Texasstar
Can't is a four letter dirty word
Let’s build another one! We have plenty of 20 gauge!
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Texas Two Step Taco
- Thread starter Texasstar
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Let’s build another one! We have plenty of 20 gauge!
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John Murray
Been Around the Block
John Murray
Been Around the Block
A bracket that picks up two or three of the head studs and connects it to the frame. A solid steady stops the frame resonating with the engine and makes quite a big difference to the vibration felt on the bike. Ignore the two jackscrews in the pic, they aren't normally necessary.
John Murray
Been Around the Block
This pics raises a few interesting points - one, the length of the pipe indicates a fairly low torque peak, which makes sense given the limited transfer area of these engines. Two, the large carb, necessary with the limited duration of the piston port intake. And three, the fact that he was able to reach those speeds with limited horsepower, a good illustration of the exceptionally low drag of the old dustbin fairings. Unfortunately they were very susceptible to crosswinds and are now not permitted in almost any type of racing.
Texasstar
Can't is a four letter dirty word
I have an idea that his transfers are highly developed in his engine compared to mine. I found this article https://amcn.com.au/editorial/where-are-they-now-charlie-edwards/
Charlie Edwards and Bert Flood were the guys responsible for Bultacos development of the transfer ports. According to this article Bultaco was so impressed they adopted their design.
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Charlie Edwards and Bert Flood were the guys responsible for Bultacos development of the transfer ports. According to this article Bultaco was so impressed they adopted their design.
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Texasstar
Can't is a four letter dirty word
Texasstar
Can't is a four letter dirty word
We are partial to Dustbins. These are the runs the Bostrom’s did on our cr209 Honda ‘Victoria.’ Take a close look on Ben’s run as he comes over the hump on the back strait at the Circuit of America’s in Austin. https://www.youtube.com/playlist?list=PL-9mHQxrWgU08hxeGLSeDYrDRdhLJ6kyZ
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Texasstar
Can't is a four letter dirty word
John Murray
Been Around the Block
Yes, flywheel mass helps manage torsional vibrations. It also helps get a bike with a lowish power-to-weight ratio off the line quickly, but then once you're moving it tends to slow the engines rate of acceleration through the gears, so it's a trade-off. It also helps with traction where that's a problem, but again it has to be balanced against acceleration.
I used to believe that rotating mass only affected the engines rate of acceleration - ie. a lighter flywheel allowed the engine to accelerate quicker but had no effect on steady-rpm horsepower. But dyno testing showed that a heavier rotating assembly gave a slightly higher peak hp even at constant rpms, and particularly with methanol and methanol/nitro blends. I can only surmise (without any proof whatsoever) that the heavier weight slows the pistons acceleration from TDC, allowing higher combustion temps and pressures to occur as well as more time before exhaust opening. Nitro in particular seems to like this.
Short answer: button rotors are too light for a single of this size, start with a moderately heavy flywheel and test from there.
I used to believe that rotating mass only affected the engines rate of acceleration - ie. a lighter flywheel allowed the engine to accelerate quicker but had no effect on steady-rpm horsepower. But dyno testing showed that a heavier rotating assembly gave a slightly higher peak hp even at constant rpms, and particularly with methanol and methanol/nitro blends. I can only surmise (without any proof whatsoever) that the heavier weight slows the pistons acceleration from TDC, allowing higher combustion temps and pressures to occur as well as more time before exhaust opening. Nitro in particular seems to like this.
Short answer: button rotors are too light for a single of this size, start with a moderately heavy flywheel and test from there.
Texasstar
Can't is a four letter dirty word
So this was an old worthless Femsa electronic ignition that weighed almost 8 lbs and I kept the roughly same moment of inertia on it but removed all the magnets and made it thinner. We will see what it does on the crank. It seems balance on the lathe at 2000 rpms. It now weighs 3.8 View attachment 224960
lbs which is what the Pursang 3.7 lbs and Bandido had. Also put it in the Rotary wheel on the mill and drilled two holes and put two socket bolts in for a remote starter for the left side. Then took harden tool steel Allen and welded it to a socket. That way we can keep the oiled side in oil. Not having to kick this thing over and over is nice during testing. I can always go back to the kick starter once it is dialed in.
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John Murray
Been Around the Block
Looks good. Keep in mind that the chain primary engines also run a flywheel on the drive side, and on the 350/360/370 engines this was quite heavy as well, especially on the Sherpa T. Kinda off-topic but I experimented with lighter flywheels on my Sherpa and found that if I went too far all traction went out the window..
Texasstar
Can't is a four letter dirty word
I switched to a lighter flywheel in between runs one time and with that huge slick it did not want to go. I think the slick may be a mistake. We have used scooter tires to reduce rotational mass on our other bikes and I have a few around here and may switch to a 17” wheel on the front also but then it changes the rake angle. Options. That makes sense about the heavier flywheel and the dwell time BTW.
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John Murray
Been Around the Block
I think you're right about the big slick - if you watch slo-mo footage of pro class drag cars leaving the line most of them will turn the tire half a turn or so before they fully hook up. Certainly worth testing.
Texasstar
Can't is a four letter dirty word
I think it will help with the torsional forces on the clutch and primary. I have been watching the little drag bikes hooking up from Thailand and they know how to hook up a skinny tire. Will eventually build a lighter frame for Taco 2 and use Bert Floods for inspiration.
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Couple of thoughts:
That flywheel is a long way from the bearing and at high revs will cause crank whip which may cause other issues such as cranks snapping like carrots in the same way that TD1 Yamaha motors lost their crank mounted clutches. A double row main bearing the way that many sleds do things might help a little if that's possible to fit.
The windows look a little small unless they only connect to the boost ports. Could be an optical illusion caused by the "bigness" of that piston.
That flywheel is a long way from the bearing and at high revs will cause crank whip which may cause other issues such as cranks snapping like carrots in the same way that TD1 Yamaha motors lost their crank mounted clutches. A double row main bearing the way that many sleds do things might help a little if that's possible to fit.
The windows look a little small unless they only connect to the boost ports. Could be an optical illusion caused by the "bigness" of that piston.