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Discussion Starter #1
Hello everyone! I do believe this is my first post here, so looking forward to learning much from you all and hopefully helping people out if I can!

Right now I am working on my 1982 Honda CM450C, and building a cafe racer from it. I have done quite a bit of research into the single swing arms, and have chose the Honda Hawk NT650. The lower mount for the monoshock should be very simple, but I will obviously have to design & fabricate a custom top mount. Here are some pictures for my 2 CONCEPTs as of now. Would really appreciate some feedback or new ideas here!

Here is my build thread on "DO THE TON"
http://www.dotheton.com/forum/index.php ... icseen#new

Thanks,
Jared
 

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Discussion Starter #2
I know the orientation/perspective is off on these, but they are just concept drawings...

The yellow lines are welds visible from that particular persepective, and the red lines are welds behind the material.

Maybe option 2 could be bolted on instead of welded? Just exploring options, I think I would prefer welds here.

Let me know what you think!

Thanks,
Jared
 

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Welcome aboard Jared :)
We'd appreciate a post over in "Member Intro's" to let everyone know a bit about you and the bike. Might stick a pin in the Member Map and see where everyone is :D
Welding is your only option for the plate for structural strength.
Might wander thru the "Project Logs" and check those out, even start one yourself. Look specifically for "nerdsports" log
 

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#2 is going to put less shear loading on the welds so that is better.
 

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Discussion Starter #7
Thank you for the info Jim, I am learning a lot these days! I do have another question though...

I have looked up the extensive list of front and rear axle diameters, steering stem bearings, etc. but cannot find bikes listed that are newer than 15 years old! I am working on a fork swap and cant find what set of forks would work with VFR wheels (20mm diam axle). Are there any newer bikes that have a 20mm axle diameter? If not, couldn't I just get bearings from AllBalls with the same ID (20mm) and a larger OD to accomodate the large diameter axle size on the forks?

FYI... I am pretty constrained to VFR wheels on my cafe rebuild because I am using the NT650 Hawk single swing arm and need the offset rear wheel. I would use the Hawk wheels but they look like crap. Also, from the research I've done, a conversion to Ducati or Triumph wheels seems far too involved. Maybe I'm mistaken?

Thanks!
Jared
 

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Discussion Starter #9
I found another problem / challenge!!! So the CM450C has sprocket ratio of 2.00 (17/34) and a chain size of 530. The Hawk NT560 (since I'm using the NT650 single swing arm) has sprocket ratio of 2.75 (16/44) and a chain size of 525.

My issue here is that I cannot find a front sprocket to fit on my CM450 counter shaft that is 525 to match the NT650, and I can't find a rear sprocket to fit on the NT650 that is 530!!!

As far as number of teeth are concerned, I am trying to keep the front at 17, as changing it down to 16 or 15 wouldn't help me with the ratio since I am already increasing the rear sprockets number of teeth. I am trying to split the difference between the gear ratios of the CM450 and NT650 by getting a 40-tooth rear sprocket (these are available, but only in 525). This would give me a ratio of 2.35, which makes sense to me. Still, this is an increase of about 18%... feedback???

Regardless, I still have the problem with the chain widths... any help? Maybe I can get a 17-tooth 525 front sprocket and retro-fit it to match my CM450 countershaft???
 

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Google is your friend ;) "custom made motorcycle sprockets" turns up a number of sources
I would look at your ratios again. You need to try and be close to the original gearing for the 450 engine setup in relation to speed and rpm. www.gearingcommander.com allows you to change numbers and compare different setups to get it right.
 

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Discussion Starter #11
Thanks Jim! Hopefully this will allow me to get a sprocket that fits on the NT650 rear wheel and that has the stock number of teeth from the CM450 rear sprocket (34). If not, I'm sure I could go up a couple teeth, right? The fewest number of teeth I could find for the NT650 was 40, so would that be fine?

I will definitely check out the gear commander website. Looks like I need to research a few numbers to get the calculations going. Should be too hard. Very interesting to me as a mechanical engineer!

Thanks again,
Jared
 

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Increasing the front sprocket or decreasing the rear sprocket raise the speed vs. rpm ratio and the inverse is true. In the case of running a 40 rear you will be running at a much higher rpm for any given speed that normal.
 

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Discussion Starter #13
I understand, that's a pretty well worded and applicable definition. I wish I had another option though. With the sprocket hub the size that it is, I can't go any lower than 40 teeth. I would have to switch my swing arm game plan completely.

The only other option I can think of is try to get a front sprocket with more teeth to get the gear ratio lower and as close to 2.00 as possible. I've read on some other forums that you have to be careful with front sprockets with 18 or more teeth as they start to collide with the casing. You think that may be a viable option?
 

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You might be able to go to an 18 front but that's about it. With a 17 there's @3/8" clearance of the case.
 

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Discussion Starter #17
Progress on my cafe rebuild!!!

I do have one question at this time though. Before I start designing the rear shock top mount, I am double-checking all my suspension geometry. The one thing I am having trouble researching is the sprung mass to unsprung mass ratio. I have the dry and wet weights of my bike, the travel and spring rate of my 2013 Yamaha R6 rear shock (~4.5 inches and 547 lb/in).

But in order to get the right profile of the rear shock top mount pieces, I need to know where the rear shock will be. Basically, I'm trying to find the angle of my rear swing arm with no rider, with rider, and while driving (always dynamic, I realize). Once I nail down the rear swing arm angle, I'll be able to position the rear shock, and design/fab my rear chock top mount pieces.

Soo... Is the percentage of sprung mass about 75%? Maybe 80% That should get me pretty close. Unless some of you disagree, then I'm down to weigh individual pieces that are unsprung!
 

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Discussion Starter #18
Help! Up to my eyeballs in motorcycle suspension geometry!!!

SO... my main goal is to design, fab, and weld in the top mount for the rear shock. But since I have the freedom to make the suspension geometry exactly how I want it, I am hoping to optimize the anti-squat by getting the best swing arm angle, chain angle (top of sprockets), and anti-squat angle. Read this article for some more information

http://www.sportrider.com/tech/146_0404 ... _geometry/

I have also been reading through "Race Tech's Motorcycle Suspension Bible", specifically chapter 5 (pages 82-94). It is really interesting, but I may be too caught up in the details. Ideally, you should have anti-squat at a little over 100%. And to back out from that the swing arm angle and chain angle (top of) is becoming very difficult.

I would like to have a very clean look for the monoshock top mount, i.e. a single mounting hole. However, I am thinking I will have to do this anti-squat optimization by trail and error. Meaning, I may have to weld in a top mount with 2 or 3 mounting holes, just so I can adjust the swing arm angle and chain angle to get the optimum geometry. Seems like an exercise in "trial and error" that I can't avoid!

Any thoughts out there! "longdistancerider" (Jim) I know you won't be able to resist this one!

Thanks,
Jared
 

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There's a good reason this is referred to as a "black art" :? Even with all of the calculations mathematically made for the "perfect" setup there is still some trial and error to be done.
Since we're dealing with mismatched parts it becomes a little more complicated.
Find a complete NT650 and measure the angles of the shock and swing arm in various positions from static to loaded with 2 people on board. That will give you a good idea of the original angles used by Honda. They really are smart people with an extensive library of what does and doesn't work.
For the top mount consider using 2 U channel parts. One will fit the frame and have 4 holes in it with nuts welded to the back side. The other part will match up to the first facing the opposite direction with 4 slots to allow it to be moved up and down as needed and only 1 hole for the shock mount. This would allow for smaller adjustments than having a series of holes and making gross adjustments. When you're done you can weld the 2 pieces together and make it look pretty.
The depth of the sides for the second part would be determined by the shock angle from the original NT650. You want to keep that angle as close as possible to the original so you don't encounter an over/under cam situation which would lock the suspension momentarily.
 

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Discussion Starter #20
Jim - I am having trouble envisioning the top mount connection you are talking about. But from how you described it, I really like the approach. Do you have any drawings or pictures of this? It would really help!

PS, The rear shock I have is from a 2007-2012 Yamaha R6. I have the connection hardware (picture below). Would I be able to use the aluminum double-shear piece on the top (left side) of the shock?

Just FYI, The shock travel is 4.7 inches and the spring rate is 547 lb/in. I have been unable to find the spring rate of my CM450 or a similar bike just yet, but just started looking online today.
 

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