kf6gub

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I see that some two-cycle engines (ZDZ) are of the rotary valve design. How does that work? thx Jim

altavillan

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As the piston travels up into the cylinder it creates a vacume drawing a fuel charge from the carb. At this time the rotary valve is positioned open. As the piston descends it creates pressure in the crankcase pushing fuel mix into the combustion chamber through the ports. At this time the rotary valve is in the closed position. It's a round disc that is timed to be open or closed to it's mated parts.

mmattockx

Just wanted to add, the disc is attached to the crankshaft and turns with the crank. It sits between the carb and the cases, controlling flow into the cases. There is a window cut into the disc so that during certain portions of the stroke, the window is open allowing flow into the cases and during certain portions the window is closed, preventing flow.

Mark

kf6gub

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Thx, folks. Jim

Tony Hallo

Nobody ask why a rotary valve?
Here's what Two Stoke Handbook has to say;
"The rotary valve still is best in terms of sheer engine performance, whether arranged for maximum performance or ultra-board power range."

Hobbsy

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Front intake engines, as in, (most normal glow engines) are limited by the size of the passage through the crankshaft, the rear intakes can have a much larger opening and a shorter straighter intake passage with more freedom for the timing.

rmh

Also the rotary setuo is th only setup that can provide an assymetric intake porting - reeds can't - non can piston ported types

ALL the perfomance glow engine use rotary vlave -front /rear /disc/drum
piston port and reed valve are easier / cheaper to make and weedies -need only the piston port for their original applications
early glow engines were piston ported

For many flyers the piston port and reed work fine - obviously
if you are into a smooth pipe setup-- the rotary has the most potential
of course any of em done wrong - suck

kf6gub

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Dick Hanson: What performance glow engines use rotary valves for function? thx Jim

Jezmo

Hobbsy, your signature is sooo true!

kf6gub, ducted fan engines and boat engines come to mind although I think there are others.

rmh

any front carb-or rear carb set up has a rotary valve of some type
look at pictures theold engine is a side port /piston port just like the weedie type sold as gas engines today
the front mounrted carb is feeing mix thru a hollow crank with a window cut in it - that is a rotary valve just like almost all small glo engines.

mmattockx

What 2 stroke glow engines DON'T use a rotary valve is an easier question. Are there any out there that use a reed or piston port?

Mark

BTerry

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Most of the Cox engines come to mind...

altavillan

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If "glow engine manufacturers could make a reliable bypass engine work they would. A bypass engine sprays out almost as much fuel as they suck in. And we all know that for "glow drivers" the more mess to clean up the merrier
I'd guess the bypass port design doesn't work well for glow because of a much looser piston fit.

rmh

there are -or were a few
The FOX co in Italy made glow plug singles and twins named TARTAN. took a fair bit of work to get decent power from these
Fro China came the twin called the something Star-
a wretched thing -piston ported a paperweight no matter what was doneto it
The reason most gassers were piston ported , was that the evolution into gassers came thru modified industrial engines and many still do.
Not that they were better but simply because they were available and for the typical recipient, did the job.
If you followed the TOC from mid 1970's thru to the end --you got to see a samping of all the various approaches to getting more power for larger models duning 80's to mid 90's there were various rehashed chain saw approaches in glo and gas - so good some not good.
most of the new stuf from China is a deja vous -(all over again) of the first gassers here -except the ignitions are much better than some early on setups.
All in all I prefer the rotary valve design -
Gee the Baby Bees -I forgot about those things! I still have tho TeeDees 010-020-049-

mmattockx

Good point, I had forgotten about the tiny beasts. How about any that are bigger than 0.25 cuin or so?

Dick, I did think of the Tartan line, but they weren't really very high performance and looked to me to almost be glow industrial conversions.


Mark

rmh

Nope the Tartan were purpose built hobby engines - there were many variants and none were much good till yo u stuck a BIG reed bank in em -

kf6gub

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mmattockx: The two engines Dick Hanson shows are spark plug engines. I have three small glow engines; none of them have rotary valves. I do believe they all have what you called piston ports. Jim