reed valve saw modding

[volks-man]

after my first, successful, porting job on my piston ported echo cs-440, i am thinking of opening up the little cs-346.
problem is that it is a reed valve motor. what differences am i likely to encounter inside this little saw?

do all the usual porting rules (ala blsnelling + others) apply?

pointers, tips, warnings?
thanks!

 

[blsnelling]

On my SXL-925 I only mildly ported the exhaust port. It made a noticeable difference. I have no idea how to mod the intake side.

 

[heimannm]

I'm watching and waiting...

Mark

 

[volks-man]

On my SXL-925 I only mildly ported the exhaust port. It made a noticeable difference. I have no idea how to mod the intake side.

theres got to be some sort of intake port, right? the reed valve is out near the carb? if the port is much smaller than the passage from carb/reed then i would guess you could open that up.
are there transfers on a reed valver? or does the piston drop low enough at bdc to let the charge enter above the top?

 

[Javelin]

Not sure how the reed is in your saw! However on the old olympic rl350 saws we would open the exhaust and take the reed plate and bore out the plastic intake manifold larger allowing more flow! It really woke up those little saws!

 

[volks-man]

Not sure how the reed is in your saw! However on the old olympic rl350 saws we would open the exhaust and take the reed plate and bore out the plastic intake manifold larger allowing more flow! It really woke up those little saws!

just have to be carefull not to bend/warp/damage the reed when you work near it?
i understand that they must be perfectly flat to seal properly.

 

[Jacob J.]

If it's direct crankcase reed induction, about the only thing you can do is find a bigger reed cage and carb. I know on the P-series Pioneers, it was common to mount a larger intake block and reed cage from one of the big Homelite saws.

 

[blsnelling]

So am I to take it that there is no "intake port timing" like found on a piston ported saw?

 

[Saw Dr.]

You're a little behind on the sig, Mark...
A good place to start is the reed cage. The reed petals only need .020" or so around the edges to seal. Usually there is quite a bit of meat there to make up for manufacturing differences. Just don't take off too much.....
Port timing is port timing. Once the charge is past the bottom end, everything is the same as far as changing port height etc.

 

[Jacob J.]

Typically you'll find non direct reed induction saws to have much more intake timing than a piston ported saw. The Mac 125 is a real good example of that.

 

[atvdave]

This is very interesting to me. I used to race 2 stroke ATV's and the single best improvement the the engine was a reed spacer, and power reeds. It really keep-ed the motor in the power band longer and harder with much more power. Even a aftermarket muffler, and porting job didn't give me more power over the reed's and spacer plate.

I'm new to the power chain saws so I have no idea about mods.... YET... But it would be nice to have a spacer plate, and power reeds... I think it will help a lot in the power band. However I would think that you would have to put larger jets in the carb for more fuel.

 

[Jacob J.]

That idea does translate over to saws. They were aftermarket products available for the big McCulloch and Homelite engines which incorporated spacers and reed blocks with more reeds or bigger reeds. There was a two-stage reed available for the Pioneer P-series saws.

 

[Banshee]

I'm very new to this chainsaw thing so take my advice at that.
I found it strange the chainsaws don't even use reeds.
When it came to reeds in atv's/Banshees there wasn't a whole lot you could do. The ports on a reed motor is huge anyway compare to a non reed motor.
You just slap in a couple of spacers and some Vforce 2's or 3's and your done on that end. The other end was where you put your time/money with porting and pipes.

I don't know what options you have in chainsaws, but I would think a chainsaw would have one big reed.
One big reed will tend to open later than the optimum time and is not going to be as precise as mutiple smaller multi-stage reeds.

Not knowing exactly how the chainsaw reeds are made-I would think and easy option would be to take pedals from a thinner more responsive reed and make it fit.

The next option would be to find a reed valve with mutiple smaller multi-stage reeds and custom fit it to your saw.

Again I really don't know. I'm just trying to throw some ideas out.

 

[Banshee]

This is very interesting to me. I used to race 2 stroke ATV's and the single best improvement the the engine was a reed spacer, and power reeds. It really keep-ed the motor in the power band longer and harder with much more power. Even a aftermarket muffler, and porting job didn't give me more power over the reed's and spacer plate.

I'm new to the power chain saws so I have no idea about mods.... YET... But it would be nice to have a spacer plate, and power reeds... I think it will help a lot in the power band. However I would think that you would have to put larger jets in the carb for more fuel.

I've always thought different. I've always thought the pipes were balls of your motor. It was what controlled when and how long your powerband was.
In Banshees you could have Vforces with either Paul Turners or CPI's you had very different powerbands. (I know you still have to set up the rest of your motor-Bigger carbs for the CPI's etc..)

 

[Mike Van]

I'm very new to this chainsaw thing so take my advice at that.
I found it strange the chainsaws don't even use reeds.



I don't know what options you have in chainsaws, but I would think a chainsaw would have one big reed.
One big reed will tend to open later than the optimum time and is not going to be as precise as mutiple smaller multi-stage reeds.

Not knowing exactly how the chainsaw reeds are made-I would think and easy option would be to take pedals from a thinner more responsive reed and make it fit.

QUOTE]

A 4 c.i. Homelite has 4 reeds, each approx. 1/2" x 3/4" mounted on a 4 sided block. They're pretty thin stainless steel. Problem I see with adding spacers, etc, is the carb has to fit back in the box with the air filter. There's not a lot of room in there.

 

[volks-man]

If it's direct crankcase reed induction, about the only thing you can do is find a bigger reed cage and carb. I know on the P-series Pioneers, it was common to mount a larger intake block and reed cage from one of the big Homelite saws.

i think i understand the direct crank reed induction statement. i had a poulan micro here and if you looked under the reed block you could see the crankshaft.

heres a page from my ipl. this is a clamshell motor. it looks like there is an intake port on the back of the lower clamshell! now, how does the intake charge get in to the cylinder? transfers right? bewildering, these reed valvers.

 

[blsnelling]

It gets to the combustion chamber the same way as a piston ported engine. Like you said, via the transfers. The fuel charge comes into the engine as the bottom of the piston skirt clears the bottom of the intake port as it moves upward. As the piston comes down after ignition, the charge in the base is forced out of the base and moves up through the transfers. The exhaust is blown out and a fresh fuel charge introduced to the combustion chamber. Did I get that right?

 

[mountainlake]

It gets to the combustion chamber the same way as a piston ported engine. Like you said, via the transfers. The fuel charge comes into the engine as the bottom of the piston skirt clears the bottom of the intake port as it moves upward. As the piston comes down after ignition, the charge in the base is forced out of the base and moves up through the transfers. The exhaust is blown out and a fresh fuel charge introduced to the combustion chamber. Did I get that right?

Not quite, the fuel comes in through the reeds as soon as the piston starts going up, the intake port is the reed valve. Otherwise it's right. If you want to see some huge tranfers take apart a modern snowmobile engine. Steve

 

[blsnelling]

I was describing a piston ported design. So a reed engine has infinite intake duration?

 

[mountainlake]

I was describing a piston ported design. So a reed engine has infinite intake duration?

Soon as the piston moves up far enough to create a vacume to open the reeds (they open easy) it is on intake, soon as the piston starts coming down and create a little pressure the reeds close and the mix is forced through the tranfers. All the hi performance 2 stroke snowmobile engines use reed valves now making thier best power around 7400 to 8200 RPM on stock sleds. If saws made the same hp per cc as snowbobiles a 70cc saw would have 13.3 hp. Liquid cooling sure helps, not feasable in saws . Steve