'87 GSXR1100 Front-End with 70's GS "star spoke" 19" Mag?

[twist-throttle]

Summary:
What complications would I need to resolve to fit a stock late 70's GS "star spoke" 19" mag wheel to a '87 GSXR1100 front-end?
My thought is the brake rotors to caliper alignment will be the most likely challenge. I have attached a pic of the forks.

Full Post:
I'm asking about the logistics of doing the installation, hopefully not beginning yet another debate about which suspension upgrades are best.

My bike is a '77 GS750 with a laced wheel & a single front disk brake.
At my local salvage yard, I have come across a near-complete '87 GSXR1100 front-end. It is only lacking the front axle & spacers (I presume that they have it elsewhere, I just haven't asked yet), front fender & the left handlebar (the actual clip-on mount is on the fork tube, just not the handlebar), well & the '87 GSXR brake rotors haven't been asked about yet either.
It does include; both triple-clamps, complete forks, both calipers & the master cylinder. They dropped from $400 to $350... would you consider this to be a fair price? The setup is dirty from sitting, but looks quite clean & damage free. I spotted a few spots of surface rust on the tubes... but they all seemed to rub right off with my finger.

I believe that it would just be a bearing swap to mount the triple-clamps into my 750's frame, as I've seen pics of other '87 GSXR front-ends on the GS's.

But it's the brake rotors aligning with the GSXR1100 calipers that has me wondering... Plus will the GSXR rotors mount to a late 70's GS "star spoke" 19" rim?
I don't know if the GSXR rotors would dish in or out to much, where my stock GS rotor is quite flat or flush, with very little counter sink... for lack of better description.
I figure that I'd need & want to use the GSXR rotors, instead of trying to use GS rotors?
I do not yet know the diameters of the '87 GSXR1100's rotors or the single/dual disk GS's rotors diameters.

I do believe that the first generation GSXR's did use the same axle diameter as the GS, so I'm thinking that the longer GSXR1100 front axle will work fine with the old GS rim?

Yes, just using the matching GSXR1100 rim would make this a simple drop-in... but at this point, I'm researching the appropriate rims for the bike still.

My ballpark measurements have my stock GS fork tubes to be 31 3/4" in length... from the center of the axle up to the top of the tube, not counting the caps on top of the forks.
These '87 GSXR1100 forks measured about 30 1/4" in length. Neither of these measurements are exact, but I believe them to be within around a 1/4" + or -. So that puts these 41mm forks at around 1 1/2" shorter then stock.

I did also find these forks & measured them while I was there, again, not exact measurements:
'99 GSX750 28 3/4"
'05 GSXR600 28 1/8"

Oh, while the GSXR forks sat there, I did measure the distance in-between each fork leg, where the axle will run through, & where the spacers would push up against the fork tubes... it measured 6 1/2" apart. I do not have any GS measurements like this.
Also, I measured the GSXR1100's front rim that I found... the total width of the rims center hub is about 4 7/8" inches wide. The width of where the GSXR rotors mount to, that is 3 7/8" wide.

Thanks for reading all of this & even more for offering your thoughts about what it would take to make this installation happen.

[twist-throttle]

With a little more research, I now believe that my '77 GS axles are NOT the same diameter as what the '87 GSXR1100 axle would be.

I believe my GS axles are;
Front 15mm
Rear 20mm (not related to Front-End question, but included for knowledge)

'87 GSXR1100 axles are;
Front 17mm
Rear 20mm (not related to Front-End question, but included for knowledge)

With that, I don't see how the GSXR axle would even fit within the original GS rim.
I could possibly use the original GS axle & put some spacers in there to take up the size difference in the forks... but I would sure think that the GS axle is to short, as the GSXR forks must be spaced wider to accommodate the wider front rim, & wider dual-piston calipers.

Still, I figure that this doesn't mean it can't be done... just more knowledge & research thrown at it. Of course going to the 18" GSXR wheel would be a simple drop-in...

[jed.only]

GSXR rotors are 5 bolt, 70's GS wheels are 6 bolt for rotors.

[twist-throttle]

Ah yes, more pieces to the puzzle.

Thank you very much for this reply, that proves that I'm not going to run the GSXR rotors on the earleir GS rim.

I guess another reason (if I do decide to go with the '87 GSXR1100 front-end) to just use the matching 18" GSXR rims.

Thanks again for the reply & pics.

What do you all think of the price of $350 for the GSXR1100 front-end... with the missing items that I mentioned in the first post?

[SqDancerLynn1]

If you want to replace the front forks? The best way is as a complete assembly or at least compatable years so that you get the better 89GSX brakes!!

[dardoonk]

With a little more research, I now believe that my '77 GS axles are NOT the same diameter as what the '87 GSXR1100 axle would be.

I believe my GS axles are;
Front 15mm
Rear 20mm (not related to Front-End question, but included for knowledge)

'87 GSXR1100 axles are;
Front 17mm
Rear 20mm (not related to Front-End question, but included for knowledge)

What is the outer diameter of each bearing?

[twist-throttle]

What is the outer diameter of each bearing?

Sorry, I do not know, I didn't measure these myself, I just found these numbers in a post on this site. Also, my bike is still tucked away for the winter, so I am not in a position to measure these.

[posplayr]

A few points

Here is what I'm doing to put 1st gen forks/wheels/rotors and brakes onto a GS1100ED. Mixing and matching GS/GSXR wheels and brakes kinda defeats the purpose of the swap (better radial rubber, better brakes, as well as stiffer forks).

The 86 GSXR 1100 forks have 15 mm axles while the 87-88 are 17mm. You would need to increase the ID of your star rims bearings I guess and sort out the spacers.

If you go clipons then no need to worry about handle bar clamps; you still need to weld steering stops and figure a way to mount the clocks.

Can't make any recommendations on how much offset you will have on the rotors and you wlll probably spend $100 on caliper brackets.

It would be easier to pic up the 1st gen wheels, black them out and be done with it. The 3 spoke 18" 88 1100 wheels are harder to come by (I have been cornering the market on them).

http://www.thegsresources.com/_forum/showthread.php?t=135919

Pos

[twist-throttle]

Here is what I'm doing to put 1st gen forks/wheels/rotors and brakes onto a GS1100ED. Mixing and matching GS/GSXR wheels and brakes kinda defeats the purpose of the swap (better radial rubber, better brakes, as well as stiffer forks).

The 86 GSXR 1100 forks have 15 mm axles while the 87-88 are 17mm. You would need to increase the ID of your star rims bearings I guess and sort out the spacers.

If you go clipons then no need to worry about handle bar clamps; you still need to weld steering stops and figure a way to mount the clocks.

Can't make any recommendations on how much offset you will have on the rotors and you wlll probably spend $100 on caliper brackets.

It would be easier to pic up the 1st gen wheels, black them out and be done with it. The 3 spoke 18" 88 1100 wheels are harder to come by (I have been cornering the market on them).

http://www.thegsresources.com/_forum/showthread.php?t=135919

Pos

Thanks for the feedback, yes, since this afternoon & with my continued research, now I am beginning to sway towards the idea of just running the proper 18" '87 GSXR1100 rims. They should look relatively stock'ish, well at least to those that don't know much about it... plus then I'd get wider rims which is good. But I like the idea of not loosing any more ground clearance with staying with a 19". As these forks are a little shorter then my originals.

What do you feel about the $350 price? If you think it's high let me know, I don't have any ties with this particular salvage yard, no hard feelings if you say it's too pricey.

Well thanks again for the reply.

[makenzie71]

Get the bearings for a GSXR1100 (17X42X13) and put them in your GS wheel. You'll also need the inner bearing spacer from the GSXR1100 front wheel...and HOPE it's longer than your old GS so you can trim it down to fit...trimming "up" is pretty difficult. If the GSXR spacer is too short you'll have to go out in search of enough of the right size washers to properly space it or have a machine shop cut you a new spacer or a shim you can stack on top of your stock spacer to span the length properly. I don't think you'll have any issues.

Brakes...good luck. You can run your old GS rotors but you will need some interesting hangers to get the calipers down there.