So here is some more of the build of Purple Passion. I am switching to mag rims so I bought a rear wheel from a 1983 GS550L. I plan to mount that but in the short term I grabbed the rear wheel off my 1983 GR650 Tempter project (future) bike and dropped that on since it had a tire on it. The rims have different OEM PN's but both will work as a straight drop in replacement. I am running the stock crush drive and stock brake hub.
From there I set out to do the chain conversion. Now I am running a 130/90-16 rear tire so that increases the rear tire diameter from a stock 23.8 inches to 25.2 inches which is about a 5.9% increase in final gearing (or reduction in rpms which ever way you want to look at it). My target was about a 10% increase in overall gearing and I wanted to keep the front sprocket as relatively large as possible to limit the load on the counter shaft bearing. For the sprockets I chose a 17/49 combination 2.6% taller gearing than stock pulleys. However that combined with the bigger wheel diameter then gives a total overall gearing increase of 9.5%. This takes my speed at 4,000 rpm from 59 mph to 65 mph or look at it the other way if you prefer at 60 mph my revs drop from 4,050 to 3,700 rpm. Lastly if my wife ever wants more acceleration and get back closer to stock then I can drop the front sprocket one tooth to a 16 tooth and I am at only 3% over stock.
If anyone is interested in looking at a chain conversion I have a nice Excel spreadsheet that looks at all the ratios and speeds by 100 rpm increments. All you punch in is your tire diameter and front and rear sprocket or pulley sizes. Just send me an email and I will shoot it too you.
It looks something like this.
I went with EK530RX X-ring chain with steel JT sprockets.
Now I did find with that sprocket combination I was running ended up very close to the end of the axle slot. Once the chain were to stretch and wear the sprockets a bit I would run out of adjustment and then have to take out another two links. This also would negate my ability to drop the front sprocket by one tooth quickly. So I decided to slightly lengthen the slot forward in the swingarm. I clamped it up in the mill and ended up lengthening it by about 0.230". Here is a picture of the stock slot compared to the lengthened slot.
This allowed me to shorten the chain by 2 links and run closer to the front of the slot. Of course it is never quite that easy. I found that my chain adjusters were just a hair too short to get that full 0.230" so I went to my favorite hardware store...Ebay! I bought a set of GS450 chain adjusters and it was off to the races! Here are the adjusters side by side S-40 and GS450.
Here is a picture with the chain adjusters on.
Ok so now that the driveline was sorted out I wanted to retain the stock belt guard. This is what it looks like stock with a 49 tooth rear sprocket. I really didn't like all the daylight between the guard and the sprocket & chain.
Just to keep the pictures close here is where I got too.
To get there it required a few small modifications.
First I forgot to mention that I cut off and ground away the vertical mounting tab that is on the swingarm as well as the inside of the belt guard. This was to allow clearance for the chain. Next I had to trim off part of the bottom of the guard or it would hit the SA when I dropped the back.
Here is what it looks like trimmed and in place. I also had to trim just a little up where it wraps over the front of the SA by the front screw.
The last thing I had to do was move the mount hole on the rear tab of the guard. I pulled the shock bolt out and dropped the guard down in place and marked the hole. Here it is drilled out.
and then slotted
I realized I never took a picture at the very end so you will have to use your imagination but I cut the two little odd tails off so it looked more like the stock shape.
Over all I am very happy with that part of the conversion.
I just installed my Verslavy and next I have to fix the head plug leak and set the valve adjustment.
After that I will move on to the new front mag rim and a 320mm rotor and caliper upgrade for that wheel.
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