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Rear Suspension

This page will show detailed information concerning how I constructed/assembled the rear swing arm/suspension/drive components.

Picked up the parts that were machined for me, the machine shop that I used:
ArrowHead Machine Works (Todd Deahl) : 304-789-6490.
They did a great job at real good price as well!

Here are the parts that they made up for me:

Below shows both of the aluminum rear axle hub flanges and rear brake disc spacer.
After the flanges are welded onto the rear axle hub they will be faced again to ensure that they run true.

Next are the swing arm pivot tube, rear axle shaft and swing arm pivot shaft

Aluminum rear disc spacer, aluminum swing arm head spacer, swing arm pivot bearing holders and rear axle spacers

A better look at the swing arm pivot bearing holders (aluminum)

Here is a picture of the 2 flanges welded onto the rear axle hub. Be careful to place the wheel in the center of the hub, this will vary depending on the offset of the wheel. The flange that carries the wheel gets welded on both sides so when you have the part made be sure to chamfer both sides, while the other (pulley/rotor) flange only gets welded from the 'back side' so only a single chamfer is required.

I MIG welded the flanges as it is *far* easier than trying to TIG weld a flange to a round shaft, one hand to hold the torch. Need one for the filler rod, one foot for the remote foot pedal and nothing to rotate the shaft as you weld it. You could weld a section, rotate it and weld, rotate it and so on, but I think that you get a better quality weld by doing it all in one pass. Make up some simple Vee blocks out of plywood to hold the whole thing so that it rotates easily as you weld, be sure to turn up the juice so that you get good penetration!.

I actually bought 2 rear pulleys, one is a 64 tooth and the other a 71 tooth pulley. It looks like I will be using the 71 tooth pulley to get the desired final gearing ratio, but I have the other one if I need to raise the engine rpm's at cruising speed. Using adjusters for the rear axle greatly simplifies swaping out the rear pulley for a different sized one, it would be a lot tougher had I done the swing arm per plans!! Here is a picture of the 71 tooth pulley.

Here is the rear mono-shock from bike parts dealer, part # PS420-1042 by Progressive Suspension. I also have another spring on order, this one will have a 500lb spring to handle the weight of the rear, I can dial it in when fully assembled, part # PS1165R. This is a pricy mono-shock but has tons of adjustments to it, from spring tension to dampening. My thoughts is that since the rear is controlled by a single shock/spring combo that only the best would do. (The twist ties ensure that the end bushings stay in place.)

I completed fabricating the rear swing arm assembly, I will be using standard style rear axle adjusters, rather than have a fixed mounting point for the rear axle through the swing arm I made some 2" long slots so that I can easily fine tune the adjustment of the drive belt rather than using shims. Right now I left additional material onto the ends of the swing arms and will trim back when finished. I feel even though the use of the adjusters is another modification, it will make the alignment of the rear tire *far* easier than using shimming technique.

Below are various shots of the swing arm assembly so that you can see better the orientation of all of the parts. When you weld this up be sure to have the shock spacer at the upper bracket bolted in place, if not you chance not having the bolt holes align up as welding causes parts to pull and move slightly due to the heat!

I noticed a slight problem with the swing arm when I went to put the axle in place, it appears that since I had not put in the additional side supports yet that as the metal cooled from welding that the ends where the adjusters go had pulled together slightly. This is not a problem as I will make a wood spacer slightly wider than the desired inside dimension, and insert it before I weld in the 2 side braces. This way when the swing arm cools it will be slightly wider than needed in the back, making installation of the rear axle easier. It is better to have it slightly wider because they can be pulled together when you tighten the nuts on the axle, if too narrow it would make it difficult to spread so that the axle can be put into position.

Had to tweak the aluminum bearing supports for the front of the swing arm as the diameters were too large to press into the front tube. Using my mini-lathe I took the diameters down about .005" and put a chamfer on the ends to help start pressing them into the tubes. Then I pressed them into the tube ends and wished that I had taken them down another couple of thousandths as they were still pretty tight, possibly due to welding onto the tube and distorting it a bit. I do not have a large hydraulic press so had to do it the old fashioned way, using blocks of wood and a large hammer... It works but being as tight as they were it took some time to get them seated all of the way.

Here is a picture of the completed brackets for mounting the swing arm onto the engine sub-frame today, making sure that I allowed enough room to clear the round front tube of the swing arm.

Here is a shot of the swing arm dummied up to the engine subframe.

Here is a shot of the rear tire and had it mounted onto rim. It is a Dunlop SP Sport 8000 high performance tire that has directional rotation so care should be taken to be sure it is mounted with the correct orientation. The tire size is P225/50 ZR15.

After going to numerous auto parts stores in my area I finally stumbled into a NAPA store where they actually have catalog pages for wheel studs for the rear axle as the the plans simply call out for 1/2" holes for the studs. Tthe closest one that we found was a 1-3/4" long 1/2 " diameter, .506" at the stud and .530" at the knurl, the picture above shows the replacement #642-1578 (NAPA) wheel stud. So what I will have to do now is to drill the rear axle out to fit the new studs. I purchased a 13mm (.5118") drill bit and redrilled the holes and put in the wheel studs.

I fabricated up the adjusters for the rear axle. Since I made a 2" long slot in the swing arm I wanted the adjuster to cover this area so that it would not accumulate water and stuff in the tubing. So I made them 3-3/4" long. I drilled and tapped the end to accept a 5/16-24 UNF threaded rod and also drilled a hole so that I could pin the rod into the adjuster. All that I need to do is install the threaded rod, pin them and make some back plates to cover the ends of the tubing. Here is a picture of the adjusters along with the dimensions, be sure to chamfer the edges to give clearance with the tubing radius:

Here are the completed adjusters along with the end plates installed on the rear swing arm:

It looks like I will have to modify the shock mounts as my shock might be a bit longer than spec as the side rails should be roughly parallel to the ground once the vehicle is fully loaded, right now they have too much of a downward rake on them. I still need to put the stiffer spring onto the shock, after I make the motor mounts and get the engine into the subframe I can see it fully weighted, then will address this issue.

Here are a couple of shots showing the backend finally resting on the ground.

I reworked the rear shock mount on the engine subframe so that the swing arm was at the proper angle. So I cut off the old one, and ground it down. Next I then set the swing arm at the desired angle, taking into account the amount of movement once loaded, and figured out where the shock end should be located. Then I fabricated new mounts and welded them onto the engine subframe. Since my shock is a bit longer than spec'ed in the plan I moved the mounting point forward and closer to the engine subframe to compensate, you can see the difference before and after in the pictures above and below.

While re-assembling the back end I put on the correct spring onto the shock. The original spring on the shock was rated at 350 lbs, and I also purchased a spring rated at 500 lbs per the plan set. While at it I also put the drive belt on.

When I took off the swing arm I noticed that the aluminum end caps for the front tube contacted the mounts a little strangely. When welding on the gussets the angle iron pulled making the angle slightly off. So I put them onto my mill and milled the face so that it was flat.

Previously on eBay I had purchased 2 steel trailer fenders and needed to cut and splice them together to make a single 11" wide fender. I took a piece of 1/4" thick wood strips and clamped them onto the fenders and using my plasma cut them both. The resulting cut came out very nice and I am extremely happy that I have this tool! Next I brought the 2 pieces over to the welding table and then clamped them together and tack welded them at about 4-5" intervals along the length. Finally I went back and welded them together, alternating between sections so that I did not distort the steel and then ground down the welds so that they were flush. Finally I shortened the fender by bobbing the end about 8" and putting a nice curve on it. Here is the resultant fender:

I took some 1/8" thick 1x2 tubing and cut off so that I had a 1"x2" angle mounts and drilled for a 1/4" bolt. I then put the fender in place and using some 2x4's to hold in place located the mounts and welded them onto the rear swing-arm, and finally bolted the fender in place. Here are pictures showing the mountings and installed fender:

There is an area that you have to tweak to give some clearance for the drive belt, adjust as necessary:

Here is the mounting bracket for the rear brake caliper. I had to profile it a bit as it would have had interference with the caliper.

Here is the bracket welded onto the swing arm. I will need to change the bolts used to hold the pulley/rotor on the axle as the heads of the hex bolts are causing some interference with the brake caliper.

I have been researching brake rotors for the rear wheel. I am not happy with using a flat rotor as it leaves very little space for the bolt heads. It is these bolts that go through the rotor/aluminum spacer/belt pulley/hub that hold the whole assembly onto the rear axle, and right now the bolt heads contact the brake rotor.

This head contact might be also be due to using an 11" rotor vs a 12" one, but regardless there is very little clearance between the bolt heads and the swing arm. The best answer is to use an offset brake rotor, by doing this plenty of clearance can be gotten for the bolt heads.

An offset brake rotor apparently is not a common item for motorcycles, and so far I have found a couple of Honda front brake rotors that might be suitable:

1982 Honda GL1100 Aspencade	1980 Honda CB750	1978 Honda CB400

The plan set calls for the aluminum spacer to be drilled using a 3.250" 5 bolt hole spacing. Above rotor dimensions are unclear but at a minimum they would probably need to have the mounting holes redrilled accommodate to the Harley belt pulley, in addition the aluminum spacer would need to be modified. The rotor for the CB750 and GL1100 appear to be identical. NOTE the CB400 appears to be a lot lighter unit as it does not appear to have the additional steel webbing that attach's the offset hub to the rotor, and thus may not be suitable for the weight of the Vortex.

Spent the first part of the day in taking the spacer that exists between the rear axle pulley and the brake rotor and modifying it for the Honda offset rotor that I previously acquired. Since I already had the rear brake caliper mount welded onto the rear swing axle I wanted the offset rotor to be located in the same location as the previous flat rotor. So I took some measurements with my calipers and decided that I needed to set back the face by about .850". I used the metal cutting band saw to remove about 1/2" to get a rough starting point, it was faster just to cut off the 1/2" section rather than using my little mini-lathe to remove it. Once removed I put the piece on the lathe and turned it down to the final measurements.

Here is dimensional drawing of the spacer:

Here is a picture of the finished spacer:

And with it temporarily on the rear axle:

I had to modify the rear brake caliper mounting bracket. As you recall I modified the rear axle rotor spacer and went with a recessed brake rotor. The diameter of this rotor was larger than the flat rotor that I originally had which caused the mounting holes to be incorrect. I had to 'extend' the top of the bracket and a portion of the lower section as well so that I would have additional material in which to put in the new mounting holes.

In order to modify the caliper mounting bracket I had to remove the rear swing arm, weld on additional material, grind it down as well as fill in the existing holes. Once all this was done I figured out the new mounting position of the brake caliper and drilled new holes:

I had to use a small spacer between the caliper and mounting bracket to position the caliper on the rotor as well. This was planned as initially I purposly made the space between the bracket and the rotor slightly wider than I actually needed. Had I put it even slightly too close then the caliper would hit the rotor, so using a small spacer to shim the caliper to the desired positon makes it easy to put the caliper exactly where it should be.

Once the caliper mounted I finished up running the rear stainless steel brake line to an offset 3/8" banjo fitting and wire tied the line onto the rear swing arm. I am quite pleased with the final results:

Rear Suspension- Done!

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