with iron cilinders use two rings better than one.
In competition 1 ring (higher RPM, lower weight, less friction...), but sure less duration, but in competition duration isn´t very important.
Curiosly 1 ring is cheaper(less material).
I think constructors trying to find the best of two worlds, 1 ring but nickasil or chrome cilinder for improve duration!!.
Earlier models with iron cilinders use two rings better than one.
SawTroll
Information Collector
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My timber cutting saws run better with two rings...and they're going to stay that way.
Saw Dr.
Junk Collector
So what does that make the old Poulans and Remingtons with THREE rings?
kurtty
ArboristSite Operative
my 371xp only has one ring.
the acceloration on that saw is increadable. it just jumps to peak RPM instantly. i really notice it after i have been using my 372xpw for a while then switch to the 371xp
the acceloration on that saw is increadable. it just jumps to peak RPM instantly. i really notice it after i have been using my 372xpw for a while then switch to the 371xp
SawTroll
Information Collector
My MS361 has two rings, and accellerate real fast - I don't think there are any easy answers or "rules of thumb" here - several factors involved.......
harrygrey382
Addicted to ArboristSite
what are the disadvantages of two rings, apart from cost?
Magellan
ArboristSite Member
It's not much good to give a rule of thumb, since there are so many variables (like Troll said), but:
One ring: Less friction and weight
Two rings: More friction, durability and sealing
Edit: That's all things being equal.
For an example of some variables involved, consider a cast iron cylinder versus a plated aluminum cylinder, both with aluminum pistons:
Because of the durability of a modern cylinder plating process (Nikasil, ceramics), and the similarity of expansion rates between aluminum pistons and cylinders, tolerances between the piston and the cylinder wall can be tighter and you can run a single ring without losing efficiency. In an engine with a cast iron cylinder and an aluminum piston, the differences in expansion rates will force the use of a smaller piston and make a tougher job for the rings, so you want two or more to ensure efficiency and protection.
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Funny how I cut more timber in a day with my two-ring 372 than guys cutting right next to me with their single-ring 371s...
stihl86
Addicted to ArboristSite
The only 2 Stihl products I ever seen with 1 ring was a 015 and a FS36 (line trimmer)
I think the idea is one ring offers less friction which reduces heat. Two rings seal better. Old 3 ring seal best but alot of power lost to friction. Which is better, ?
scotclayshooter
Addicted to ArboristSite
Thats just Talent! Nothing to do with the rings lol
Wit the cost of rings im glad my262XP only has 1 £11!!!!
Flattery will get you everywhere...you just earned yourself a free piston ring for a 262xp my friend...
scotclayshooter
Addicted to ArboristSite
Flattery will get you everywhere...you just earned yourself a free piston ring for a 262xp my friend...
LOL
Im hoping my 262 will be kicking 372 butt soon, It be modding time!
Should be finished next week.
