Kawi2strokes.com Forum

I "believe" the last Aprilia (maybe KTM?) 250 GP bikes were rotary valve. Flat rotary vale flat behind the cylinders, one valve for both cylinders, (opposed port) very cool design. And they were fast! The Konig was like that also.

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Twist the throttle, tilt the horizon, and have a great time. What triples are all about...........

Aprilia RSV250 has one disc valve per cylinder and two geared cranks IIRC. I'm not sure what was in the RS250A or W. They may have been different.

Is that reference to two ports like downward facing boost ports into the crankcase or two connections to the main transfer ports?

That's the one. I got it confused with the Konig.

And it is ports down into the crankcase, not the Boyesen ports that run into the transfers. I messed with them in 94, but didn't feel the extra work was worthwhile.

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Twist the throttle, tilt the horizon, and have a great time. What triples are all about...........

teaser, yes, two just like the ones above, going down into the crankcase chamber. The application is, when the crankcase turns pressurized, mixture has to migrate through the slots in the piston, then, change angles, takes time. The upper and lower extra transfers use the mixture in the rest of the inlet port as a boundary layer, with flow paths up the cut away's, as one directed flow path, no motion transfer through a port, just smooth flow upwards.

In the case of the Yamaha TZ750 OW31's we got the cut away slirt pistons from, they had only one port going from the inlet port upwards. We added the lower port into the cases. Those Yamaha cylinders were good to do, as they had about twice the metals in their skirts into the cases than an H2 has. Even when someone ended up "tuning" their engines into oblivion, I never saw one of the Yamaha's drop a cylinder skirt off the barrel from adding the lower port, and I cannot say that it wouldn't happen to an H2 cylinder sleeve, though.

Yes, dual rotary valves for the Rotax V twin powered Aprilia RS250's. I worked on Al Salaverria's RS250 bike, with factory "enhancements" for two full years. Ran well, but had issues in some parts, and electronics were all the time 'very dicey'. Nice chassis, always wanted to build my own engine from scratch for the thing, just too expensive for parts and regular maintenance items, American "distributor" was also a pirate, always over charged all of us that worked them. .

I also raced a mini-hydro eons ago, when I could still swim, and not drown. Mine had a Konig 500 flat 4, single rotary valve flat in a cavity on the "side" of the cases, shaft driven off the "upper" crankshaft, twin barrel type carbs (no slides or throttle plates, just two round slider disks with cut away throttle "valves" in them that opened to a full round passage), fired two cylinders at the same time, the other 180 degrees later. They were fast, had hella hard to rebuild cranks, took 25 tons to split them down first time, rebuilds were a two time deal, then, new cranks were needed.

Did the Rotax have overlapping discs? It's been a while since I saw the pics.......

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Twist the throttle, tilt the horizon, and have a great time. What triples are all about...........

Yes, the V twins, along with the inline Rotax twins did have "overlapping" rotary valve cavities. The cylinders were also offset from one another, unlike the KR250/KR350 engines. I remember that the front cavity was also part of the rear cavity, and sealing was very critical, used a LOT of Three-Bond 1104 on them back then. Rotax used O rings, very thin, that always broke, and/or flattened out, and lost compression in the sealing surfaces. Only thing Rotax did to make the V twin was to literally build a different set of cases in a V configuration, and use all the inline twin parts for the rest of it, cranks, cylinders, pistons, heads, carbs, rotary valves, all that kind of stuff.

That is just one of the reasons I wanted to build my own engine from scratch, and not have to deal with the Rotax stuff. One year I did the Aprilia stuff for Al, I stayed at Kevin Cameron's house and used his shop between a couple of races. I always stayed at Kevin's place between eastern races that only had a week or three between them. Kevin asked what my engine specs were, and I wrote them all down. He sent them to Roberto Rolfo, whom was leading the FIM 250 GP standings, and Robbie asked where I had obtained HIS specs for his engine. I didn't, they all came out of my feeble brain, with only 1/2 degree difference of all Robbie's and my specs, I was conservative just 1/2 degree on rotary valve closing timing. Everything else was the same as Roberto was running.

We went to Laguna that year, no AMA 250 GP race, and Al wasn't allowed to run the FIM GP, so, we both worked for the AMA in start grid stuff, and I went back and forth to Rolfo's pits to help between AMA stuff.

Al's Rotax engine ran great, was a ballistic missile, when it didn't eat small parts alive, and/or nuke electronic parts.

I love hearing these stories. Tech and history in a story.

John

See Tuner,its easy,you just shared a lot with us again !!! Thanks for the insight !!!!!!!!!!

Thanks Tuner.

I have a pair of regular 409-70 or 71, can't remember which now, with those extra central ports in the liners. Unfortunately one of the lower spigots broke through mishandling, so I need to get Millenium to weld it up and re-plate it. They did that on another 409 barrel that broke a rod and took out the lower sleeve/spigot a few years ago.