Rear disk conversion-GT550 Need Sprocket Hub selection help

[Cragdog]

Hey guys,
I am working on mating a GS1100 rear wheel with disk brake to my GT550 swingarm. After a number of attempts at assembling the different parts that I have to get the right spacing, I've found that I can make it work with the sprocket hub from the old drum-brake wheel.




The only issue is the diameter of the drum hub is smaller than the diameter of the housing, and if I use the correct size hub, then the spacing is off because the larger hub extends out about 1/2"-1" with the sprocket.


Smaller diameter/shorter hub, drum brake wheel (left) and larger diameter/longer hub, disk brake hub (right)

This is the larger hub, it extends the sprocket too far out:



I'm trying to source a hub that is a blend of them both, one that has the diameter of the larger hub (18cm), but the width of the smaller one (3.5cm from sprocket mounting surface to wheel contact surface). If anyone has any helpful advice or knows of a hub with these dimensions I could sure use the help. I'm thinking something like this: http://www.ebay.com/itm/SPROCKET-DRIVE- ... 94&vxp=mtr but it's hard to tell because obviously these are described as the bikes they are meant to fit and not by their dimensions. Any help is appreciated. Thanks!

[tz375]

GT750 and GSXR750 are 180mm OD and approx 60mm from the tips of the "fingers" to the sprocket face. You could probably machine 5-10mm off the sprocket face to move it inwards.

But before you do that, are you 100% sure that the wheels are correctly aligned? I recently fitted a GS drum brake wheel to a GT750 swingarm and it slipped in with stock GT brake panel and wheel spacers. The wheel rims and sprockets both need to be aligned correctly. Start with the back wheel and make sure it is central to the front wheel first and then get the sprockets aligned by spacing or machining.

[Cragdog]

GT750 and GSXR750 are 180mm OD and approx 60mm from the tips of the "fingers" to the sprocket face. You could probably machine 5-10mm off the sprocket face to move it inwards.

But before you do that, are you 100% sure that the wheels are correctly aligned? I recently fitted a GS drum brake wheel to a GT750 swingarm and it slipped in with stock GT brake panel and wheel spacers. The wheel rims and sprockets both need to be aligned correctly. Start with the back wheel and make sure it is central to the front wheel first and then get the sprockets aligned by spacing or machining.

That's a good thought tz, I hadn't really worried about offsetting the rear wheel because I am using the stock swingarm. My thinking was that if I have the wheel centralized in the swingarm and the sprockets aligned properly then I will be good to go. Never hurts to be that much more cautious when dealing with something as important as your wheels. I will double check wheel alignment and make sure everything matches up properly before rolling down the road.

[Cragdog]

Maybe someone can help explain this one to me..


I'm not seeing what the values for "A" and "B" are supposed to be anywhere in the manual. I knew the Clymer would be problematic, but...
All it says is that if the wheels are misaligned by more than 3mm to correct by chain adjusters, no mention of what values should be. I understand there needs to be a small offset on the left side to account for the drive chain as shown in the figure, but how much??

[Cragdog]

GT750 and GSXR750 are 180mm OD and approx 60mm from the tips of the "fingers" to the sprocket face. You could probably machine 5-10mm off the sprocket face to move it inwards.

When you say "fingers" do you mean the six tabs that slide into the rubber dampers?
This is the measurement I need to find similar, 1 3/8" (~3.5mm):

[tz375]

Q1: what does that mean?

A: All that means from the manual is that A must be the same as B +/- 3mm. Try to get closer than that.

People use string and all manner of other devices to get wheels aligned but it's really simple. I got two 8' lengths of square section aluminum from the hardware store and keep them somewhere safe. When I want to check wheel alignment, I place one each side of the wheels and raise the middle with a small box, house brick or piece of wood. Then gently bind the two rear ends to the sides of the rear wheel with bungee cords - tight enough to hold them in place but not so tight that they bend or distort. The forward ends should be up in the air at teh sides of the front wheel.

Turn the front wheel as necessary to get the wheel and the rods parallel. If the gap on one side is much larger than the other, it is because Either the rear wheel is cocked in the frame and one side or other needs to be adjusted with the chain adjusters OR one of teh wheels is offset to one side of the centerline.


Q2: Fingers?

A: yes. Those are the flat parts that go into the cush drive rubbers. Please measure that depth with a vernier caliper or depth gauge. I can't read rulers in odd old world numbering with a parallax error to compensate for It looks like it's about 1.25" or so, but we need a real measurement please.

[Cragdog]

Q1: what does that mean?

A: All that means from the manual is that A must be the same as B +/- 3mm. Try to get closer than that.

In the figure B is much greater than A, that's where I was confused. If the spacing is meant to be the same value on either side why isn't it depicted so?

[Cragdog]

Please measure that depth with a vernier caliper or depth gauge. I can't read rulers in odd old world numbering with a parallax error to compensate for It looks like it's about 1.25" or so, but we need a real measurement please.

Haha, I thought that might bother someone.
1 3/8" was the measurement as best I could eye ball, but you're right I should put the calipers up to it and check again. The problem is that that is how I am receiving measurements from eBay sellers, with rulers or measuring tapes. So I was trying to measure the same way they were achieving their values.

[tz375]

GT750 is 40mm from the sprocket face to the edge of the cush drive. So was the GSXR that I measured but the GSXR had much larger bearing.

[pearljam724]

Richard, is correct. You need to machine down the sprocket hub that fits the wheel hub. But, the rear sprocket will need to align with the front. Otherwise, if it is off. The bike is going to eat chains and sprockets for breakfast. Bad tire wear, etc.. They sell rear wheel aligning lasers pretty cheap all over Ebay and other motorcycle stores. You simply attach the laser to the chain and it allows you to determine if the rear sprocket is aligned with the front. The difficult part will be determining exactly how much needs to be machined off. I would suggest getting it close in small increments. Checking the alignment as you go. The last thing you'll want to do is shave too much off. Then there's no going back. Trial and error. The other option would be, fitting a GS 1100 swingarm to the 550 frame. But, very likely you would need to machine that swingarm down also. Pick your poison. That's one very worn sprocket by the way.

[Cragdog]

So here's an update on my rear wheel conversion:

I have determined that the 1985 GS700E used this same rear wheel, but with the smaller 17mm axle as was used on the GT550, the wheel I have is the same mag, but is off a 1100e and had a larger axle. I am currently shopping around for either the 700-specific rear wheel or I need to order the smaller 17mm ID axle spacers and bearings then go from there.
Such as:
http://www.ebay.com/itm/350766553969?ss ... 1423.l2649
or
http://www.ebay.com/itm/251259255319?ss ... 1423.l2649

[Coyote]

To me, the solution is simple. Just take the sprocket carrier from the GS to a machine shop and have it faced off to the thickness of the one off the GT. Then redroll and tap for the sprocket you are going to use if necessary or deepen the hokes and threads that are already there. I am no parts expert, but I seriously doubt you are going to find any 'magical' hub off another bike. You've been fooling around with this way to long. The REAL problem is the swinger o the GS is way wider than the swinger on the GT. So you need to compensate for that difference by machining off the sprocket carrier from the GS. DONE!

[Cragdog]

Chris, I appreciate your enthusiasm! Currently I have put my disk brake conversion on the back-burner however.. I had taken my swingarm and wheel to a friend who was going to do the machining last week, and I realized I was missing a few more elements to the equation. I am still planning on doing the conversion, but for the time being I went back to the 16" drum wheel and have been riding the bike around my neighborhood for kicks. It is seriously such a blast to ride! I don't think I ever imagined how sporty this bike was going to be, it really surpassed my expectations. I am in the process of trying to get it titled and registered, so I think once I get that taken care of then I will go back to my disk conversion plans.
The challenge is more than just sprocket alignment though, I need to center the wheel in the swingarm and align with the front wheel before I worry about the sprockets, that means turning down the caliper axle mount to bring the wheel slightly right in the swinger until it is aligned with the front wheel properly, then compensating for the lost space on the left side with the appropriate sized spacer, then machining down the hub for sprocket alignment. That is going to take some attention to detail on my part and accurate measuring.

[Suzukidave]

I still feel the most cost effective way to go is get a GS swingarm made for the disk , it will have everything lined up and the mount already welded on for the rear caliper torque rod .