[GP125] All that you wanted to know on Aprilia RSA 125, and more, by Mr Jan Thiel and Mr Frits Overmars (PART 3) (Locked)

Yes I have an engine here, you may have seen it, attached to a gyrocopter. I've finally got the ballance sorted ( using a counter rotating shaft) so now I'm running a set of chambers, they don't crack now that it runs smooth! BUT there is a flatish spot just before the power, I thought I might try your trick with the valves . I already have a ballance tube between the reed blocks ( carb side ). The last thing you need in an aviation engine is a pronounced power band. Unfortunatly it does not have a power valve. The next set of cylinders will !

uniflow a écrit:

Yes I have an engine here, you may have seen it, attached to a gyrocopter. I've finally got the ballance sorted ( using a counter rotating shaft) so now I'm running a set of chambers, they don't crack now that it runs smooth! BUT there is a flatish spot just before the power, I thought I might try your trick with the valves . I already have a ballance tube between the reed blocks ( carb side ). The last thing you need in an aviation engine is a pronounced power band. Unfortunatly it does not have a power valve. The next set of cylinders will !

Alright, you've convinced me, Ill give it a go.

Unless anyone else can think of a reason why a butterfly valve controlled interconnected header pipe on a 180 degree twin wouldnt work??

williamsmotowerx a écrit:

Daniel A, sometimes the load of the dyno gives you false graphs. Especially when the engine is so small like an 80cc at the lower RPM's.

Have you field tested it to see if that dip is really there?

Of course, it's always there, also on the road.

And only the combination of a lot of ignition advance AND a boost bottle seems to solve the problem. But I will do some more tests after the weekend.

Regards

Daniel A. a écrit:

18mm

Ok. I sometimes had similar power issues if I had a too small diameter, but 18mm in my opinion is ok.

At first i would try to make the exaust a little bit longer and try a smaller carburator.

Jannsen

Frits Overmars a écrit:

Monday morning cylinder.

So it becames lazy

uniflow a écrit:

Jeram, can you use these valves to just join the two pipes together at the headers at low speed. Like a two into one chamber then shut them off at high speed? Save using boost bottles.

A la Kawasaki KR250 tandem twin,it works some

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Wish they haven't abandoned multicylinder roadracers so soon,they did some beatching bikes

Yes they should get back into rotary valve twins!!!

motoholic71 a écrit:

uniflow a écrit:

Jeram, can you use these valves to just join the two pipes together at the headers at low speed. Like a two into one chamber then shut them off at high speed? Save using boost bottles.

A la Kawasaki KR250 tandem twin,it works some

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Wish they haven't abandoned multicylinder roadracers so soon,they did some beatching bikes

Nice post :)

Just when your performance modification contains some ingenuity, you see a brochure from 30 years ago with the exact same technique applied!

At least we know it will work now!

The one an only KR(today) with the KVSS fitted the performance with and without is barely noticeable(as the graph says) wonder why KHI changed to 2 resonators on each cylinder on the KR-1

The KR1 had a power valve?

uniflow a écrit:

The KR1 had a power valve?

Only one model kr250
(which is what the pics were)had a ex valve and i have never seen it.http://www.kr-1s.co.uk/forum/viewtopic.php?t=197
Question
If i was to attempt to build my own engine 50mm stroke.
what would be a good place to start with regards to disk valve diameter?
I do have the RSW and RSA diameter and will add it later Still can't find it 120mm ish?
What was the relationship between the RSW disk and the od of the Crankshaft?

uniflow a écrit:

The KR1 had a power valve?

No never did KDX had blade PV and resonator

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The Kawasaki KR-1S had no power valve in the main exhaust duct, but a rotating open/close valve in each auxiliary exhaust duct. One of these valves also connected/disconnected to a resonator chamber bolted the side of each cylinder.

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Thank u Frits.

I hate when people say things they know not of with acertive conviction.Why?
Please use IMHO if u not sure because this here is a BIG major awesome 2 stroke cultural encyclopedia,only afirm hard facts ,no?

As you see the KR1 HAD "powervalves" yes sir not called by that name but by the famous revolutionary KIPS
Very juicy for the era.

This Kawaki was 1 of the faster if not the fastest 250 street roadracer back then,with straight cut primaries,cassette gearbox,2 piece clutch cover,crankcase induction,and I BELIEVE had the crankshaft gears between the cylinders making room for wide transfer tunnrls but keeping a narrow overall width.
Truly racer pedigree.

I think maybe only Honda was already messing with NS R Vtwins but not so powerful?


I find even the previous KR250 tandem twin race replica quite impressive (engine) with its disc valves and is my belief that the use of KVSS instead of KIPS when there was already Honda ATAC chamber and Suzuki SAEC chambers and Yamaha with the vastly superior YPVS,was maybe a case of patents infringement or they didn't like to copy each others?

nowdays mostly all vary port timings

If only Kawa continued throughout the 90s with these 250s and GP racing

The Kawasaki KR250 also used both a reed valve and a rotary valve together for the best of both worlds.
Maybe, Frits has a photo in his collection?


Regards
Allan

motoholic71 a écrit:

Thank u Frits.

I hate when people say things they know not of with acertive conviction.Why?

If only Kawa continued throughout the 90s with these 250s and GP racing

Hate is a very time consuming emotion perhaps you should use your time to read this.
Yes in my defense to my reply to the EX valve. As we were talking of the KR250 as above i assumed likely as did Lozza (2Tinsitute) We were still indeed talking about the KR250
Conclusions are easy to leap too. [Vous devez être inscrit et connecté pour voir ce lien]
Regarding Kawasaki involvement in the 90's mmmm..........They did continue... just with not such as successful design.X09
Suzuki of course tried as well
With the Suzukis Stroud (or was it Crafer) Kokinski and Robinson found them not as competitive with the Honda's let alone the Aprilia's as well.

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motoholic71 a écrit:

I BELIEVE had the crankshaft gears between the cylinders making room for wide transfer tunnels but keeping a narrow overall width.

I seem to recall Jan saying. That the power take off from the center of the crank can cost a bit of HP. I can’t recall how much. I would hazard a guess that may be part of the other reasons (including the space for nice trnsfer passages) for the eventual domination of the v setup rather than the parallel twin in GP racing (packaging and weight distribution considerations not withstanding)

One Design aspect of the Suzuki TR500 and the T500's GT500's etc was their skewed cylinders (or twisted) to allow the wide large air cooled cylinders transfer passages to overlap lessening the vibration as well as the compromise to their shape.Well That’s the theory anyway IMO

GtG001 a écrit:

The Kawasaki KR250 also used both a reed valve and a rotary valve together for the best of both worlds.
Maybe, Frits has a photo in his collection?

Allan

RE the KR250 (street) Rotary valve and reed set up as well as the other Kawa KMX125 set up they are many pics and other stuff from Frits about the Kawa set up on the ESE works engine tuner pages. The 82 AR125 also shared the Reed Rotary valve arangement. Frits hopefully does have better pics though

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motoholic71 a écrit:

Thank u Frits.

I hate when people say things they know not of with acertive conviction.Why?
Please use IMHO if u not sure because this here is a BIG major awesome 2 stroke cultural encyclopedia,only afirm hard facts ,no?

As you see the KR1 HAD "powervalves" yes sir not called by that name but by the famous revolutionary KIPS
Very juicy for the era.

This Kawaki was 1 of the faster if not the fastest 250 street roadracer back then,with straight cut primaries,cassette gearbox,2 piece clutch cover,crankcase induction,and I BELIEVE had the crankshaft gears between the cylinders making room for wide transfer tunnrls but keeping a narrow overall width.
Truly racer pedigree.
If only Kawa continued throughout the 90s with these 250s and GP racing

Ummmm the KR-1 DOES NOT have a cassette gearbox. It has a balance shaft under the engine to cancel out the rocking couple forces from a wide crankshaft, that's how they managed to fit decent cylinders on. I own KR-1(and a KR engine ) so I was fairly sure they didn't have a "power valve" as such only KIPS resonators. I'm not sure but the KIPS first appeared with a KX 125 in maybe 85/86. The best system is the GAS GAS that has both resonator and powervalve ........with 3 moving parts opposed to a KDX/KX that has about 300.

I apologize for the use of the word hate,Eng is not my native language so I tend to use commun phrasing which doesn't exactly translate what I mean sometimes.



I was just Reading a banshee related topic where each one is given the freedom to public the most barbaric nonsense and personal especulation as if God's true,so that had me wound before I got here.

Also I miss understood that it was being said the KR1 had no exhaust control whatsoever.
I'll be more careful in the future.
The confusion might come from the fact that the 2 models have similar designations: KR250 and KR1 (also 250)

I do insist on calling that a cassette gearbox as to my knowledge the gearshafts,shift drum and forks can all be extracted in 1 piece by removing a side "Wall"but if I'm wrong or have a missconception excuse me I did reserch it a little
But let me also thank for the pictures of a extremely interesting bike I was not aware of,very impressive machine but should also be an engineer handfull by the looks of it

No need to apologise.

Kawasaki is the poorest of the Japanese manufacturers, lots of times they came up with innovative solutions by clever engineering.

'...A Cassette transmission is one that can be removed, as an assembly, by simply pulling a transmission plate or sidecover, without involving major disassembly of the machine....'

Not my definition of a cassette gearbox, but the KR-1S and KR-1 definitely have a gear box that matches that description of a cassette gearbox. The gear box can be taken out with the engine in the frame. Remove clutch cover, remove a couple of circlips, remove shift drum cover, undo 8 or 9 bolts holding gearbox cover, remove cover with gears and selector drum attached. Takes less than 10 minutes.

Yep that little engine would not be in "shame" at a race track,even the chrome bores were somewhat uncomun on a street bike back then.

Being that the clutch cover is a round piece like MX engines use ,I bet a dry clutch would be quite feasable.

had they built a racer around the very KR1 engine cases I bet it would have been much more competitive back then than the later X-09,and who knows kept them in the game.


I recall Reading about a SP version with 34 carbs etc any one knows or I'm just dreaming?

It's a real shame they retired when they did but hey lend me that X-09 and I promise a bunch of amateur racing podiums

Sorry for off topic

PS just to close this the kr1 was the fastest 250 of 4 (nsr,rgv,tzr) and held speed record for 250 production machine at Bonneville.The Kr1-r had 35mm carbs and a close ratio box to compete in SP and seems that a full F3 kitted bike puts out 68HP!!

OK I'm out

motoholic71 a écrit:

held speed record for 250 production machine at Bonneville.

Holds the speed record for 250 production machine at Bonneville

Holds the speed record for 250 production machine at Bonneville

Unfortunately my engine still doesn't work as it should. Even with 40° ignition advance and boost bottle it stutters. I don't know why it worked last saturday, maybe it has something to do with the weather.

Frits, do you think I should try a 19 or 20mm restrictor instead of 18mm?

Regards

Isn't 40º way too much ignition advance?