rotary disc valve talk

[k2000x]

ive got a 350 kawaski big horn motor in great nik...have been toying with the idea to use it in a flat track special. now with the disc it opens a port to let fuel in then cuts it off..would it be possible to remove the disc and make a reed block and use a larger carby...mcculloch chainsaws used this system to feed fuel straight to the bottom end so by rights it should work on all motors

[DR]

no simply because you need the disc for the inlet timing. A reed won't do this as it's just a 1 way valve. What can be done is modify the disc as in change the timing of when it opens for how long and when it closes.

[k2000x]

yeah i can cut and modifie the disc....i was just thinking as the chainsaw has one reed on a flat surface. when it sucks to get fuel reed opens letting fuel in..closes under firing load

[Lozza]

That's a brilliant idea, .............if you want to either wake up with a horses head next to you or be looking over your shoulder for the Ninja squad for the rest of your life.
Why would you ever want to buggise around with the perfect induction system?   Reeds don't close because of 'Firing load' they close because the pressure in the crankcase has been equalised.They start to fall about 20deg BTDC.
Want to sell that engine? 

[k2000x]

nah not for sale ive seen how these thing go with some mod's they will eat yz400's thats why i want 2 use this motor for flat track

[Lozza]

Well I might as well dispatch the Ninja's then..................................................

[k2000x]

have you got one lozza...if so what tech mod's have you done

[Graham]

Played with a rotor disk on a miniture road racer YB 100 yamaha,and AC50 suzuki, came across a book call the Chiltins encyclopieda of motorcycles, it was a very early one had all the rotor disk bikes in it.
Had a section on the kawasakis, how much to cut the disk etc.
Also had this neat manifold which has a tuned lenght  around 20 - 30 cm from memory, you take the carb off  and mount the manifold to the case ,then refit carb. I went to the local plumbing store and got bends and joiners to make mine.

It works so well after a race the manifold would have mosture beads on it due to the mixture being cooled
the dense mixture,larger carb, expansion chamber, and total lose ignition made very quick bikes

[DR]

Ram Tube Induction



Mr Springsteen thought the F9 bighorn a good idea too

[Lozza]

Yeah and perenial road race winner Dave Crussell too love the BigHorn. Love how Springer's is eyeballing the photographer to
Done a few disc valvers and they are fantastic engines, as with everything kx it comes down to the intended use and the gearbox, pm your phone number and we'll have-a-chat. Most of those old idea's of tuned inlet length's a mile long have gone out the window.Better way's these days.

[Nitram]

If it's performance you're after- (i.e. spread of power rather than just a raw h/p figure), then your idea of ditching the disc and replacing it with a reed block is sensible.  The disc system is capable of producing great power, but it's always a compromise and a disc that produces good power up top can stumble and have blowback down low.  Not as bad as a piston port engine with it's symmetric inlet timing, but still not ideal. The reed on the other hand guarantees no blowback and will work whereever in the revs that the pipe, transfers and exh port are telling it to.

You are right, there are plenty of high performance kart and outboard motors that use this system.  And indeed the crankcase reed bike motors that I think most racing bikes use now have no piston control of the inlet- it's all down to the reed.

My brother did a disc-to-reed conversion to a Suzuki GP100 in a bucket racer about 10 years ago, and the engineering (i.e. alloy welding/machining) was a bit of a mission ( but nothing that a clever bloke like Loz wouldn't do before breakfast most saturdays  )   Because my brother is a greedy fella, he used a massive six-petal reed block from a YZ490 or something and it was much too big.  The engine produced magnificent bottom end, but nothing up top.  I suspect that the huge reed block had the effect of very substantially increasing his crankcase volume and stifling the transfer pumping at high revs.  Actually that's just a guess.  It wasn't a success anyway and he re-converted it back to a disc with another set of cases.  But the idea was sound, even if the execution was suss.

Incidentally the GP100 cases welded up for the reed conversion are somewhere in my shed if anyone wants them to have a play around.

If you do stick with the disc (and your Big Horn could be made into a real monster with some porting, disc and pipe work) have a read of the Bell Two-Stroke Tuning book, but don't forget the relationship between the disc opening/closing and the transfer opening position.  If you cut the disc and don't time it to the transfers, you'll make it peaky and hard to ride without a c/r gearbox.

Have fun !!

Nitram 

[Lozza]

It took a while...............................................

Oh yes of some interest to you should be the results of a much reconfigured KH 125 is going on the dyno this week. The latest disc shapes have overcome most of the blowback issues as does closing to far after TDC.