This is a summary of the 6-speed transmission swap I did on my 81 kz750e. Because I could not find any instructions to do this modification, I researched the subject for months. These are the final results of my efforts and are not the definitive instructions, but simply the way I went about it.
** These steps are for informational and purposes only, and I am not responsible for any injuries, damages or mistakes you incur if you decide to follow these steps!**
**If you do attempt this conversion, follow any related disassembly and assembly directions and torque specs in your specific service manual for your specific bike.**
**It is possible to use these instruction to swap a 6-speed into any four cylinder kz750 model, Zephyr zr750 and possibly a zr-7. This can also be done on a kz650 but the kick start mechanism will have to be deleted and a later style non-kick kz650 clutch cover used. **
To preface this, my entire goal of this transmission swap was to be able to keep the stock gearing on 1st through 5th gear, and yet add a usable overdrive to keep revs down while on the interstate. So when I was researching this swap I got on gearingcommander.com and started running all the numbers to see if what kind of RPM’s and speed benefits could be made by using the 550 6-speed transmission.
This is the factory kz750e gearing stats:
This is what I used for my particular build.
(Your results will vary depending on your rear wheel and tire sizes.)
1. 6- speed transmission from a 84 zx550
2. 530 pitch chain
3. 750 clutch with 2.55 primary ratio
4. 17 tooth front sprocket with 13mm offset
5. 39 tooth rear sprocket
6. 140/70-18 rear tire and rim from a zr550
For a final result of:
What is needed to be sourced for the swap:
1. kz/zx/gpz550 (They all have the same gear ratios. I had two ’84 gpz550 transmissions in my basement so that is the only reason I used that particular model.)
**The Zephyr zr550 and 1985-1997 zx600a/b/c 6-speed transmissions have a ~10mm longer output shaft than the kz/gpz550’s. Thus requiring a smaller offset sprocket which is very important when doing this swap on a Zephyr zr750 or zr-7. Those bikes have longer output shafts to accommodate wider swingarms, rims and tires.**
2. Shift drum and selector forks and rod from the corresponding 6-speed transmission.
3. zr-7 shift return spring. This can also be found in zr550/750’s, zx600’s and other bikes (part # 92144-1074)
4. 550 front sprocket with mounting holes tapped in it.
Your particular wheel and tire size and chain pitch will dictate how many teeth and what offset the sprocket will need.
5. Front sprocket splined keeper plate and bolts. Part # 13270-1060
6. Rear sprocket and corresponding pitch chain. (530 pitch preferably due to availability of offset sprocket choices. Also order a 120+ link chain and cut it to length.)
7. Heavy duty or hardened washer with 20mm ID (optional)
6-speed bits
Picture shows a spacer that came with the sprocket but was not needed.
What will also be needed but can be reused from the original 650/750 engine:
1. Transmission bearing cap with clutch pushrod port/guide. ( The gpz transmission I used was not a pushrod clutch, so the bearing cap was the wrong style. If you are doing this on a later model 750 with the lever pull-type clutch release mechanism, then this not needed.)
2. Gear selector linkage.
3. Transmission cover
4. Clutch assembly
5. Neutral spring and plunger
6. Shift drum alignment bolt