FATGUY
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This cr@p is hilarious...
how so?
This cr@p is hilarious...
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.
how so?
how so?
All the guessing, opinion, hearsay, conjecture, assumption, falsehood, etc.
.
a guy who has a doctoral degree in mechanical engineering
Doctoral? Oh yeah...these guys are doin' chainsaws...
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.
You'd be surprised to see how many master's and doctoral degrees are on the payroll at Stihl and Husqvarna AB.
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
I would have to agree here.....................................
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.
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
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