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  1. #1
    CB750 Member fingerprice's Avatar
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    spoked rear wheel

    Hi everybody, I'm new to this site.
    I'm building a cafe racer from a 1978 CB750SS.
    I'm looking to modify the hub of my rear Comstar wheel, in order to make a wired wheel.
    Therefor, I need to know the diameter of the pitch circle of the spoke holes of a standard 19 inch rear wheel hub.
    I would also like to know the diameter of the spoke holes in the rear hub.

    Anyone can help me?
    Thanks in advance
    Attached Thumbnails Attached Thumbnails DSC_0010.jpg  

  2. #2
    CB750 Member fingerprice's Avatar
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    The rear wheel is 18 inch, right?
    My mistake

  3. #3
    CB750 Addict losttravlyr's Avatar
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    dunno about the ss comstars but 78 was a 17 inch spokes on the k 's. i personally think for all the hassle attempting to modify and ruin a set of comstars you would be better off getting a 18 spoked from an earlier ss model and then change the sproket dampners to line the rear one up with the front. i think the axles were longer on 77/78's also so you would have to use your old one and you should be able to swap the dampners too.

    comstars were semi ugly but in the long run better than spokes. no rust and 50 less things that could go wrong,,lol.
    losttravlyr,,
    the road goes on forever.

  4. #4
    CB750 Member fingerprice's Avatar
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    Thanks for your reply, but I'll stick to my plan, because I already ruined the rear wheel.

  5. #5
    Daren Daren's Avatar
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    I would be worried that rim was not designed to take the tension spokes can involve.
    The comstars don't "pull" the rim towards the hub, they just brace it. You might have to reinforce them
    which would add weight and possibly make them impossible to balance.
    But I could be blowing hot exhaust out my rear.

  6. #6
    CB750 Member fingerprice's Avatar
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    I understand your comment, but it's not a solution to my request.
    The 'spoke rings' will be made of 316 stainless steel, which is much stronger than the aluminum, which standard Honda rims are made of.

  7. #7
    CB750 Member fingerprice's Avatar
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    The rim will be a standard Honda WM3 rim.

  8. #8
    Daren Daren's Avatar
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    misunderstood.

    Quote Originally Posted by fingerprice View Post
    The rim will be a standard Honda WM3 rim.
    Yea, sorry in an earlier post I thought you mentioned you
    wanted to convert you rear wheel, so I assumed that meant the rim too.

  9. #9
    CB750 New Member MotoSynthesis's Avatar
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    You can order Comstar Spoke Conversion Kit from: http://motosynthesis.blogspot.com/p/shopping-cart.html
    Click image for larger version. 

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  10. #10
    CB750 Member fingerprice's Avatar
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    what is the spoke length I should order?

  11. #11
    CB750 New Member MotoSynthesis's Avatar
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    Depends on your rim and spoke rings. I know what the measurements are for mine.

  12. #12
    CB750 Member fingerprice's Avatar
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    Hey guys,
    Here's an update to my post.
    This is what I did sofar.
    I bought an old 18" 2.15 Honda rim for 10€.
    It will be delivered shortly.

    Since I got no new answers to my questions, I did some calculations, to determine the spoke length, using the formula on this site: http://sheldonbrown.com/rinard/spocalc.htm
    I simplified the formula in an easy to use excel file. If you want this excel file, please feel free to contact me, since I can't share it via this forum.

    some explanations:
    The standard spoke length for a 1976 CB750F rear wheel is 147mm http://www.hondarestoration.com/phot...97686-69134-10
    Number of spokes for the rear wheel is 40
    Cross pattern for all Honda CB750F rear wheels is 2
    Rear Comstar hub width is 45 mm + 3 mm flange thickness = 48 mm
    The only question left is the effective rim diameter. The rear wheel is 18" (18*25,4mm = 457,2mm) minus the nipple dents. Let's assume 450 mm
    With a hub diameter of 230 mm, I get a spoke length of approx 147mm
    So I ordered these 2 spoke rings in 3mm lasered stainless steel.
    Click image for larger version. 

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    When I received the rim, I will update this post.

  13. #13
    CB750 Member fingerprice's Avatar
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    spoke rings have arrived

    Click image for larger version. 

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  14. #14
    CB750 Member fingerprice's Avatar
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    Here's my next update after I received the rim:

    The inside diameter of the 18" WM3 rim is 430mm
    When I use the spoke length calculator with this new value I get a spoke length of 138,8 mm
    Conclusion is that the 1976 CB750F spokes are too long.
    Spokes of the CB750K are 142mm see http://www.cmsnl.com/cb750k1-england...2_42607341000/
    These are correct spokes for the spoke rings.
    When the wheel is complete, I will post a picture.

    Click image for larger version. 

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  15. #15
    CB750 Member fingerprice's Avatar
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    My next update:

    The standard rear spokes for the CB750K are still a fraction too long (less than 1 mm), so I used washers on the nipples.
    It will take some time for the washers to get the correct shape, so remember to regularly check the spoke tension when the rear wheel is in use. It's for your own safety. I think this is still better than ordering custom made spokes, which are expensive. If you go for custom made spokes, order spokes of 140mm.

    About the spoke rings: the pitch diameter of the spoke holes cannot be made smaller, because of the bolts that hold the rings to the hub.
    So the diameters are correct, but I ordered 3 mm thick spoke rings. Better is to buy 4 or 5 mm thick spoke rings.
    Remember to chamfer the spoke holes when you buy thicker spoke rings.

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    Click image for larger version. 

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    The spoke ring is too thin

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    Washers on the nipples

  16. #16
    CB750 Member fingerprice's Avatar
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    Soon I will post the final update.
    I will put everything here to modify your rear CB750F Supersport Comstar wheel into a rear wheel with spokes.
    Since I am deeply disappointed in the reactions to my post, I will silently modify my Comstar front wheel.
    If there are really interested people, they can still contact me.

  17. #17
    CB750 New Member Foyil100's Avatar
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    I really like what you've done here! I am trying to find a '75 or '76 750F SuperSport hub to do the spoked conversion on my '78 750F which has disk brakes but this is definitely another option...Where did you get the spoke rings from? Motosynthesis? If so, how are they holding up? Did they compromise the integrity of the factory hub? Thanks!

  18. #18
    CB750 Member fingerprice's Avatar
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    Hi Foyil100,
    The '75 or '76 750F Supersport had hubs for spokes and brake disc, but these hubs are hard to find, hence, expensive.
    My method gives you a perfectly, technically acceptable alternative.
    I am lucky to work in the petrochemical sector, and our piping contractor has a programmable laser cutting machine.
    I got my spoke rings for free. He had to redo the job, because my initial spoke rings were 3 mm, and they appeared too thin.
    So, indeed, this gave me the chance to experiment. Our contractor was enthusiastic in cooperating.
    The integrity of the Comstar hub is not compromised, because the spoke rings are mounted with the use of the existing 5 bolt holes, that held the 5 Comstar 'spokes'.
    If you want to buy spoke rings, the technical drawing has to be slightly changed: use diameter 217 instead of 215, to get a perfect fit for the bolts. In fact, you only need 1 drawing, because if you look closely, the 2nd drawing is a mirror image of the first one. Also, order 5mm spoke rings, not 3mm. Order these spokes : http://www.cmsnl.com/cb750k1-england...2_42607341000/, probably there are cheaper suppliers.
    I don't know yet if the use of washers on the nipples is really necessary. I still have to mount everything together. Anyway, I guarantee that it will work, with or without washers.
    If you have further questions, I will be happy to give you all answers.

  19. #19
    CB750 Member fingerprice's Avatar
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    mistake, omitted
    Last edited by fingerprice; 08-13-2014 at 02:07 PM.

  20. #20
    CB750 Member fingerprice's Avatar
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    Another thing about the drawing: change diameter 5.3mm into 5.0mm and 8.1mm into 8.0mm

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