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How does having fork tubes extend past the top clamp effect the propensity for wheelies? [Full disclosure: every wheelie I've done in my life was unintentional, on road or off.]
Well; and I'm trying not to be a know-it-all but as you have said you are learning and folks on this forum are swapping front-ends back and forth at a prodigious rate. I'll risk me being called out and say that the forks sticking out above the top yoke does not really make the bike pop wheelies. This is because the length of the fork is part of the equation.

A very simplistic way to view this is where the wheels touch the ground are like the pans on a beam scale. If each pan had the same amount of weight then the beam would be level. Half way between each pan would be the bikes balance point. Now if you add weight to either end (either dynamically or statically) you change the angle of the beam and the end opposite where you added the weight will be easier to lift (pop a wheelie/do a stoppie) so you lower the front in the triples (slide the fork tubes up in the clamps) then the motorbike turns more easily (here I do not mean it takes less muscle; I do mean it will often turn-in quicker) , will do stoppies but will often tuck the front. Raise the the bike in the yokes and you put the weight on the rear. Here you tend to loose front bite (thus making it harder to turn, here again we're not talking muscle what you often get here is a motorbike that will run wide on exiting the turn ) but you can pop great wheelies.

How far the forks are proud of the top yoke is only relevant to that pile of parts. The length of the fork from end to end and what the length of the forks that the designer was working with when he first laid out the motorbikes geometry are what is important.

I tell you all this because when one looks at a picture of a bike such as yours (exactly what I did when I made my comment) it's easy to see all that fork tube sticking up and think that thing has no weight on the rear and the rider will be doing burn-outs at every corner. The inverse can also be true raise the yokes up to the top of the tubes and you move all the weight towards the rear. Good traction and great wheelies.

The thing is, because I have no idea how long the forks that came on your bike from the factory were. How far they stick out of the top yoke in your photo has little bearing on how the bike handles. I said they were out quite a bit because that was relevant to what handlebars you could use as the tubes could be in the way of the mounting for the bars.

The fun part of all this is that you have uncovered one of the main aspects of motorbike set-up. RAKE ! If the bike doesn't want to turn or turns too quickly you go back to our balance beam. Lift the rear or lower the front and you put more weight in the "front pan". Drop the rear or lraise the front and you put more weight in the "rear pan". So you can see that if the motorbike is spinning the rear wheel coming off the turns you change the rake one way. If it's going to pop wheelies at the drop of a hat then you can go the other way.

Now remember this is all about degrees of change and with modern suspensions there are a plethora of changes that one can make. Some can be done with the adjusters on the suspension or locating and rake changes others must be done by dissembling the shock/forks and changing the internals.

If you are at all interested in this aspect of building then you need to expand your motorbike library my suggestions are books on set-up by; Lee Parks; Total Control. Andrew Trevitt; Sportbike Suspension Tinning. These tend to be my go-to references if I feel myself starting down a dark handling rabbit hole .

One last recommendation is the Dave Moss motorbike site davemosstunning.com. Here he deals with everything from weather and how it pertains to set-up to riding gear. He will also answer your questions if you e-mail him. Well worth a look-see.

Cheers
 

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Discussion Starter #502
This bikini fairing would be better for wheelies, it's not going to get in the way much and it looks pretty light.
How can you ride a Bultaco and not wheelie, I've never ridden a Bultaco that I didn't wheelie intentionally, I thought that's what they were designed for.
I wheelied my race bike a couple of times at really, really inopportune moments. I endeavored to keep the tire in contact with the tarmac after that.
 

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Actually, if you want to see what a Bultaco feels like with faster steering, just ride a Bultaco trials bike, there are tons of them around still.

Wheelies save lives, it's the only way you can ride a motorcycle over something taller then your front axle, everything else results in a trip over the handlebars.
 

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Discussion Starter #504
Well; and I'm trying not to be a know-it-all but as you have said you are learning and folks on this forum are swapping front-ends back and forth at a prodigious rate. I'll risk me being called out and say that the forks sticking out above the top yoke does not really make the bike pop wheelies. This is because the length of the fork is part of the equation.

A very simplistic way to view this is where the wheels touch the ground are like the pans on a beam scale. If each pan had the same amount of weight then the beam would be level. Half way between each pan would be the bikes balance point. Now if you add weight to either end (either dynamically or statically) you change the angle of the beam and the end opposite where you added the weight will be easier to lift (pop a wheelie/do a stoppie) so you lower the front in the triples (slide the fork tubes up in the clamps) then the motorbike turns more easily (here I do not mean it takes less muscle; I do mean it will often turn-in quicker) , will do stoppies but will often tuck the front. Raise the the bike in the yokes and you put the weight on the rear. Here you tend to loose front bite (thus making it harder to turn, here again we're not talking muscle what you often get here is a motorbike that will run wide on exiting the turn ) but you can pop great wheelies.

How far the forks are proud of the top yoke is only relevant to that pile of parts. The length of the fork from end to end and what the length of the forks that the designer was working with when he first laid out the motorbikes geometry are what is important.

I tell you all this because when one looks at a picture of a bike such as yours (exactly what I did when I made my comment) it's easy to see all that fork tube sticking up and think that thing has no weight on the rear and the rider will be doing burn-outs at every corner. The inverse can also be true raise the yokes up to the top of the tubes and you move all the weight towards the rear. Good traction and great wheelies.

The thing is, because I have no idea how long the forks that came on your bike from the factory were. How far they stick out of the top yoke in your photo has little bearing on how the bike handles. I said they were out quite a bit because that was relevant to what handlebars you could use as the tubes could be in the way of the mounting for the bars.

The fun part of all this is that you have uncovered one of the main aspects of motorbike set-up. RAKE ! If the bike doesn't want to turn or turns too quickly you go back to our balance beam. Lift the rear or lower the front and you put more weight in the "front pan". Drop the rear or lraise the front and you put more weight in the "rear pan". So you can see that if the motorbike is spinning the rear wheel coming off the turns you change the rake one way. If it's going to pop wheelies at the drop of a hat then you can go the other way.

Now remember this is all about degrees of change and with modern suspensions there are a plethora of changes that one can make. Some can be done with the adjusters on the suspension or locating and rake changes others must be done by dissembling the shock/forks and changing the internals.

If you are at all interested in this aspect of building then you need to expand your motorbike library my suggestions are books on set-up by; Lee Parks; Total Control. Andrew Trevitt; Sportbike Suspension Tinning. These tend to be my go-to references if I feel myself starting down a dark handling rabbit hole .

One last recommendation is the Dave Moss motorbike site davemosstunning.com. Here he deals with everything from weather and how it pertains to set-up to riding gear. He will also answer your questions if you e-mail him. Well worth a look-see.

Cheers
The rake and trail figures for this bike have been considered.
Repeatedly.
Extensively.
Ad nauseam.

 

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The rake and trail figures for this bike have been considered.
Repeatedly.
Extensively.
Ad nauseam.

That picture taken at face value make the bikes rake look just about right. I also try to avoid to many corner exit wheels on street bikes. I' told that it can help finish the turn and straighten you out but that's left for better men than I.

As I look at your motorbike Tanshanomi I must say that I kind of fall in love with the things simplicity. Looks as if it might be a wee bit front high but that may just be an optical allusion.

I'd have to make it a ton-up cafe racer but that's nothing more than Old Man craziness.
 

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Corner exit wheelies are the best ! don't know as it straightens you out much (you do that with balance) but it certainly improves traction to the rear wheel.
 

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Discussion Starter #507
That picture taken at face value make the bikes rake look just about right. I also try to avoid to many corner exit wheels on street bikes. I' told that it can help finish the turn and straighten you out but that's left for better men than I.

As I look at your motorbike Tanshanomi I must say that I kind of fall in love with the things simplicity. Looks as if it might be a wee bit front high but that may just be an optical allusion.

I'd have to make it a ton-up cafe racer but that's nothing more than Old Man craziness.
I realize that nobody is going to read through a 500-post thread, but if you go back and look, this bike has been mostly a self-taught practical lab course on how to build a motorcycle properly from the ground up, not a desire to make a fancy "custom." Though I don't want it to be agressively hideous, I have tried to think mostly about the appropriate construction and function of this bike, aided by a lot of really good advice and humbling input from the guys here who have more experience than I have (although, sadly, many of the best of them have disappeared in the 9-1/2 years I've been playing around with this).
 

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Discussion Starter #510
In keeping with my "do a little something every day" approach, I went down to the basement before work and made up a couple of little brackets to mount the front fender. Since the bike it came from (Honda 650 Nighthawk) had a leading-axle fork, and the GS750ES forks aren't, the bolt holes in the fender were too far to the rear and at a slight angle when properly positioned over the tire, so the bracket had to compensate for that. When I was all done, the rear of the fender is 1" away from the tire, and the front is 1.1". Good enough.

It's amazing how much attention it takes me to get these sorts of little details correct.




 

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In keeping with my "do a little something every day" approach, I went down to the basement before work and made up a couple of little brackets to mount the front fender. Since the bike it came from (Honda 650 Nighthawk) had a leading-axle fork, and the GS750ES forks aren't, the bolt holes in the fender were too far to the rear and at a slight angle when properly positioned over the tire, so the bracket had to compensate for that. When I was all done, the rear of the fender is 1" away from the tire, and the front is

It's amazing how much attention it takes me to get these sorts of little details correct.




In keeping with my "do a little something every day" approach, I went down to the basement before work and made up a couple of little brackets to mount the front fender. Since the bike it came from (Honda 650 Nighthawk) had a leading-axle fork, and the GS750ES forks aren't, the bolt holes in the fender were too far to the rear and at a slight angle when properly positioned over the tire, so the bracket had to compensate for that. When I was all done, the rear of the fender is 1" away from the tire, and the front is 1.1". Good enough.

It's amazing how much attention it takes me to get these sorts of little details correct.




Looks good . You might try some aluminum spacers and use ally strap to make the brackets. The reason is that ally will polish up and have a finished look. Does the fender (can't tell from the pictures) have a recessed area to keep the fender from rotating ? If it doesn't then the single bolt will allow it to rotate in the air stream. Just suggestions and things to look out for, yep mistakes I've made.
 

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Discussion Starter #512 (Edited)
Looks good . You might try some aluminum spacers and use ally strap to make the brackets. The reason is that ally will polish up and have a finished look. Does the fender (can't tell from the pictures) have a recessed area to keep the fender from rotating ? If it doesn't then the single bolt will allow it to rotate in the air stream. Just suggestions and things to look out for, yep mistakes I've made.
The fender is held on by two bolts per side. The rear bolts go through the fender's rear bolt hole into the fork legs, as normal.

Also, your posts all repeat the original message twice. You don't have to click both "quote" and "reply." The reply button automatically inserts the quote.
 

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This is a good approach! I need to learn that.
LOL nope I only hit reply and then "post a reply". I'm too old to be good with computers buy I'm also lazy so I hit as few keys as I can get away with. Don't know why this is happening ???
 

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Discussion Starter #515
Rivnuts are my new favorite thing.

I'm working on the shift linkage, which is (of course) way more complicated than you'd expect—because Bultakenstein. A late Bultaco engine's shift shaft has spined ends exiting both sides of the crankcase, which sounds fortunate, but (and these are big buts) the left side comes out behind the countershaft sprocket, and the right side is directly even with the bottom frame tube. Furthermore, they both have limited clearance around them due to the shape of the crankcase castings, limiting how far the original shift lever can be rotated on the shaft splines. You can re-clock it somewhat, but not drastically. So, routing the transverse shaft that the Yamaha shift linkage will attach to is somewhat problematic. There is no convenient location to mount the self-aligning bearings I bought 3-1/2 years ago for my shift linkage crossover shaft. The former footpeg boxes on the frame would be the most logical point, if not for the fact that the the rear engine mount blocks the space directly between these boxes.



With the engine and rearset linkage installed, I played around with the cross-shaft position and decided its best location was immediately forward of the old footpeg boxes, as close to them as possible. If I could have thought far enough ahead, I would've integrated shift shaft mounts into the rear engine bracket assembly. But that ship has sailed. The current best approach is adding a small plate bolted to the box each side and extending forward far enough to mount the bearing flange in the correct position.

Further complicating the clearance issues, the sides of the engine mount assembly are almost flush the frame, with no clearance for any sort of fastener inside the frame. Also, there is a metal reinforcing rod welded into the center of the footpeg box cavity.

What I did have as a starting point were holes that I'd previously drilled in the forward end of the footpeg mounts. Back when I was calculating the swingarm and rear tire alignment, I'd cut off the old footpeg brackets and drilled those holes to temporarily fix the frame in the jig, as seen on the right side of this photo:



So, I sketched up a 2D plate design that will bolt to the exiting hole, and one more toward the rear of the box.



Thus, what I really needed was a couple of blind rivnuts on each side. This is an ideal application for rivnuts because there will be negligible torsional or tensile stress, just side loads. So, I bought a rivnut setter and a selection of rivnuts off Amazon for $45. The two holes turned out to be the precise diameter needed for the M6 rivnuts that came with my setting tool. I’ve mounted one in the existing hole in each side.



[Also, a good close-up of how grody the junkyard Pursang frame really is.]

I was fearful these would be somewhat weak or rinky-dink. But these are impressive, really in there solidly, and setting them couldn’t have been easier or more idiot-proof. I’ll make up the plates next, then drill the second mounting hole once I have the bearing plates attached and I'm assured of the alignment.
 

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Discussion Starter #516 (Edited)
"Bultakenstein" isn't just a clever name, it has come to symbolize the character of this project. One of the central themes of Mary Shelley's Frankenstein is that Victor Frankenstein concerns himself only with the academic accomplishment of creating life, giving no thought to the reanimated being's appearance. The resulting creature is fully functional—healthy, strong, intelligent—yet doomed to an inescapably wretched existence due to his hideous appearance. The parallel was not lost on me as I was assembling the crossover shift linkage this morning.

In this particular case, I needed to create a rotating shaft with splined ends. This is not as easy as it seems, because cutting splines is obviously beyond my abilities. I'd purchased a Yamaha YZF600R shift shaft, so I had a proper splined shaft to fit my shift pedal linkage, but it was neither the proper diameter nor the right length for the crossover shaft. Simply cutting off the splined end to the end of the shaft and bolting it to the end of my 10mm shaft would not provide a positive coupling, allowing the end to rotate on the shaft and thus negating the whole point of the splines. Finally, after some extended mental gymnastics, I came up with this arrangement:



The idea is that center of the splined end is threaded, not just drilled. The 6mm stud is firmly seated in the shaft, and the splined end is threaded onto the stud. In this way, the splined section can only rotate on the shaft by crawling up the threads, backing away from the end of the shaft. This is prevented by the lock nut, effectively locking everything together. A bit of red Loctite can be added for extra assurance.

I bought some M6 threaded rod, firmly bottomed it out in the shaft's threaded end hole, and cut it to length. I then hacked off the splined section from the Yamaha shaft. On the lathe, I bored it, tapped it to match, and faced the end square.



I then bolted everything up to see how it went together.

The only way to keep the linkage rod from fouling the pedal was to flip the forward linkage, so the rod end bearing sits inboard of the pivot clamp. I first made a spacer sleeve for the shaft, but then realized I could simply mount the shaft bearing to the outside of the alloy mounting bracket. At that point, it all went together properly, if not elegantly:



The result is somewhere between clunky and hideous. I am afraid that when I get all done with this bike, all of my distasteful, awkward, compromised details will add up to a truly gruesome-looking motorcycle. But, like Dr. Frankenstein, I am willing to pursue whatever path will result in a functional whole from random dead parts...even if it's grotesque.
 

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Discussion Starter #518
I was going to use the splined arm on this R6 clutch actuator and do the same procedure for the other end of the cross-shaft. Fat chance. Hardened steel—ridiculously hard. My carbide-tipped tools barely scratched it.

 

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Discussion Starter #520 (Edited)
Playing around with the shift linkage, I am taking the recommendation of some folks on the ADV Rider forum, and going back to how I had configured it originally, with the bearing mounted inside the plate and the clamp oriented so the spherical joint is facing outward. This makes the whole thing narrower overall, and looks just a tiny bit less bodgy. Or at least it will, once I strip the oil-soaked paper templates off the mounting plates.

The issue with this is that the linkage arm fouls the end of the pedal. I am just going to put a bit more kink in the pedal arm to move the toe end outward a bit. It won't take much to clear it.

Moving over to the right side of the bike, I manged to mate the YZF600R brake pedal to the brake rod of the GS450T drum.

There's only about 4 mm clearance between the brake rod and the shock, but that should be enough. The spherical joint and turnbuckle are from a Ducati 620 Monster.

I cut the bracket from a pre-bent piece of 7/32" steel plate. Nobody will ever call it beautiful, but it works. I stomped down on the pedal pretty hard, and the first thing to flex was the pedal itself.

On the right side, you can see the opposite end of the gearshift cross-shaft, and the pedal stub it will connect to. More parts for this are on the way, but won't arrive for another week or so.
 
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