Small bore 2 cycle engines.

[1212FBGS]

dirt bike motors such as the banshee have the wrong primary drive ratio so stick to a road or road race motor.... it would be to your advantage to use a multi cylinder combination to take advantage of the overbore allowance. +.020 over 4 cylinders makes a lot more displacement than punching out a single...
kent

[1212FBGS]

i think Larry still has that gsxr250 i sold him a few years back.... ya might be able to talk him out of it
kent

[wobblywalrus]

My experiences with making a race worthy motor out of a street engine tell me it is best to start with a good race motor.

[mj43]

The small Aprilia motors are made by Rotax, the 250cc Aprilia is a Suzuki VJ22 engine. Only 350 is the Yamaha (unless you go back to aircooled, S2 and was it Avenger A7? Kawasaki, Bridgestone or the Suzuki which was just a bored out 250 at about 315cc). Arguably the quickest road 250 was the Kawasaki KR-1S but it wasn't imported in to the States. Having said that a few have made it in past the EPA and DOT and they hold the PP-250 records at El Mirage and Bonneville.

If you go the Aprilia 250 (VJ22) route there are 300cc and 320cc kits available so by simply swapping barrels and heads you can go between 250 and 350 classes?

[Interested Observer]

Ref:  “+.020 over 4 cylinders makes a lot more displacement than punching out a single...”

Actually, comparing a single and 4-cylinder of equal displacement, after taking full advantage of a 0.020” diametral overbore allowance, the displacement advantage of the 4-cylinder amounts to only about three quarters of one percent (0.77%).

In and of itself, this would not seem to be a compelling rationale for choosing a powerplant configuration.

[sheribuchta]

I.O.  is right the advantage is the 4 cylinder has more power strokes at the same rpm    willie buchta

[bones]

Hey Bak
I hope the weslake is legal 'cause I'm hoping to bringing one over this year for BUB.
Hey debgeo
Yamaha made a few liquid cooled 2 strokes but maybe wern't available in the US
LC250/350 Based on RD aircooled engines
TZ250/350 factory road race engine also based on RD engines
RZ 250/350 is what the banshe is based on. There are aftermarket cranks and barrels to take these engines to over 600cc
all are parallel twins
TZR250 started as parallel twin and became a v twin
There was bucket loads of these bikes in Australia and the UK but I dont know about the US
These little engines have great potential.
My RS125 honda went 125 last year and i'm 6'1
cheers Bones

[Nortonist 592]

Hey Bak
I hope the weslake is legal 'cause I'm hoping to bringing one over this year for BUB

Bones,  Bob is pulling your leg.  Wes (minus the T)lakes are 100% legal.  I have one in the Norton and one in the sidecar.  Both are certified record holders with the SCTA.  Don't know BUB rules but I believe there was a speedway engined machine there last year.


By weslake, shot with Canon PowerShot A430 at 2008-11-29

[bak189]

Sorry Bones.......Yes, the Weslake is legal......just giving Nortonist the run around, knowing that what he was using to power his LSR equipment.............and yes, we did have a speedway bike racing with us at the BUB meet last year, they were running against a 145mph record....they ran 144mph. time after time
but did not get the record........maybe this year (2010)

Good to hear from you again, Bones........are you bringing your chair over for the 2010 BUB meet?

Regarding, a small displacement engine....we have had great luck with the Rotax build 125c.c. two-stroke
it is basicly a kart engine....but has been used by Aprilia in their roadracing effort....SO it has been used in a M/C...... thus legal.

[Nortonist 592]

Hey Bob.  I was up at Willow Springs on Sat. for the vintage get together.  Spotted this cute little two stroke amongst the vintage stuff.  Could I hook a sidecar to it and run?


By weslake, shot with Canon PowerShot A430 at 2010-04-25

[1212FBGS]

Ref:  “+.020 over 4 cylinders makes a lot more displacement than punching out a single...”

Actually, comparing a single and 4-cylinder of equal displacement, after taking full advantage of a 0.020” diametral overbore allowance, the displacement advantage of the 4-cylinder amounts to only about three quarters of one percent (0.77%).

In and of itself, this would not seem to be a compelling rationale for choosing a powerplant configuration.

IO
 i think your math is a little wrong....lets take a single cylinder yz250 for example 2.614 bore by 2.830 stroke.... if ya add an overbore allowance of .020 yes the increase displacement would be about .7% now if ya take a 4 cylinder GSXR250 with a bore of 1.929 and add the overbore of .020 its darn near 1% "PER" cylinder or 4% overall increase in displacement on a 4.... definitely worth going with a multi cylinder.... now if ya had somethin with a real small bore and long stroke you'll start gettin up there in percentage change, but my GSXR250 example was a really short stroke...
Kent

[bones]

Bob
Yes we will be bringing the vincent chair ,but it is not mine  it belongs to Terry Prince.
I ran 147 and Terry ran 138 at Gairdner this year
My son and I are building some chassis (the universal chassis) for small 2strokes.We have a yz80,rs125,tz350 and also the weslake.
Was the rz350 available in the US?
Would it be worth bringing a couple of engines over?
I think the guy on the longtrack bike(rear suspension and 2speed gearbox)name was Hammel and is an ex world champion
cheers Bones

[ol38y]

i think Larry still has that gsxr250 i sold him a few years back.... ya might be able to talk him out of it
kent

I could probably be talked into parting with it...

[Interested Observer]

Kent,
Try calculating the displacement increase, not the bore increase.

[sheribuchta]

remember also that you can bore to the top of your cc class then .020 over that ---in the case of the yz 250 you could bore it .025 over and still be ok   ---                                            willie buchta