Japanese Bikes, Build Threads & How-To’sBuild threads, tech Q&A and conversations centered around custom-built motorcycles from the Land of the Rising Sun
After a brief build overview of my build during lunch Tuesday, Biltwells Mike D brought up a good point about the rear wheel I have, which is off the same GSXR750 as the front end, and that is the width. I am not a wide-tire guy unless it is necessary to keep the wheelspin in check... this bike is DEFINITELY not that one.
I opted for an SV650 swingarm and rear wheel assy. It is a 4.5" wide rim, rather than 5.5" and the 160 tire width will be much better looking on this build, and easier because the swingarm is very close in width at its pivot. I think a slight mod for axle and appropriate spacers will do it. Once I have both swingarms to compare, I will know what I need to do, but rough measurements were reassuring.
I am retaining a dual-rear shock setup, so I will need to weld some lower shock mounts to the swingarm, but this will also allow me to dial in an improved motion ratio and travel for the shocks. Upper shock mounts may need to change to be sure they are at the proper width. Easy mod.
EW, I took 1.5" out of the middle of the CB750 swingarm that's on my CB450 street tracker. It's easier than I thought, and the axle and swingarm pivot rod make great components for keeping the split swingarm jigged straight during welding. Kutty Noteboom helped me with the aforementioned mod, but I'm confident enough in the process to help you if you need it.
Narrowed swingarms off modern bikes look cool on older iron, IMO.
2 ebay purchases successful with both an SV650 rear whee,l and a swingarm both received and in perfect condition!
Side note: The swingarm pivot bolt likely will not be used because of its intended design for a cast aluminum frame, but it let me know that both the pivot and rear axle are the exact same diameter. Useful info - as a 2nd rear axle may end up becoming shortened and used for the swingarm pivot.
Initial review gives me 2 things to consider, with a couple decisions to make.
1) I need to gain about 1/2" between the swingarm pivot and narrower frame. Halwade had suggested narrowing the swingarm, and I like it, but it brings up other issues that I would rather not contend with. Primarily, the creation of a rear caliper mount that will interface with the disc now that the swingarm would be 1/4" or so closer to the rotor. It is likely that I will instead, modify the subframe in this area and not have to change much else.
2) The new swingarm is about 2" longer. I am unsure I will want to lengthen the bike to that extent. The nice thing about its manufacture is that the swingarm legs were created from an aluminum extrusion and are straight for plenty of distance. The removable axle adjusters are held in place by the axle so I can easily cut-off an inch from the legs without disrupting the slot for chain adjustment and lengthen that slot forward the necessary amount to put the wheelbase where I want it.
Looks like I will be modifying the subframe, as it is much more within my capabilities than welding anything on the aluminum swing arm
I wanted to get an idea that this was going the direction I envisioned, so I stood the rear wheel in the approximate location and put together a before, and current photo.
I deleted my last post, as it became irrelevant after talking with my Dad.
The Great Lars, as we affectionately call him, has put his share of notches on the bedpost of custom bikes and cars. Turning cars into trucks, trucks into crewcabs, dirtbikes into 3 wheel championship ATV's and building show winning hot rods. It would be fun to share some details another time.
After looking at what I am doing, I should have known he would come up with the solution that made the most sense. In its simplest explanation, rather than doing all the cutting and welding I was thinking was needed, it may just boil down to cutting out the crossmember at the base of the frame and widening the subframe with a bottle jack, then weld in a new cross member.
Re-alignment of the axle stubs where they go through the frame may be required, but is much less work than my original plan and should do exactly what I need. There are no motor mounts or frame structure that interfere and the 3 sections of frame that would be affected are easily modified, or replaced with new.
Bearings for the front end will be sorted out and ordered this week!
Looking forward to BF4 this weekend for some killer bikes and ideas! Camera with extra batteries and memory will be on hand for sure.
Tapered roller bearings ordered. 30x48x15 should do it for both upper and lower.
XS frame takes 48mm OD bearings top and bottom, and GSXR stem uses 30mm ID. top and bottom
Once bearings are installed the front end will be secured and I can start figuring out the machining and/or drilling for the top clamp to accept bar mounts!
The front end is installed and I only need to connect brake line to the new m/c and bleed. Heres everything that was required, and a couple things I found to along the way:
I stopped by a friend at Roll Design, who make high-end ATV components, to borrow a press and remove the stem and get the lower GSXR inner bearing race off. Because the GSXR lower clamp is basically flat at the bearing surface, and the outer bearing race of the XS sits up inside the frame a bit, it requires that the lower bearing is approximately 5mm higher when installed on the stem. I used the lower bearing race that I had removed from the XS and flipped it upside down and slipped over the stem to give myself a new surface before installing the new bearing. This works well because both bikes use the same ID lower bearing. I figure this accomplished a few things - it would fit inside of the frame, it was nice and square and I would never need to worry about it crushing or compression over time... plus i had it sitting there.
Slipped it into the frame, installed top bearing and ran into something I had not expected.
The length of the steer tube is perfect, but the threads that exist for the locking spanner nuts that are intended to install above the top bearing are now hidden by the upper bearing. The spanner nuts, and washer between them (with the little tang that settles into the groove) is primarily to allow you to adjust out the bearing slack and not be affected when torquing your top nut. The GXSR stem length, combined with the low profile forged aluminum top clamp still ends with an appropriate amount of protrusion out of the top when fully installed.
I installed the XS dust cap, and top clamp. As it sits, I have full-and-complete purchase of the upper threads with the top nut, and the tapered bearings allow me to torque it and not bind the steering.
So, besides a new steering nut and a bit of safety-wire for security, the front end install is basically complete.
I know what I am doing with the rear end of the bike, meanwhile I am trying to figure out the intake and exhaust.
I want to run a single carb setup.
Here is what I know. I think.:
It took me a bit to figure out how a guy could go from a dual 34mm carb on the XS650, replace the manifold and then run a single 34. Then I realized its because the cylinders pull the mixture on different strokes so it doesn't need a larger carb to flow any more, its just that it is pulling from the single carb more often than before. Quite different than if they were firing at the same time. Right?
Too much carb can hurt performance. This one I am sure of.
Here's the deal. I have a 39mm carb that I REALLY, REALLY want to run on this bike, so here are my questions:
1) If I use a manifold that restricts the volume of air the cylinder can pull, to equal what a 34mm carb would provide, would that allow me to run the larger carb without 'over carb'-ing it? Obviously jetting will have to compensate accordingly. I am ok with the carb not running to its full potential, I just want to know if I am thinking correctly and if I can make this work.
2) Could I use the 34mm ID as my restrictive measurement? What I mean is, if the ID of my carb is 39 and I reduce it to go through a 34mm manifold, would that be the restriction that I need?
My concern is that the smaller ID may actually just flow faster instead of being restrictive.
I would love to hear from people who know something about this so I can be more smarter.
McGoo was very accurate when he warned me about the best intentions and that this would drag out longer than I expected. EDR is only 4 weeks away, nothing like last minute to finish something.
The swing arm became quite a stumbling block. I located a beauty out of Thailand from a company called Motolanna, designed for an SR500. I have a couple spacers to make and it will be installed and a roller. http://www.motolanna.com/ourshop/pro...num-Alloy.html
The seat is underway with Duane Ballard. Seat pan made and foam shaped a few weeks ago to my liking.
The back of the bike is slightly higher than stock, requiring about 1.5" longer shocks, giving it the stance and slightly quicker steering that I want for improved handling. I will use the stock shocks to roll it around the shop, but I will build the correct length within the next 2-3 weeks.
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