Read valve build?

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MANesler

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I am new to the hot saw world but have many years of experience on 2 stroke atvs and bikes. I was wondering why I never see old saws with reed valves be built into race saws? I was always under the impression that reed valves were a huge provement for 2 strokes, and aloud for a longer intake duration. And more air fuel? Any thoughts and opinions would be appreciated. PS does anyone have a 120cc + saw with reed valve intake for sale?
 
I hear boost ports are are really easy to add to a reed valve engine, channel them right up through the intake port but I have never personally used them......


All the old guys built reed saws cause that's way they had, I can't say for sure but I think it has to do with what your needs are whether you use reed valve or no
 
You are misinformed about a couple of issues. Reed valves have been around for years and years. I have a small common brand built saw with some genuine reeds. This particular saw is at least 30 years old. Tuning an engine with reeds can be very effective, but there are many negatives also. The first question is what do you want? There is no problem building a lite weight saw motor that could have as much as 80 BHP, but why. If you want to follow this thread look up tuned exhaust which has come up several times in just the last 6 months. A two stroke motor can not produce a large amount of power without the aid of tuned exhaust. So if tuned exhaust is used then you will have an inconvenient monster. Manufactures have stayed away from tuning engines with reeds because they do not want to add to the complexity, diminish longevity, cost and sacrifice reliability for a couple extra horse power. The modern reeds are usually made out of composite materials that have a known life span. Often saw motors that have reeds were made with stainless steel pedals that have a fairly long life, but they were quite crude as compared to off road ATVs. Thanks
 
I was not looking to build a saw for longevity, just raw power. I was planning a a tuned pipe. And thought a reed valve saw would be a good platform to start with. Had anyone built an old reed valve saw, and have an opion on this?
 
Well man if raw power is what you are after then that will be interesting. I have never heard a saw manufacture that was interested in power. However there are so many ATV motors to chose from both used and new. How about a CR 500 either air cooled or liquid cooled. With a tiny amount of tweaking 80 BHP is easy. Or a 80cc RM both air cooled and liquid cooled at a solid 30 BHP. With 30 BHP available what type of chain would you use? It seems like with a large amount of raw power chains would let go left and right. I have watched competitors mostly use modified MX motors. From what I have seen most competitors are in the 20 BHP range. A Stihl 090 even modified will not come close to that. I have taken a piston port engine and welded a reed cage to it with great improvements, but it really did not produce any more power just more torque. Please let IS people how it is going. Thanks
 
Ted what saw did you add the reed cage to?. I noticed homelite and Mcoulch both had saws around 120cc's with reed valves, that is what I was thinking about using to build......if I can find one at a reasonable price. Also with more torque I should be able to run a lager drive sprocket? Right. I really appreciate the wisdom. Thanks for the help.
 
Can reed valve float like valve springs on a built go cart engine?

That is an interesting question. The answer is maybe. A reed induction not read to be accurate. The whole system is some what based upon changes in air pressure. Air goes into the carburetor mixes with the fuel vapor because there is a vacuum created in side the combustion chamber. When the piston after drawing air in starts to go up in the compression stroke some of the air is pushed out the carburetor thus loosing some of its pressure. Also with tuned exhaust the previous stroke has expanded at a critically timed moment and has created a pop which pushes the out going air back into the combustion chamber thus supercharging the engine. With reed induction the air can go in, but can not go out. Pretty much like a one way valve. The drawback is that the reed cage causes friction and a drop in the available air that is being drawn in. So to compensate for that fairly large reed cages are made so that a little as possible air pressure is changed. Yes reeds can flutter or max out with RPM. Often if the reeds are floating the engine does not suddenly stop or have a decrease in power. At high RPMs reeds loose a some of their efficiency. Most reeds that I used were two staged. Often I used a tapered carbon fiber type reed or a long fiberglass reed with a short reed covering some of the pedal. The longest reed would be activated with small amounts of air pressure drops thus giving the motor excellent low RPM torque, but the shorter reeds would be much stiffer thus limiting the reeds fluctuation at higher RPMs and then you have extended the HP into the high RPM range.

Chain saw motors are junk compared to modern ATV 2 stroke motors. The chain saw is built simple low performance with an eye towards being as reliably as possible for many years. BTW chain saw makers build their motors as cheap as possible. Inspect any cylinder wall plating and you will find that the plating is very thin. The cylinder that I used for modification was off of a MX motor and was air cooled for simplicity. Thanks
 

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Ted what saw did you add the reed cage to?. I noticed homelite and Mcoulch both had saws around 120cc's with reed valves, that is what I was thinking about using to build......if I can find one at a reasonable price. Also with more torque I should be able to run a lager drive sprocket? Right. I really appreciate the wisdom. Thanks for the help.

If you're serious about building an old modified saw, look at McCulloch kart engines. They can be easily modified for more speed/"power", and they can be made to retrofit into the older Mac saw frames.

Just because a saw has more torque does not mean that you can put a bigger sprocket on it. Yes, the saw will pull it better, but there are limitations. With a standard bar, the chain will be thrown alot, b/c when the sprocket is bigger than the bar, the sprocket will not allow the chain to fully "seat" in the bar. "Fat-belly" bars help aid this problem.

Also, a razor-sharp chain is more important than a bigger sprocket. In a race, a wicked sharp chain running a 7 pin sprocket will cut faster than a slightly dull chain running a 9 pin sprocket.

A combo of both can be exciting... [emoji3]
 
Reed cage will restrict a piston ported engine without a tuned exhaust. You would need to look at rotary valve. This it why chainsaw porting does not incorporate the enhancements you see on modern dirt bike engines. This experiment has been tried.
 
I took a 71 suzuki ts125 2t motorcycle. And cut 1/8” off the bottom of the piston skirt. It’s a piston ported engine. This old bike was beating newer kx80’s in the straights. That’s reeds vs piston ported. I wanted to port it more but my son said at the time porting does nothing. Since then I let the kid learn on his own what works, now we port the bike engines.

We have so many tricks we can do to a piston ported air cooled engine.

The water cooled bikes allowed more port timing which creates more heat but the LC takes the heat away. Now how far can we go with the air cooled engine in changing the port timing I’m not sure. We also need to advance the timing a tad too. All the changes work together. Doing only one change means nothing.
 
The truth is that 2 smoke motors on dirt bikes are long gone. The potential is there, but suspension is not. The kids bikes will be phased out completely soon. However 4 strokes with an abundance of titanium have progressed really well. It is extra special to pull one of my smokers up to the gates and watch the jaws fall. My 250's which are not 250's any more have enabled me to get the hole shot all most every time. BTW port timing is completely different than ignition timing. To raise the ports you will achieve much greater HP, but sacrifice in a much shorter power band. HP is nice, but rarely wins races. Controllable torque is the ticket. If ignition timing is increased near 1% the low end torque increases, but HP starts falling immediately. Back in the day the air cooled cylinders were often hacked up to weld reed cages on them for the hidden nuggets of torque. Thanks
 
Two stroke bikes are coming back little by little. The European manufactures realize there’s a nitch for two strokes. The vintage and post vintage bikes are sought after for netra racing. There was mossbarger reed setups for the older huskys and other bikes.

http://www.mossbargerracing.com/

Do you think there’s a water cooled chainsaw in our future of high tech saws.
 

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