fwgsaw
don't call me i will call you!!
From the 1950s I don't believe anyone has made a rotary valve chainsaw in a long time.
Reed Valves, why did they stop using them?
- Thread starter woodlandcammies
- Start date
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Not needed, as chainsaws only have to run at one speed, basically WOT.
Reeds have advantages of being able to locate the carb anywhere on the crankcase, not have to be located at piston skirt. They have wide range of operating speeds as not dependant on piston skirt and port timing. They are especially good at very low rpm range.
Downside (other bulk, weight, cost) is that they restrict air flow at high rpm. No matter how soft they are, there is a pressure differntial needed to hold them openand that cuts the flow.
For a saw, high rpm max power counts, so all of the downside penalities, and no real upside.
There are pure reed valve inlets, and there are piston ported with reeds in series, where inlet goes through the reeds, then past the piston ported inlet, then into crankcase. Many motorcycle engines that way. The reeds are soft, the port timing is designed for higher rpm, and the reeds help a lot at low end. They are soft and tend to float and stay open at high rpm, but there is still some penalty athigh speeds.
Reeds have advantages of being able to locate the carb anywhere on the crankcase, not have to be located at piston skirt. They have wide range of operating speeds as not dependant on piston skirt and port timing. They are especially good at very low rpm range.
Downside (other bulk, weight, cost) is that they restrict air flow at high rpm. No matter how soft they are, there is a pressure differntial needed to hold them openand that cuts the flow.
For a saw, high rpm max power counts, so all of the downside penalities, and no real upside.
There are pure reed valve inlets, and there are piston ported with reeds in series, where inlet goes through the reeds, then past the piston ported inlet, then into crankcase. Many motorcycle engines that way. The reeds are soft, the port timing is designed for higher rpm, and the reeds help a lot at low end. They are soft and tend to float and stay open at high rpm, but there is still some penalty athigh speeds.
cedarhollow
ArboristSite Guru
In respect to valves in chainsaws I wonder if Stihl will start making chainsaw with 4mix style engine. The km130 I got has not needed anything but oil and gas mix since I got it although I'm sure it is due for a valve adjustment and I keep thinking that the primer bulb is going to go but it hasn't yet. I should have put an hour meter on it when I got it.
that thing has tons of torque at any speed.
that thing has tons of torque at any speed.
TBS
I have chainsaws and chainsaw accessories.
Was at harbor freight and noticed their little 2 stroke generator has reed valves.
woodlandcammies
ArboristSite Operative
Ive got one of their two stroke generators that looks like a honda suitcase generator.. Man that thing is quiet, we run the snot out of it during race season... Good little guy for 250$.
woodlandcammies
ArboristSite Operative
Edit that- forgot the one we got was a 4 stroke with a tiny predator engine... My mistake... Still quiet as heck.. You can sit next to it and have a conversation without raising your voice at all. First tool I ever got that had a catalytic converter muffler as well.
RandyMac
Stiff Member
It sounds to me that a PP engine that has peak rpm of 12k+ and loses 3-4k in the cut is lacking in real power. I'd want a refund.
A McC Super 250 has max revs and power peak that are nearly the same, about 9,500 rpm and no need to baby it, to keep it from falling on it's face.
Many of the last generation reed valve saws ran similar.
A McC Super 250 has max revs and power peak that are nearly the same, about 9,500 rpm and no need to baby it, to keep it from falling on it's face.
Many of the last generation reed valve saws ran similar.
Yeah, the Pioneer P series are super impressive that way. I wish they still made them.
Big_Wood
westcoast dweller
does it leak fuel? lol i can't tell you how many of those generators have crossed my bench with a fuel bowl gasket installed incorrectly. amazingly those little beaters will do some hours and i've seen guys buy them for a specific purpose and just run them with 0 maintenance still invest my money elsewhere though lol i usually got a honda kick'n around but i've been putting some abuse on an old honeywell invertor generator i got free. shop said it would never run again but with a service and tuning it did. i got a fuel filter, spark plug, oil and a bit of my time into it and have been running it for 4 years now. just as quiet as a honda and rated at a genuine 2000watts rather then a peak of 2000 like the honda. they run lean and are crazy hard to start when new but with a little jet reaming they start pretty decent. not as good as a honda yet but acceptable.
