Reeds.. single stage vs 2 stage???

[LakeFever]

Rotax 501. It’s been thirty years and I still remember plain as day which one worked best. Short intake boots and 501 rotary with the fat single pipe rpm max 7700 because belt slip is a bigger problem than peak hp above 7500 or so ( at least it was back then )

back further the formula 1 340 twin pipe rotary made heaps of hp at 11,500 rpm but the clutches were always trouble. You would get that one pass though usually only one per year when everything worked as it should. I can say it seemed impossible that a 340 could generate that kind of speed. Old times seems like yesterday

[Markus]

At 7000 RPM .. that's 117 times a second .. every second . Hard for me to fathom that they open and find their way back to the seated position , flat , no bounce , no doing the wave as the rod comes wizzing past .

Well, pistons move a whole lot further than that. 117 times a second, every second. I am sure there is some bouncing and flutter of the reed valves, just like the rod/rod bolt/piston assembly stretches and compresses.

If you look at reed valve designs, they are very similar from engine to engine. It is probably because the reed and cage of the dimensions used is a simple design that does what it is supposed to do well enough. I.e. open and close and open and close and open and close. Like pistons go back and forth and back and forth and back and forth.__PRESENT

[roadkill636]

What if I put a 0.013" shim between the 0.022" reed and the cage. BEHIND the screw plate?
.hummmm?

[Chaz]

Chicken of the trees alright, I hear iguanas taste the best when you put them in a crab trap for a week, they age nicely into stone crab claws.

Ya killin me brudda ...

Only one hole for scoopin up bugs .. and they gone first day of mini season ..

Just to be clear, Mr. Carson says they close and seal every time .. I say , I "think" they flutter and bounce. One of us has put much more effort into it than the other. Just one of many subject we have covered in the last decade or so .. when I'm able to make it down that way .. I have a place to stay about five miles from his shop . With any luck maybe this summer ..

As stated, the plenum box was surprisingly dry for a wide open throttle , loaded against a test wheel , turn off the key .. and lets take a peek and see.

I have thought about it quite often , two things have came to mind .

Air on the crankcase compression stroke (down) is sent back thru a fairly small rectangle passage and that column meets the reed that's at an angle almost better suited for closing than for opening . Or better said .. that when open , produce a wide lengthwise column , but narrow in width .
I love those spintron machines that have a smoke wand , to see what exactly is going on .. To say cost prohibitive , is a gross understatement ..

The other .. outboards have a pretty poor displacement to crankcase ratio. Take a 3.0L for example. The cylinder is aprox. 500 cc the crankcase is roughly 1500 cc with a wall (rod slot) separating upper and lower portions of the case.
I cant see great forces working to open the reeds , and the same thing to close them . The close side has the benefit of the stiffness of the reed to help it along.

Do I think too much into it .. probably ..
They say knowledge is power .. yea , I'll take a double shot of that ...

Piston speed .. they say 3500 ft/min. is bout it . I know my 700 ci nitrous stuff went over 4000 ft / min every pass .. coatings , better alloy has bumped that up .

Big bore 3.0L with a 3.2" crank ... @ 7000 is right at 3600 (bottom right)

[Whaaaaat]

I thought I remember reading, here probably, a claim that a 2 stroke on full send didn't need the reeds at all? I would think that there would be a rpm range where this could be true. If some sort of harmonic frequency could be reached where the reeds would indeed just flutter.

At full send, is the crank case ever able to reach atmospheric pressure, or is it operating at a negative due to pumping losses (even on pressure stroke)? If this is the case, then ambient pressure outside the reed would keep it open at speed.

[keefallan]

What if I put a 0.013" shim between the 0.022" reed and the cage. BEHIND the screw plate?
.hummmm?

To what end Roadkill?WHy? This is not to question you.....its for me as to understand the why of the shim. OMC has one side of their cages with a shim on all the crossflow motor that I have opened up........and I never understood the why behind it.

[Hupiveneilijä]

What if I put a 0.013" shim between the 0.022" reed and the cage. BEHIND the screw plate?
.hummmm?

Boyesens have like this. Thin tapeslice.

[Markus]

Just to be clear, Mr. Carson says they close and seal every time .. I say , I "think" they flutter and bounce. One of us has put much more effort into it than the other. Just one of many subject we have covered in the last decade or so .. when I'm able to make it down that way .. I have a place to stay about five miles from his shop . With any luck maybe this summer ..

I am sure Ms Chaz will enjoy a summer vacation in a place where they have great reeds.

I think they close and seal every time with some flutter and wobble and bouncing along the way.

The other .. outboards have a pretty poor displacement to crankcase ratio.

From what I remember, crank case compression varies hugely between a 2.5 liter Mercury and a 3.0 liter OMC, but the reeds still seem to be able to do their job on both engines.__PRESENT