reed valve saw modding

[volks-man]

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

so, in these engines, the transfers are fed by piston windows only? if there were transfers at the bottom of the cylinder, like my piston ported cs440, there would be difficulty in producing that vacuum and pressure as you describe it, no?

 

[brages]

At the top portion of its travel, the piston is sealing off the transfers, and the crankcase can develop vacuum and suck in fuel.

Really the only difference between piston-ported and reed-valved is the way the airflow into the crankcase is controlled.

I had a rotary-valved dirt bike (KE100)... another design, not frequently used in saws...

 

[056kid]

you might could make a little block to go inside the reeds that helps flow the air when it is moving fast. Mabe go behind them and see if you can free up some space for more charge.

I wish i had my honda jug off to stare at..

 

[atvdave]

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 found it to be very different on my blaster, and TRX250R. I had all the aftermarket stuff... LRD, DG, FMF & CT pipes, LRD, & CT porting, larger carbs, K&N filter mod... ect...

But the best power band improvement was with the RAD valve, spacer plate, & the Boyesen reed valves. When you hit the power band it would fell like your ripping your arms out of there socket.

I think the Banshees had many good things going for them, but the twin Jug, & carb combo was hard to dial in sometimes. However I've been to a few sand dunes in my life time where the Banshee would just flat out whoop A$$. Unless of course there was a LT500 around.

 

[volks-man]

anyone been inside one of these echos?
anyone know what that hump is on the back of the clamshell?
anyone have a factory service manual for echo cs-346?
i really want some kind of understanding of how this thing ticks before i open it up.

 

[heimannm]

My 3-25 (1948) had a rotary valve, lots of old Homelites had rotary valves as well.

Rotary valve connected to the crankshaft

Cover installed, rotary valve closed

Cover installed, rotary valve opening

Hard to see in my poor photo but you can see the transfer port on this McCulloch cylinder from my 650.

All of the old reed valve McCullochs were advertised and "reed valve with third port injection"

Volks, I think the "hump" as you call it is the close fitting cover on the end of the crank case. The tighter the space, the greater the pressure differential (vacuum/pressure) as the piston moves up and down.

Mark

 

[GPH85]

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.

Any chance these aftermarket parts for the Homelites are still available? Any chance you may have some of these to show or even possibly sale?

Here's what I believe everyone has been talking about with some of the reed modding... This is what I more commonly see done to reed assemblies I buy that were supposidly stock. Evidently someone modded them - did or didn't see gains - not sure why they stuck them back in the box in a new but modded state?

You should be able to see the little pyramid that was added in the center and where someone did some port work to the cage seats. I'm saving this one to go in my modded saw when I get it back together...

 

[volks-man]

My 3-25 (1948) had a rotary valve, lots of old Homelites had rotary valves as well.

All of the old reed valve McCullochs were advertised and "reed valve with third port injection"

Volks, I think the "hump" as you call it is the close fitting cover on the end of the crank case. The tighter the space, the greater the pressure differential (vacuum/pressure) as the piston moves up and down.

Mark

interesting. i have heard of rotary valves but never have seen one before.
thanks for the pics!

the hump i am referring to is on the crankcase end cover (see ipl in post above). in the ipl it looks a lot like a conventional intake port, but on the bottom end of the crankcase. what i haven't figured out is how the intake charge gets in to the crankcase, and a port located there would answer my question.

i'm going to have to take a peek inside this little saw to understand it.

 

[Tzed250]

Two types of reed valve induction. Case-reed and piston port. The piston port type works just like a non-reed piston port engine, except for the fact that the reed blocks reverse flow through the intake, allowing longer intake durations. The case reed engine relies only on pressure differential to open and close the reeds. Case reed engines are very friendly to their pistons, as there is no window in the cylinder, allowing the skirt full contact.

 

[volks-man]

Two types of reed valve induction. Case-reed and piston port. The piston port type works just like a non-reed piston port engine, except for the fact that the reed blocks reverse flow through the intake, allowing longer intake durations. The case reed engine relies only on pressure differential to open and close the reeds. Case reed engines are very friendly to their pistons, as there is no window in the cylinder, allowing the skirt full contact.

i suspect that this is a piston ported reed valve engine.

interestingly enough, my piston ported echo-cs440 has no reeds, and no piston windows. i still haven't quite figured that idea out either.

 

[mustard]

I presently have an echo cs-3450 ( almost the same as the 346) apart.

The reed valveand spacer block is located under the carb, the fuel mixture goes into the bottom of the crank case.
The piston is a full skirt one with no ports in it.

The transfer/intake ports are on each side of the cylinder and there are 2 per side, one smaller /narrower than the other.

They are a continual slot,each seperate, that go right from the crankcase to well up into the cylinder, like a trough, open to the cylinder all the way down.

I will be following this post to see what we come up with on modding these engines as I would love to do a little work on mine.
Perhaps someone knows of a supplier that sells reed valves?
Greg

 

[mustard]

I just took some measurments.

My reed block has a straight bored hole at .630 dia.

- the reed dia is .746
- the carb outlet is .563 and
- the carb inlet is .375

 

[mustard]

I also checked the squish on my 2 echo -3450's, one real old one and both had the same squish, right at .045. Pretty bad but hard to do much with it though I have a machinist friend and he has a couple of ideas. Not easy on the clamshell mtr. though.

Anybody know of any outfit that does alot of piston welding/machining?

 

[mustard]

I am also looking for NEW echo cs- 3450 /346 parts as below

- piston ring set

- piston

If you have some or know of a cheap place to get them , please advise.
Thanks
Greg

 

[sonic_v]

reed petal setup

You could measure up your reed petals and use the following programme to check the natural frequency. If this frequency differs much from your peak power speed you could either obtain different thickness petals or adjust the petal free length.

http://www.torqsoft.net/reed-petal-design.html

 

[mustard]

Thanks so much for the info.

I think the small thin reed in this echo does not work in their programm but it is a great site.

greg

 

[edisto]

For what it's worth (which isn't much because I've never had a saw with reeds):

one problem I have read about with reeds is the tradeoff between having them thin enough to open easily (effectively increasing duration), but stiff enough to not flutter at high RPMs. I don't know what the likelihood is of getting aftermarket reed material small enough would be.

Other typical modifications seem to be opening up the inlets toward the attachment point of the reeds, and the use of "stuffers"...the inlet on the crankcase side can often be too big for good flow, which affects how early the reeds open, so on bikes I have read about using plastic inserts to restrict the opening.

On bikes, one of the advantages of moving the inlet to the crankcase was that it left a lot of metal and space inthe cylinder for boost ports...but that's going overboard (especially on a clamshell!).

Mark...thanks for the pics. I didn't know there were saws with rotary induction! That could be a lot of fun...

 

[sonic_v]

Reeds

What is the thickness of your reed petal? Also, how many are there and what is the material?