Wednesday, February 15, 2006

Modified a Mac to fit the 650

The bike is approaching finished now. The biggest mod this time is that I got rid of the 2-into-2 exhaust that I built previously. It was too loud, and since I decided to get rid of the sissy bar there was no good place to attach a bracket to keep it from moving around everywhere. So I shelved that exhaust, and decided to use the MAC exhaust that I had from a parts bike I acquired some time back.

First off, the Mac exhaust for a CX500 will NOT fit on a CX650 without major modifications. The heads are about 1/2" taller, AND 1/2" wider. Add to that an extra 2" of oil pan sticking out the bottom of the engine, and there is no way the exhaust will fit. Fortunately, I have a wire-feed welder.

First thing I did was cut the muffler off of the MAC. The MAC exhaust system comes with the muffler welded in place, and it's a big megaphone that just screams "1970's Honda". Out comes the angle grinder with the cutoff wheel, and the muffler goes in the trash can. Next step was extending the exhaust headers. I cut the headers off about halfway down their length. I bought two exhaust pipe couplers from Advance Auto that fit over the cut-off Mac pipes snugly. Then I took my spare CX650 engine and flipped it upside down on the garage floor. (Note: Make SURE all the oil is drained before trying this!!!) I mounted the exhaust system with the couplers and once it was all in place and looked good, I tack welded the pipes in place. Then I took the headers off the spare engine, put it back upright, and got a bunch of paper towels to clean all the oil off my garage floor.

After I cleaned the oil, I went back and welded the pipes together properly. Then I test-fitted them to the chopper. Well, the bottom bracket didn't line up correctly, so I cut it off and welded it back on in a new location, so it now bolts to the bottom of the engine. Then I tried test-fitting the JC Whitney muffler I was planning on using. It fit perfectly, without any spacers or anything.... but the angle of the Mac pipe was such that the muffler hit the axle and swingarm. So I took the mac off again, and cut through half of the big 2" diameter pipe, right under the engine. I cut a slot about 1/8 to 1/4" wide through half the pipe. Then I bent the pipe to the right, which closed that newly cut slot. Then I welded it back together.

After I was done I wrapped the headers in header tape from JC Whitney, and attached it with stainless steel hose clamps. Then I painted the wrap with high-temp exhaust paint. Then I finally mounted it correctly to the bike, with the crush rings and everything. The muffler bolted right onto the pipe, but there was no support for it bouncing up and down. I welded a stud to the back of the pipe, and used a simple chrome bracket to hold the muffler in place. It looks great.

Now that the new exhaust was on, it was time to correct the jetting. The bike had always run a little lean, so when I installed the 650 engine I also installed #130 main jets. That really helped wide-open power, but it was still hesitant and didn't run well between idle and 4000rpm or so. I rode the bike with my new Mac exhaust like this for a while. I experimented with .020" shims under the needles, and that helped move the hesitation lower in the rpm range. Screwing the pilot jets out as far as they'd go also helped matters. This told me right away that I was running too lean just off-idle. So I repalced the stock #78 slow jet with a #85 slow jet. Instantly the bike ran PERFECT. It's been running that way ever since, though it may be a little rich in the midrange. Going to remove the shims and see if that makes a difference.

Parts Breakdown:
•  MAC Exhaust $Free (got it off a parts bike, been saving it for a while)
•  JCW Muffler $35
•  Misc jets $15
•  Clamps $10
•  Crush rings $20
•  Exhaust couplers  $8
Total $113

Running total for Chopper: $1971

Built Forward Controls!

This is the design I envisioned
The finished product was more elegant than the crude square brackets in my drawing

This linkage worked remarkably well

Not enough room to use Harley ends here, so I welded OEM ends together
The brake side flexed a little. I should have used a beefier rod
The shifter linkage was a straight shot of solid rod, so it didn't flex at all

The brake arm connected to a chopped up OEM brake pedal

Here's the one you've all been waiting for. Foward controls on a CX500. The CX500 is difficult to add forward controls to, because the shifter is rotated 90 degrees from what most other motorcycles. Where a normal bike's shifter rotates forward and backwards (with respect to the bike), a CX500's rotates left and right. For most bikes, attaching forward controls is a simple matter of extending the shifter arm and moving the footpegs forward. Not so with the CX500. Some way to change the direction of shifter movement is required. What's more, the CX500 has no frame downtubes to which one may bolt or weld mounts for footpegs or controls. The engine is a stressed member, and there are no supporting tubes anywhere around it.

My solution is simple. But the making of it was not. I went through many different designs for these forward controls. I started off with trying to use Ace 750 footpegs and levers, but could not come up with an adequate way of mounting them. I tried Yamaha pegs and finally decided my best bet was finding a set of foopegs from a sportbike, where the lever rotates on the footpeg mount. I found some controls from a mid-80's Kawasaki ZX600 on eBay that suited my needs.

I took a 1/8" wall 1" square tubing piece from Home Despot, and welded brackets made out of 1/4" thick 1" wide plate to the bar. The bar mounts to the underside of the engine, on the two unused nubs. I welded bolts to some square blockoff plates, and welded these plates to the end of the bar. Then I used drilled-out pivots from a ZX600 Ninja and welded them over the bolts. The levers pivot on these perfectly, and then a washer and a footpeg keeps the levers in place.

The shifter lever had the tab for mounting a linkage on the top, and I needed it to be on the bottom. I cut it off with my angle grinder and re-welded it on on the bottom. I used some silver paint to protect the cuts, and this blends in with the chrome so as to be almost unnoticable unless you look closely. The brake pedal is made out of aluminum, so I could not cut and weld it in the same manner. But fortunately it already had the tab in the proper place.

Setting up the brake-side controls was easy. I took a stock CX500 brake pedal and cut the pedal arm completely off. Basically I left only the spring mount, stop, and the part with the splines that bolts to the shaft. I then welded on a 2" long piece of 1/4" thick steel so that it hangs straight down, and then drilled a hole in the end. Then it was just a matter of connecting the pedal at the front of the bike with this new lever where the stock pedal used to be. For that I used a pair of early 80's Harley Sportster shift rod ends, a piece of hollow steel tubing from Home Despot, and some bolts from the hardware store. First I bent the bar into shape so that the bar clears the exhaust system and reduces the angle that the harley rod ends are forced into. Then I cut the bolt heads off the bolts from the hardware store, and welded them to each end of the bar. The Harley rod ends threaded right onto the bar, and bolted to the pedal and to the new brake arm I made. I painted everything black, and that was it.

The other side was much more difficult. I knew I wanted to change the forward/backward movement of the new shift lever to an up/down movement. My plan from the start was to make a pivoting "L" attached to the lower motor mount. I just happened to have an EX500 Ninja parts bike lying around, and noticed that the shifter arm was shaped almost perfectly, and had a nice bushed pivot. So I cut the shifter peg off the shifter, and drilled a hole in the end where the peg used to be. I welded the EX500's pivot bolt to my lower motor mount bolt, and bolted the EX500 lever on. I had to extend the EX500 shifter down about 3" with another 1/4" thick pice of steel. To make the linkage between the EX500 lever and the CX500 shifter, I welded together a bunch of EX500 ninja linkage parts. Then I made another rod using Harley ends, and bolted it all together. I gave everything a coat of wrinkle-black paint and that was it. You can see the results in the pictures on the left.

This all sounds easy, but in reality it took me several months to come up with a working design. I went through many different linkage ideas before coming upon one that actually worked, and I wasted a ton of steel and just about every weekend for a few months trying to come up with a workable system. All in all, I'd have probably been better off buying the $550 set of forward controls from Germany. But I have no complaints, these controls work flawlessly.

Parts Breakdown:
•  Square Steel Tubing $10
•  1/4" thick steel plate $10
•  ZX600 Controls $30
•  Hollow Tubing $10
•  Solid rod $10
•  Harley Linkage Ends $25
•  Can of wrinkle-black paint $7
•  Misc hardware (nuts, bolts, etc)   $15
Total $107

Running total for Chopper: $1965