Comstars + gsx-r front end

focusinprogress said:
Photobucket really pulled a fast one.....and they won't let me download my albums (over 12yrs worth, 4000 images) to go back and fix every post I've ever made. pretty irritating.

aw man that is a raw deal, holding your pics for ransom. looks like they want $399 to unlock you!

thanks for reposting the pics, sent you a PM...
 
I tried downloading my pics and it didn't work either. Yep, they are holding them for ransom and want $399 a year
 
OK, so I have been thinking about this a lot - and I have to choose a new wheel. I'm considering the old comstar from the GL1000, but am a little hesitant to do so without being able to measure the spoke width. If anyone has a set, some measurements would be great! The caliper spacing is 40mm.

Ideally I would also want to use the matching rear wheel, with drum brake. Does anyone know if that's possible or have you done it before?

I also started looking around at other mag wheels I might like to use, contemporary to my year model. I came across the wheels from The Kawasaki KZ750, same model year (82). I was lucky enough to have a guy working one right next to me in the shop this morning. I measured the the rims and there is plenty of clearance. I assume the process for fitting them would be the same as what has already been discussed here. The only question, similar to above, would I be able to use a rear wheel from the KZ on my CB?

Thanks!
 
front wheel would be similar work yes. According to Partzilla, the rear wheel bearings for the '82 KZ750 are SKF6303 which are 17mm axle......your CB750 uses a 20mm axle.....

The part could be remedied with different wheel bearings, a quick search says 1204 or 2204 bearings are the right SIZE, but I didn't get into looking at load specs.

You'd also need custom centering spacers to run the KZ wheel, and may also have to mill down or add a spacer to the cush drive to get chain alignment.

all in all, not impossible.....but also not just bolt-n-go.

I think I have a KZ mag front 19" wheel kicking around, if you need some measurements.
 
Wish I saw this post earlier could have helped. I didn't read all pages so excuse me if I'm repeating something.

I have a '81 CB750C that I put GSXR forks on. I too wanted to keep the comstars or a mag like wheel too. Mainly because of size and I don't like the look of GSXR wheels on a CB. When I started putting things together it became apparent that there is no way of getting the calipers to clear the comstar bars. I decided to have ISR in Sweden make custom rotors for me with 5 bolt holes, GSXR caliper offset and size, as well as buy an OEM '83 CB750SC mag wheel off eBay. Then I bought a 15mm x 10" dirt bike axel and machined two bushings and a spacer. All in all for me to keep a 18" CB mag wheel, with parts and machining cost me around 500 all in. Custom rotors was the most expensive part but they are very good discs. If your sad about having an 18" wheel over the 19", know that because of the caliper's share line, the 18" barely make it and require a little tie-back if it worries ya. But much better looking than the GSXR 17".

If you want any measurements in creating the axel and rotors let me know.

Good luck!
 

Attachments

  • IMG_9609.JPG
    IMG_9609.JPG
    1.7 MB · Views: 287
Thanks Joseph New York - yes SC wheels was one of the options I was thinking... however i just picked up a GL comstar which is the earlier version of the comstar. JUst got back from vacation, and will be going to the shop tonight to size it up - fingers crossed! They are 19 wheels, and i did notice the share line might be an issue, but I figured I could probably find or have a longer line made if needed.
 
rs_ss350 said:
Thanks Joseph New York - yes SC wheels was one of the options I was thinking... however i just picked up a GL comstar which is the earlier version of the comstar. JUst got back from vacation, and will be going to the shop tonight to size it up - fingers crossed! They are 19 wheels, and i did notice the share line might be an issue, but I figured I could probably find or have a longer line made if needed.
Well the main issue with comstars is the radial calipers clearing the sheet steel, it doesn't even come close to clearing and you can't shim radial mount calipers longitudinally like you can standard mount calipers.

Unless for some reason the comstars you found don't angle out as far toward the axel, but if they didn't I wouldn't imagine they would hold up very well. They are thin folded steel. Or if you had a really old GSXR front end that had standard mount calipers you could shim and space, but I'm not even sure that would pan out without some welding and cutting.

You'll def need a longer share line, my 18" only has 1/2" clearance which scares the shit out of me and I'm working on a longer line or tether.

Cheers


Sent from my iPhone using Tapatalk
 
You could always shim them directly out and use large diameter disc rotors (assuming you don't already ave 320mm?)
 
crazypj said:
You could always shim them directly out and use large diameter disc rotors (assuming you don't already ave 320mm?)
My calipers used 310mm, his could be 320... Yeah, long shim/extenders could be the only only way to get comstars to work IMO, why I didn't do it was because the rotors would have to be enormous and was worried the shimmed extensions would make the mount less sturdy. Plus machining 4 extra long mounting bolts which would cost an arm/leg. I'll def stay tuned if the PO attempts this...
 
If you're going to go through all of that, then might as well use a Buell front end. ;)
 
I'm back! OK, so i test fit the early version comstar on my 07 GSX forks, and the calipers seem to clear just fine. Now I could only really test fit it with the 15mm axle since there's no way to get the 25mm axle through the hub at the moment. so it's a bit of a loose fit, not an exact fit, but enough to decide it might be worth pursuing.

Here's the wheel:
comstar1.jpg


Definitely more clearance. I've taken some measurements, and have questions. Will post my diagram once I've finished it. Any advice on how i might more accurately test fit the wheel would be most appreciated

thanks!
 
Here's the diagram with all the measurments, using the existing comstar 15mm axle as a frame of reference, then a couple of potential options for adapting the 15mm axle. I'd rather use the 25mm gsx-r axle, but the built in collar inside the hub's got a 23.5mm ID, and unless I can accurately and evenly drill that out, not sure it's a good solution.

The solid blue are the bearings. You'll notice there is a slight offset in the hub for the bearing seats, which will lead to uneven spacers.

Please give me any thoughts or advice you got. Thanks!

comstar-gsx-diargam.jpg
 
rs_ss350 said:
Here's the diagram with all the measurments, using the existing comstar 15mm axle as a frame of reference, then a couple of potential options for adapting the 15mm axle. I'd rather use the 25mm gsx-r axle, but the built in collar inside the hub's got a 23.5mm ID, and unless I can accurately and evenly drill that out, not sure it's a good solution.

The solid blue are the bearings. You'll notice there is a slight offset in the hub for the bearing seats, which will lead to uneven spacers.

Please give me any thoughts or advice you got. Thanks!

comstar-gsx-diargam.jpg
What I did was grab this axle:
https://www.ebay.com/itm/222195322827
And machined a left bushing, right bushing, left spacer, and right spacer. Looking at your diagrams I see that you've done your measurements, but if you want I can send you the ODxIDxL of each. Note that no two are alike except for their IDs, and the spacers ODs. With that axel and 4 custom parts your ready to go. Also, I JD welded the bushing to the axel's fixed nut, and for the other bushing, I'm planning on cutting it in half so it clamps the axle when axel grips are tightened.

Finally, I have the spacers up against the bearings and removed the dust guards. If you don't like that idea you just have to work on a more complex solution than the 2 spacers.

Sent from my iPhone using Tapatalk
 
rs_ss350 said:
Cool, if you can send me the measurements that will be cool. I've grabbed that axle. Thanks!

The axel parts from right to left (sitting on the bike) are as follows:

(OD × ID × L)

A) Narrow Bushing
24.9mm × 14.9mm × 53mm

B) Long Spacer
22mm × 14.9mm × 18mm

w) Wheel Bearing
w) Wheel Bearing

C) Short Spacer
22mm × 14.9mm × 14.5mm

D) Wide Bushing
31.9mm × 14.9mm × 53mm


[[ A ][ B ][w]====[w][ C ][ D ]]


Notes:

I used steel for the bushings and aluminum for the spacers.

The overall length of this axle with bolt tightened to lock, is shorter than the GSXR axel by a few millimeters. You can inset it on the right a bit to center. To align correctly I'd assemble everything and spin the wheel tapping here and there to get everything lined up, before tightening the fork clamps. The most important alignment is the rotors to calipers.

Alignment is helped if you JB weld the narrow bushing to the axel on the fixed bolt side.

To make the wide bushing fixed, you could cut it in half like me, or get an A for effort and have threads added to the ID. The ID will obviously have to be smaller and threads needed to match the axels threads. The axels threads would also have to be extended. I have a tap and die to handle all this but I got lazy and rather use a split bushing.

Finally your going to need custom rotors with 5 bolt pattern and offset and size of GSXR calipers. I'll attach my order form if you need to order them made.




Sent from my iPhone using Tapatalk
 
irk miller said:
If you're going to go through all of that, then might as well use a Buell front end. ;)

I was thinking same thing, having 'rim brake' on a Comstar could be pretty neat
Of course, it would be a lot easier to get pre 2008 forks so calipers could be moved sideways. Personally I think radial brakes were/are something of a gimmick. Maybe a few professionals can 'feel' calipers moving around under braking but the rest of us......................
USD forks rely on the large diameter axle for their stiffness, using small diameter axle removes almost all the advantage. Luckily, 'our' bikes are much slower than the sportbikes that the forks came off and almost anything will be better than the original flexie forks fitted
 
Wow, 6 months ago I was looking for this exact info and almost gave up looking to see if others had done it. Nice work! I've got GSXR forks and an 18" mag comstar. I will have to dig out my calipers and verify my measurements against yours. Y'all gave me new hope ;D

I don't really have access to a machine shop. Would somebody here be interested in fabbing up some of the spacers for a bit of $$?
 
diyordie said:
Wow, 6 months ago I was looking for this exact info and almost gave up looking to see if others had done it. Nice work! I've got GSXR forks and an 18" mag comstar. I will have to dig out my calipers and verify my measurements against yours. Y'all gave me new hope ;D

I don't really have access to a machine shop. Would somebody here be interested in fabbing up some of the spacers for a bit of $$?
I can't really handle it for ya, but you can contact the guys that did it for me and see if they will ship. The shop is local to me in Brooklyn, called Yanes Machine Shop http://www.yanesmachineshop.com/ Do great work, have a reasonable minimum, hard to talk to and reach on the phone, easier if ya spoke Spanish.

Another plug is ISR Sweden. They made my custom rotors. They are even harder to speak to, you'll have to rely on email to make the order, and their eMail is almost non-responsivze once your order is made. Also, you have to wire them money converted to SEK. I think mine came to like 4000:-SEC which is like $450. If your going to order, here is their form to download the form below to send em: http://isrbrakes.se/products/brakediscs/custom/ I emailed it to them, but they ask that ya mail or fax it, haha yeah right. Finally attached are the measurements I sent in my order form. IMPORTANT: I entered 26mm for the offset because I measured the caliper offset was 21mm and added 5mm for width. But when I mounted the rotors, they rubbed the inner pads a little, and needed to shim the rotor mounts to center them perfectly. You could offset this by ordering the offset to 22mm or 23mm which would make the height 27mm or 28mm, and this might align better, but I think the option to shim is a luxury and if you went too offset you won't have the option. I ended up adding about 2mm in washers. But its your call. Once the axle is bushed and spaced and you get the wheel and rotors on, wheel spins good, then tighten everything up.
 

Attachments

  • Screen Shot 2017-07-31 at 8.17.31 PM.png
    Screen Shot 2017-07-31 at 8.17.31 PM.png
    68.7 KB · Views: 326
erock85 said:
Here's what I would do:
It appears the rotor center spacing is 132mm. The hub is 70mm on Comstar, from rotor mounting surface to rotor mounting surface. Your rotor spacer has to be 28.5mm on each side to correctly space the rotors in the center of the calipers. Next get some Hayabusa rotors, specs on those are PCD: 91mm; (5)10mm mounting holes; OD: 320mm; ID: 69mm; Thickness: 5mm
Clock the rotor spacing to the Comstar hub spacing on your 28.5mm spacer ;D EDIT: you'll want to countersink the mounting holes from spacer to hub
Then you will need 5mm caliper spacers, cheap to buy or I have a drawing to get them made. I had mine made.

eRock, question on your measurements here for the rotor spacers... since my hub mounting surface to mounting surface is 80mm instead of the 70mm you have, would my spacers need to be 5mm less on each side (23.5mm?)

Thanks!
 
Back
Top Bottom