Reed Valve

oscar89 · Post by **oscar89** » Mon Feb 16, 2009 5:49 pm

Do the JD sleds use a reed valve? What advantage are reed valves?

Cabindweller · Post by **Cabindweller** » Mon Feb 16, 2009 6:48 pm

Im no expert on these motors But seeings no one has replied yet. Deere used alot of Reed valved motors. But the early CCWs were piston ported. I belive that Reed valves become more common because they required less machining to build. Cheeper and easier to make a Reed valve cylinder than a Piston Ported Cylinder? I don't know enough to know if there are also performance gains with reed valve motors.

Jerry

JoeRainville · Post by **JoeRainville** » Mon Feb 16, 2009 7:05 pm

Deere's started using case reed valve motors with the 73 JDX-8 and its KEC 440/21 CCW motor. The last case reed motor was used in the 78 Cyclone and Liquifires in both 340 and 440cc's.

Jerry, a case reed motor is more expensive to build than a piston ported engine. They offer certain performace advantages, but it takes a lot of engineering to harness them properly.

For example, case reed motors allow for more transfer port area, and better fuel control since the 'back pulse" of the air/fuel mixture is controlled. The case reeds act like a check valve for air/fuel flow, only allowing it to enter the motor. Downside is that the material the reeds are made of can limit how fast the reeds can open and close, limiting top RPM. Kind of like valve float on a 4 stroke.

Modern materials now allow case reed motor to redline over 9,500 rpm, but not in the 70's. My 440 SnoCross sleds are about 110 hp, with reeds and power valve on the exhaust side, but the 440 Liquifire was only 57 hp at it's best in 78. Deere's high performance race sleds were not case reed, the 295/s, 340/s and Liquidator were aggressive piston ported motors.

However, all the Kawi motors Deere used from 79-84 were piston ported. They were lighter and cheaper than the CCW/Kiortz motors Deere used up til then.

I hope this helps answer a few of your questions,
-Joe Rainville

Cabindweller · Post by **Cabindweller** » Mon Feb 16, 2009 7:26 pm

There You Go. See I just learned something too. This place is a wealth of Knowlage.

Thanks Joe.

Joliet Jake · Post by **Joliet Jake** » Mon Feb 16, 2009 7:26 pm

The piston ported engines are simple in design. But because part of the charge is lost as the piston descends at low speeds these engines tend to get the blubbers at low speed.
But work very well as piston speed increases.

Many ingenious designs have been tried to overcome this trait, but none any simpler then to just install one way valves called reed valves, because of the similarity to reeds on a clarinet or saxophone.

With reed valve engines you get a broader power band and a tamer more trail friendly machine.

But as with anything there are trade offs and reed valves engines suffer at high speeds because of the blockage of ports by the reeds and the use of energy to open the reeds themselves.

Essentially reed valve engines have good low end characteristics and better gas mileage and no blowback into the air box.

Piston ported engines have better high end characteristics but at a price of a peaky power curve, blubbers at low RPM and a lot of blow back. into the air box

Case reeds engines are a combination of the two ????..but that?s a whole another story!

Once again this is a over simplified version.

Joliet Jake · Post by **Joliet Jake** » Mon Feb 16, 2009 7:29 pm

Didn't see your post Joe

nice job.......................

JDT · Post by **JDT** » Tue Feb 17, 2009 8:39 am

Joe do you have any thoughts on twin carb piston port engines that used a equilizer manifold, ie 634 Hirth?

Joliet Jake · Post by **Joliet Jake** » Tue Feb 17, 2009 8:19 pm

Please Forgive me for Hijacking your thread but??????

Like I said earlier piston port engines have low end blubbers because the fuel and air charge partially escape back into the inlet track at low speed.
Since carburetors don?t care which way the air passes though to work that charge picks up another fuel charge and as the port closes is abruptly stopped and pulled back in with the next cycle and along the way it picks up another fuel charge.
This results in a very rich mixture and subsequent poor performance.

Now for a worse scenario????in an effort to cure the poor low end performance the tuner leans the mixture by lowering midrange jetting and finds this works. But as the RPM?s increase and the blowback is controlled a dangerously lean condition exists until the high speed jetting takes over.
This is why it?s not good practice to hold the throttle to long in one position!

In an effort to prevent some of energy loss from the stopping and starting the fuel charges and the disruptive nature of pulling a charge from a hostile environment all kinds of open plenum intakes or equalizer intakes have been tried.
I have seen so many mathematical equations for volume; length and port timing unfortunately unless you run at just one rpm (drag race) they really don?t work very well.

To summarize ??equalizer intakes. Open plenum intakes are designed to help with the energy loss from starting and stopping fuel charges and to provide a more stable environment to pull the charge from, aside from a small widening of the sweet spot,
They really don?t help with the rich midrange caused by the fuel charges being pulled through the carburetor three times

oscar89 · Post by **oscar89** » Tue Feb 17, 2009 9:49 pm

Please, definition of the technical term; blubbers?

S_Kyle · Post by **S_Kyle** » Tue Feb 17, 2009 10:00 pm

I believe he is referring to the spitting of fuel out of the the carbs at low speed. Most notable on the 00 Deere's when the air box is removed.

JD600 · Post by **JD600** » Tue Feb 17, 2009 10:22 pm

My 600 does that. Is that concidered somewhat normal?

oscar89 · Post by **oscar89** » Wed Feb 18, 2009 1:16 am

Yeah ok thats the cloud I see at the mouth of the carb. Thanks.

Joliet Jake · Post by **Joliet Jake** » Wed Feb 18, 2009 3:49 am

Touch? ?????I sometimes forget to explain ????.but I believe S kyle and you have nailed it!

S_Kyle · Post by **S_Kyle** » Wed Feb 18, 2009 4:02 am

Glad I could help for a change.

JoeRainville · Post by **JoeRainville** » Wed Feb 18, 2009 10:54 am

Jake and Guys,

Nice job explaining blowback and reeds and such. Been kind of busy with my VC sleds and such!

Next up: explaination of case reeds vs. cylinder reeds...

-Rainville