One ring vs Two rings on 2 stroke chainsaws

[FATGUY]

This cr@p is hilarious...

how so?

 

[Lakeside53]

I think I'm begining to see the light.... so it's the combustion "charge" that wears the ring(s) and not the contact with the cylinder wall. Ok I'll buy that.

No.... The cylinder causes the wear. The combustion just pushes the ring onto the cylinder.

 

[Tzed250]

how so?

All the guessing, opinion, hearsay, conjecture, assumption, falsehood, etc.




.

 

[cord arrow]

how so?

LOL...so YOU'RE the one garnering useful information from these redundant meanderings...

I just knew this thread was not a complete waste.....

 

[Jacob J.]

All the guessing, opinion, hearsay, conjecture, assumption, falsehood, etc.




.

I just leave it at the assumption that the engineers know what they're doing. I figure a guy who has a doctoral degree in mechanical engineering is a few notches above me when it comes to designing things and knowing what to put where.

 

[FATGUY]

Don't kid yourself, the BEST engineers come from the floor. There are things you may not know, but they're a lot easier to learn than feel and common sense. If an engineer won't listen to the opinion of a tradesman, he'll quickly be embarrassed.

 

[cord arrow]

a guy who has a doctoral degree in mechanical engineering

Doctoral? Oh yeah...these guys are doin' chainsaws...

 

[Jacob J.]

Doctoral? Oh yeah...these guys are doin' chainsaws...

You'd be surprised to see how many master's and doctoral degrees are on the payroll at Stihl and Husqvarna AB.

 

[Jacob J.]

Don't kid yourself, the BEST engineers come from the floor. There are things you may not know, but they're a lot easier to learn than feel and common sense. If an engineer won't listen to the opinion of a tradesman, he'll quickly be embarrassed.

I agree with that to a point, but you still need engineers to do most of the design work. The input of servicing technicians is important and that's why McCulloch and Homelite had their engineers and sales staff go out and live in the logging camps for a week or two at a time. I met two engineers from Husqvarna here a few years ago, they came out to several job sites and worked with some fallers on the design upgrades for the 372 and the 395.

 

[FATGUY]

You'd be surprised to see how many master's and doctoral degrees are on the payroll at Stihl and Husqvarna AB.

I'm not taking anything away from them, they've earned the right ot be there.

 

[cord arrow]

Perhaps...but I've a couple in my employ...and they wouldn't know a chainsaw from a miter saw...but you can bet given five minutes here we would all be in our place.

Now..if you need robots that make the world go round...these are your guys...

 

[J.W Younger]

guys, I,m so ignorant of 2-strokes I don;t even know what questions to ask,so trust me I am not trolling. When you start talking port timing ,lost here but wanna learn more.one thing for sure is I,m not gonna grind anything if I don,t know what for. needa ground level basic stuff education before askin anything complicated so maybe I,ll just shut up and read.

 

[Team FAST]

some karting background

Hi,

I've followed this thread with some interest. I have a background racing karts, specifically 100cc air cooled sprint karts, and roadracing 125cc shifter karts and most recently 250cc Superkarts.

With the 125cc shifter karts, we are using MX derived engines, typically CR-125 and YZ-125 liquid cooled two strokes. The engines are square....54mm bore x 54mm stroke and use nikasil plated cylinders. The hot 125cc setup was a Honda RS-125 cast racing piston using a single Keystone style ring. This is a GP motorcycle racing piston. We spent many hours on the dyno working on the engines, optimizing them for pipes, digital programmable ignitions (with multiple advance curves) and of course the intakes....all used reed valves.

There were some earlier comments from racing MX guys about high rpm stress on engines, etc. Believe me, compared to a high speed roadracing application (kart or GP bike) the MX bike is more like a tractor.....braap brapp braap on and off the throttle constantly to get around the course. If you look at my data acquistion traces, over a typical lap, the karts spend a LOT of time at WOT and high rpm around a racetrack like Road Atlanta, or Mid-Ohio. I would typically see a drop in power output after a 20 or 30 minute race. Keep in mind that these are 125cc engines water cooled using expansion pipes revving to peak power at 12,500 to 13,000 rpm. Typical competitive horsepower for 125cc shifter motors are in the low 40s, 250cc singles are 65 and 250cc GP twins are 90-100 hp. So I would replace the ring on my 125cc kart motor after about 30 minutes.


Single rings are best for high revving motors to reduce friction. Dual rings improve longevity and heat transfer, and would make sense for a consumer product like a chainsaw where engine life is more important than all out performance. If I was building a high performance chainsaw for competition usage, I would opt for a single ring piston, knowing that I would be changing it more frequently. This assumes Nikasil plated cylinders.

thanks,
-erik

 

[cord arrow]

That is a great first post...kudos.

 

[FATGUY]

Hi,

I've followed this thread with some interest. I have a background racing karts, specifically 100cc air cooled sprint karts, and roadracing 125cc shifter karts and most recently 250cc Superkarts.

With the 125cc shifter karts, we are using MX derived engines, typically CR-125 and YZ-125 liquid cooled two strokes. The engines are square....54mm bore x 54mm stroke and use nikasil plated cylinders. The hot 125cc setup was a Honda RS-125 cast racing piston using a single Keystone style ring. This is a GP motorcycle racing piston. We spent many hours on the dyno working on the engines, optimizing them for pipes, digital programmable ignitions (with multiple advance curves) and of course the intakes....all used reed valves.

There were some earlier comments from racing MX guys about high rpm stress on engines, etc. Believe me, compared to a high speed roadracing application (kart or GP bike) the MX bike is more like a tractor.....braap brapp braap on and off the throttle constantly to get around the course. If you look at my data acquistion traces, over a typical lap, the karts spend a LOT of time at WOT and high rpm around a racetrack like Road Atlanta, or Mid-Ohio. I would typically see a drop in power output after a 20 or 30 minute race. Keep in mind that these are 125cc engines water cooled using expansion pipes revving to peak power at 12,500 to 13,000 rpm. Typical competitive horsepower for 125cc shifter motors are in the low 40s, 250cc singles are 65 and 250cc GP twins are 90-100 hp. So I would replace the ring on my 125cc kart motor after about 30 minutes.


Single rings are best for high revving motors to reduce friction. Dual rings improve longevity and heat transfer, and would make sense for a consumer product like a chainsaw where engine life is more important than all out performance. If I was building a high performance chainsaw for competition usage, I would opt for a single ring piston, knowing that I would be changing it more frequently. This assumes Nikasil plated cylinders.

thanks,
-erik

+1 rep sent

 

[blsnelling]

Great post and info. Thanks.

 

[RiverRat2]

I would have to agree here.....................................

LOLOL!!!! Never a doubt!!!!!


BTW Good Post Team Fast and correcta-mundo!!!!!!!!

 

[PES+]

Were you running plain half keystones or dykes L

 

[edisto]

Piston stability and wear is a real issue in a close coupled piston ported engine. What applies performance wise in a four stroke might have little to do with some claimed advantages when applied to a 2 stroke. Dwell times around exhaust and intake events is about 90 degrees different in the two designs.

A longer rod for the same stroke would keep the piston at the top and the bottom of the cylinder for a longer period of time than a shorter rod. I can see the advantage (power not durability) to this for the top of the stroke, but I'm curious...would longer dwell time at the bottom of the stroke have a similar effect to opening up the ports by allowing a longer time for flow to occur?

 

[THALL10326]

Hi,



Single rings are best for high revving motors to reduce friction. Dual rings improve longevity and heat transfer, and would make sense for a consumer product like a chainsaw where engine life is more important than all out performance. If I was building a high performance chainsaw for competition usage, I would opt for a single ring piston, knowing that I would be changing it more frequently. This assumes Nikasil plated cylinders.

thanks,
-erik

Many years ago Stihl made a 024 with a single ring piston. Later that same model was changed to a two ring piston. I inqiured about that change and was told exactly what the above paragragh says. They made the change to increase the life of the engine and gave up some of the performance to do so. TEAM FAST knows what he is talking about,