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Radically High Gear Ratio on My KZ650 CSR
- WABBMW
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The motorcycle is an '82 KZ650 CSR. The bike uses the big 630 chain. The stock sprockets are 13 front and 33 rear. This gives a 2.54 ratio (33/13). In 5th gear, the bike ran approximately the following RPMs: 40 mph = 3,250; 50 = 4,000; 60 = 4,850; 70 = 5,650; 80 = 6,500.
I discovered that the front sprocket might be increased by only about 1 tooth without hitting the chain guard. The guard is very close to the clutch pushrod, so it cannot be substantially modified. So I looked to the rear sprocket. My engine has a slight harmonic vibration at about 4,400 to 4,700 RPM. This occurred between 54 and 58 mph. I wanted to move this up to around 70 mph. After doing the math, I decided to leave the front sprocket at 13, but change the rear sprocket from the stock 33 tooth to.....(drum roll please)......a 26 tooth. This brings the sprocket ratio down to 2.00 (26/13). The bike now runs the following RPMs: 40 = 2,550; 50 = 3,200; 60 = 3,800; 70 = 4,450; & 80 = 5,100.
Here are the positive results:
The bike has an entirely new personality. At highway speeds, the engine is very quiet, smooth and economical. At 65 mph I have reduced my RPM by over 1,100. Yes, the acceleration in 5th is considerably less, but still very adequate. Besides, what the hey, downshift to 4th or even 3rd and boom - you are rocketing past everything in sight. The gas mileage is now in the high 50s with my best being 64 mpg. As I move up through the gears, the shifting is spread out upwardly. It is easier to shift and coordinate engine speed with bike speed because things happen more slowly. I do not mean that acceleration is slower, but that you are not popping through the gears so rapidly. By keeping the tach in the power band, the acceleration is ever bit as good as before. The difference is that you may be in 2nd gear as opposed to 3rd gear before for a particular speed.
The drawback to this gearing, as I knew it would be, is in starting off in first gear. It is somewhat slow. You have to engage the clutch a little longer than before. But after you are rolling about 5 to 8 mph, from there on up is just music. The bike would not do so well if used to climb a very steep driveway for example. I live in Houston, TX and the roads are quite flat so this gearing suits me well.
I will be glad to answer any questions. I will also do a followup after logging more mileage.
Bill Baker
Houston, Texas
1982 KZ650 CSR
2008 Yamaha FZ1
2006 Yamaha FZ1
1977 Honda Supersport 750 four (sold)
1984 Honda Nighthawk 650 (sold)
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- rstnick
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I added this post to a thread on the 650.ifo/forums site, in a post discussing Gas Milage: MPG
Rob
CANADA
Need a key for your Kawasaki? PM me
1978 KZ650 C2, 130K kms, Delkevic ex, EI, CVK32, PMC easy clutch, ATK fork brace, steering damper, braced swingarm, 18" Z1R front wheel.
2000 ZRX1100
2011 Ninja 250R
2005 z750s
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- JMKZHI
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- CoreyClough
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www.cunnington1.freeserve.co.uk/gearing_v12.xls
Plug in your numbers, and there you go. Change the sprockets on the spreadsheet, before buying new sprockets.
Just remember going too small in the front can cause excessive wear on the chain.
'85 GPz550(ZX550-A2)
GPz550 Base Manual --> tinyurl.com/ze5b3qo
GPz550 Supplement Manual --> tinyurl.com/h34d2o6
GPz550.com --> www.nwsca.com/scripts/gpz_forum_2005/default.asp
First Race Win GPz550 --> tinyurl.com/o5y3ftp
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- apeman
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ALSO: Someone on this board tried putting the SIX SPEED transmission internals from a KZ550 into a KZ650 or KZ750. This would be nice, if it really works. I don't remember how it all turned out. If I get a chance before the weekend is out, I will search for the threads and post a link.
Post edited by: apeman, at: 2007/10/05 14:25
Petaluma and Truckee, CA -- member since Jan. 23, 2003;
PREVIOUS KZs: 1980 KZ750H with 108,000 miles; 1980 KZ750E with 28,000 miles; and KZ750H street/cafe project, all sold a few years back.
This is what I do for fun, not for work. It is art, with a little engineering thrown in.
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- Fossil
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- steell
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ALSO: Someone on this board tried putting the SIX SPEED transmission internals from a KZ550 into a KZ650 or KZ750. This would be nice, if it really works. I don't remember how it all turned out. If I get a chance before the weekend is out, I will search for the threads and post a link.<br><br>Post edited by: apeman, at: 2007/10/05 14:25
The six speed will fit in the 750's (I know for a fact), and should work in the 650's that do not have a kickstart. It's a fairly easy conversion (have to split the cases), but you may have to shim the ends of one or more of the transmission shafts.
Oh great, now there are going to be more people looking for a cheap 550 trans, so I may never find another one
It only gives you just a little bit more on top and bottom, mostly it gives you closer gear ratios, which comes in handy for those with aggressive cams and narrow powerbands.
KD9JUR
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- KZGUY
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- Spot
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Good judgment comes from experience, which usually comes from bad judgment. - Will Rogers
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- Spot
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Good judgment comes from experience, which usually comes from bad judgment. - Will Rogers
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- WABBMW
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Front sprocket: I bought a 16 tooth from Z1. They told me it probably would not fit, and they were right. I was willing to grind, cut, weld, the chain guard, but even if there were no chain guard, and I ground the case supports, it would have hit the clutch pushrod. I was not willing to tamper with this. Your bike must have a different design, or are we talking numbers with a 630 chain? This is a big chain with 3/4" links. So I just left the stock 13 tooth in place. Anybody want to buy my new 16 T sprocket?
Rear Sprocket: I ordered the 26 tooth from Rebel Gears. It bolted right on. Made from aluminum. With the stock sprocket being 33, I dropped 7 teeth. Warning: The stock chain had 84 links. The smaller sprocket needs an 80 link chain. I shortened mine, but I would recommend that "normal" people buy a new one.
My knowledge of the 6 speed transmission is practically nil. I would think that the ratios of the lowest and highest gears need to be spread out somewhat, otherwise all you do is get a close ratio pattern. The perfect set-up would be a 6 speed with first gear low enough to take off briskly, and high gear high enough to cruise at highway speed with low RPM. The sprocket ratios would need to be compatible.
I saw many automotive gear changes made in the mid 1980s. Earlier models would rev perhaps over 3,000 RPM at 70 MPH, but later cars had lower first gear ratios, and an overdrive high gear and higher differential ratios, bringing the RPM down to about 2,000 at 70. I believe that these bikes were designed just before changes of this sort became popular. Of course, motorcycles are designed more for riding pleasure and not to run 200,000 miles without an overhaul. I have had several BMW cars with over 250,000 miles, still ran perfectly and the engines would consume a quart of oil in about 3,000 miles.
Sorry to get so carried away.
Bill Baker
Houston, Texas
1982 KZ650 CSR
2008 Yamaha FZ1
2006 Yamaha FZ1
1977 Honda Supersport 750 four (sold)
1984 Honda Nighthawk 650 (sold)
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- steell
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I've got a KZ440 LTD with a six speed in the back yard. Do you think its tranny will fit in my KZ650 CSR?
The chances are somewhere between zero and none, the 440 is a twin and the 650 is a four, totally different engine design.
If your 650 does not have a kickstarter, then a 550 six speed should fit.
KD9JUR
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