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GS 750 Cafe Racer

58K views 107 replies 22 participants last post by  T8erbug 
#1 · (Edited)
T8erbug's GS750 Cafe Racer

I was planning on doing the bike all on my own with no help from the internet world but as I come closer to throwing on the forks, choosing different wheels, axles, and possibly a different swingarm I realize I will need the help and opinions of others to assure the bike comes out working like it should. So let me get you up to speed. Bought the bike from a guy out in Salt Lake. Rode it home so it passed the first test. He had aspired to make it a cafe bike so a few things were already taken off the bike (indicators, seat, misc small items). The carb had air cleaners so that was nice. SO I have started the breakdown of the bike and chopped into the frame. My main focus right now is the tank and you will see why. Feel free to ask whatever and I will fill you in.
 
#54 ·
I haven't posted in a long time but there has been a lot of progress over the last year. It's been slow but steady and things are finally nearing completion. It won't be finished or painted but the bike and mechanicals will all be in order and ridable. Here are some pics of the progress.

Ended up redesigning the rotor spacers to be lighter and better looking. After all was said and done we didn't end up using them but it worked out well because we've been selling them to GS guys all over. They are a conversion rotor to make a GS750 spoked or mag wheel hold a Triumph Daytona 320mm rotor which will then bolt up to a modern GSXR fork and brake setup.


Old vs. New



The use of these parts were not required after some thought and weighing the cost of rebuilding the GS wheels to have lighter and wider aluminum rims. I decided to go all new and adjust accordingly. Warp9 Racing is local and I had them build me these wheels for the bike and they worked out great.
 
#55 ·
I started finishing up the rear frame hoop in a slightly non conventional way as well as tying up some odds and ends. At the time I wasn't sure what clearance issues I might have so I got a 520 chain because of it's narrower profile. The rear sprocket wasn't tough to get but the front proved to be a bugger. Getting an offset 520 front sprocket is next to impossible so I bought a 530 with the offset needed to clear the wider rear tire. 530 and 520 have the same profile just a different thickness so with the help of my buddy Ben we were able to lathe the sprocket down to 520 size.


Here is the first mock-up of the new wheels and tires just to see how things were going to look and to figure out braking etc.


Oh and I forgot to mention I came across a newer gs750 tank for a killer deal so I bought it. I always liked the way they looked.
 
#56 ·
I chose to put 1994 GSXR rearsets on because I wanted to run a rearset with an inboard M/C plus the lines seemed to fit well with what I had planned. The rear brake was intended to be a brembo monoblock unit but after I bought it and mocked it up I realized it would not clear without a spacer so I scrapped that. Instead I bought a stock DRZ400 Supermoto rear caliper and bracket. Worked like a charm. Then it was just a matter of figuring out a torque arm or bracket to hold the caliper in place under braking. Pics of my solution to come later.


The front GSXR monoblock caliper did, however, clear the spokes. It didn't much matter anyways because I had to center both the wheel and the rotor. Once that was done I machined a spacer that would correctly space the two. O and in case you didn't already notice I went from dual front discs to single-sided. There should still be a significant increase in braking power and feel not to mention the weight savings (which is also unslung weight I might add)





New Shock mount installed solid, then cut for alignment purposes. New shocks custom built for this bike by Y.S.S. Fully adjustable compression damping, rebound damping, preload, and ride height. My stock shock mounts were 12mm if I remember correctly as well as bent so I made my new shock mount 16mm.

 
#57 ·
I had the rear end pretty much all buttoned up but I tore it all down and started again. Here are some pics of it all mocked up when it was done the first time. I bondoed the seat plug to smooth out imperfections and make it as symmetrical as possible.


To mount the newer, longer tank on the bike I had to fab up a little bracket. Drilled, tapped, and golden. It works like a charm. The steel was really contaminated so it was tough getting a decent weld on it. Luckily this one is out of sight.


The seat pan after some more refining.
 
#58 ·
Here are some news units for some.. new units.



New brackets so I could install a steering damper. For safety's sake!


Did some swinger work. Decided on a rear brake situation that made a lot of sense. Adjustable side to side and front to back. This basically makes it easier for me to still fudge with my rear wheel/chain alignment without having to mess with a t-slotted bracket like the ones that come from the factory. I still may do that in the future but for now this will work great and is proven.
Here is the torque arm. The one on top was one I made just for mock-up purposes and the one on bottom is the finished product.

 
#59 ·
I know what you're thinking. "Why didn't he undersling the brake or something?" It wouldn't clear between the shock and swingarm which is where I originally intended it to be, so my next option was to undersling it. It looked AWFUL. The way the DRZ bracket and caliper are shaped really made it looked forced/like an afterthought. Where it is now is great because it clears everything really well and will point the brake line straight forward toward the M/C rather than having unnecessary kinks and curves.


ANNNNNNNNNNNNNNNNNNNND back to square one with the tail/shock mounts..


Did a little fixins on the rearsets because they had holes drilled in them by the previous owner



 
#60 ·
The original shift lever and brake lever both had broken toe pieces so I went ahead and found a way to make them bolt up with Warp9 parts :)







Well. . . That brings you all about current with the happenings of the bike. I'm really happy with where the bike has ended up other than the fact it's taken so long to get here. I'm excited to get the tail done. Once that is done I can move onto the body work/rear cowl. Once THAT'S done I can put the engine back in where it belongs and begin finding homes for the battery/electronics.
 
#61 ·
Is there any reason why the pegs are so high and so far back? Like further back than most serious race bikes? Beats me. Why are the pegs so wide?, they could be nearly half as long.

You should get a copy of Engineer to Win, by Carroll Smith. Learn a lot.

There is a reason the manufacturers have long torque rods for rear brake caliper mounts : to spread the stress. Also the torque rod bolts should not be in shear and have a support both sides of where the bolt holds it.
 
#62 ·
The pegs are stock width for a 1994 GSXR1100. They do look slightly wide but unless you feel like making me some shorties for free I think I'll leave them how they are ;) I have done so much fab and cad work on this bike I'm not going to build parts when I can buy parts that meet my needs. It saves me an incredible amount of time and/or money. As for the torque arm being short I have seen pleny of bikes using this setup on front brakes so I'm not too concerned with it on the rear. I did take the shear load on the bolts into consideration during the design process but space issues would not allow for two sided support. With that being said I beefed up the single side to handle the stress load much the same way an engineer would beef up the components of a single sided swingarm. When in doubt, overengineer. Most modern bikes also use a direct brake stay mount that connects the brake bracket directly to the swingarm so as for the stress loads.. I think this setup will handle it all just fine. BUT rather than argue I'm not too proud to report any failures, if any. Thanks for the good advice Witworth. I'll have to give that book a read. I'm going to school now for M.E. so that should be a good read to bring my schooling and passion together.
 
#65 ·
I'm trying to get the tail end buttoned up so my buddy Ben and I can machine a symmetrical plug out of MDF for the rear cowl mold. I had a rad guy help be bend up some great looking brackets for my shock mounts. They fit up very well and I'm pleased with the outcome after tacking it all together. I'll TIG it all up sometime this week and get it finished. I also got my custom brake lines from Galfer on Monday. My rear line had to be re-worked due to a miscalculation on my end. I sent the line in and should have it back this weekend. Finished stripping the tank paint so I can get a few of the little dings out of it and ready for some new paint. Once I can get the tail done I can start finding a home for all of my electronics and battery. I'm going to finish weld the rear mounts, take it apart, get some paint on the bare spots of the frame, and put it back together. It will all be taken apart again this fall and powdercoated once I have shaken it down and made all the necessary adjustments to the rearsets and any other bracketry. Not long till the engine is in and I can mount up my Kerker exhaust and tweak it to make it fit how I want. BUT for now she's a roller again!



Way better shock clearance on this one vs. the old one plus a huge weight savings

Old one

New front M/C for single sided rotor



 
#68 · (Edited)
Hey, thanks I appreciate it. I just got home from welding up most of it. I'm not quite finished welding up the shock mounts but yes I'll be cutting out the center section of the shock mount. I lathed it up in one solid piece because it helps ensure a good solid alignment of both shock mounts. It welded up really nice because the fit was pretty good for the most part. I'm going to mellow out the TIG welds though because they don't match the rest of the welds on the frame. I'll get some more detailed pics. What would you like to see?

490 in the background?
Good eye Keninlowa! You are correct. I have one original 1982 YZ490 and another freak 490 sitting in a 98' YZ125 frame (slightly modified). I'm almost done with that frankenbuild ha and I'm thinking it's going to be a blast.

Not the best pic but it gives you an idea.
This image has been resized. Click this bar to view the full image. The original image is sized 1024x768.
 
#69 ·
Images of the inside after you have cut the shaft out, thanks.

I had to ask if you were cutting the shaft lump out. Nothing surprizes me what people can do when they do frame mods, like leave a big lump of metal there for the tire to hit.

Danger, is my business.
 
#70 ·
Ha yeah, not to worry. I'd like to think I'm a little smarter than the average bear. I like to keep my designs as simple as possible and as close to stock engineering I can. This particular design is very close to stock just beefed up and cleaned up. I used slightly thicker gauge steel for the gussets and made the shock mounts 16mm vs. the 12mm stock ones (which were bent). Weight was also a big factor in the redesign so there was no way I'd leave that big chunk of solid steel in there :) I'll take some pics in a couple of days when I cut it out. I still have some welding to do and don't want to cut it out until I'm done. Frames tend to move under the heat and I'd hate to have my perfectly aligned shock mounts move around on me!
 
#73 ·
Haha well, hopefully my build will be a good representation of my intelligence. It's my first one and I've taken my time with it. No sense in the first flapjack on the griddle always burning :) You'll just have to keep watching the build to see if I do anything stupid haha.
 
#74 ·
I removed most of the paint from the frame so I can do a final fit before I powder coat it. I also need to weld in some tabs here and there for body mounting and such. Got the motor installed again and for the first time in at least a year or more the engine is mounted and the bike is resting on the weight of its own suspension. I'd say I reached a milestone. Now I just need to rewire it and relocate the petcock. Once that's done I should be able to start her up and ride it around!
After the shake-down I'll disassemble it again, make any necessary adjustments, sandblast/powdercoat, and then throw it back together. I'm hoping by next spring it will be 100% complete. But I should have it running in 2 weeks or so.
 
#77 ·
Update

Sorry I have not been here to update more. The build took a major slow down due to a job change and with trying to get myself back to school. The good news is my new job is as a paid engineering intern and I have lots of spare metal and machines at my disposal. No more waiting on people for parts! If I need em, I make em. It's been great and the build is picking up steam again with winter being here. I also sold my little shop truck for $80 more than I bought it for (3 years later) plus trade of a 1981 XS650 in decent shape. Who says vehicles aren't investments!? Anyways here are some pics of the little bit of progress I've made since the last post.

I had to make a new steering damper bracket because in order to fit a headlight where I wanted it the whole unit needed to be lowered. Rather than come up with an entirely new mounting location (which is still a possibility) I machined a new damper mount/steering stopper that would assist in lowering the damper. I then added a spacer for the additional clearance needed. It is surprisingly stout.







Shop truck is gone :( but my original investment of 1K + $80 + 1981 XS650 = One happy camper



I had yet to smooth out the original GSXR top triple clamp after cutting the ignition mount off the front of it, so I built a fixture for it so I could machine the face of it smooth.







I then smoothed out all the cast parting lines out and sandblasted so she's ready for some paint

 
#78 ·
More Updates

The CRF450 M/C I bought to use for the single sided caliper didn't work out for a couple of reasons. Fitment issues as well as just overall condition. Accossato products were on sale during the holidays so I went ahead and bought a radial M/C that should work great with the single sided set-up.



I have had the toughest time finding headlight brackets that would mount on a 45mm fork leg. I'm pretty sure I've only found one or two and I don't really like the styles OR the price so I decided it was time to make some up. They are pretty basic but do the job and have helped me hone my machining skills (which need a lot of work).



I had a buddy of mine at work 3D print a headlight ear that I designed so I could test fit it on the bike. It's just the profile but that's all I needed to get a feel for the angles and lines it would create on the bike once installed.





Turned out looking pretty good so I decided it was time to machine the final product















Hopefully I'll have some install pics tomorrow when I have time to get over to the garage.
 
#79 ·
Got some install photos and just a small update. I pulled the brake line off the front to be sent in for some reworking. Just for better fitment with the new M/C. Next up is finishing my seat plug so I can lay some glass and make a seat.

Some sweet spherical washers I thought would work well with these parts before I built them. They installed perfectly and with a nice snug fit without being too tight aka press fit.





 
#80 ·
Not a whole bunch going on but there has been consistent progress. I was able to open up the back end of the headlamp bucket and hem the sheet metal to make it look like it did before I cut into it. It was necessary to clear the damper bracket better with the headlamp as low as I want it. I sandblasted the chrome and made a nice finish that paint should adhere to. No need to go all the way through the chrome. I am moving onto the completion of the seat cowl/fiberglass work next.





 
#84 ·
I got my brake line back from Galfer the other day so I installed it. It fits great. Spring is prematurely approaching here in Utah and it's got me feeling like the bike NEEDS to be done soon. So, I've been working on what I have been putting off for far too long. The seat plug. I have so many hours in the thing and it's still not done. My method of getting symmetry has changed so I will be documenting that for you guys. For now I have just been working exclusively on the left side of the plug trying, through trial and error, to get the right shape and the best body lines. I almost reached completion of the left side today (sorry no pics) and I should be onto the next steps a little at a time next week. So here are some progress pics from earlier in the week.


Just a little primer to help me see progress and know where my base layer is.


Here is a shot of the line and the underside of the cowling. Just minor changes but they'll make a big difference

 
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