6-speed Transmission Swap Instructions

Saablord wrote: I thought about doing this when i swapped a 650 into my 550 (it blew a rod) but eh i didn't feel like splitting the case.... I calculated the ratios and I get 5.8mph more (62.7mph) at 4500rpm in 5th with the 650 over the 550 in 6th so thats nice.

I am curious though, can the case be split and the 6 speed installed without removing the crank/pistons/head etc? I can't remember how that part went when i took apart the 550 motor.

The engine cases can be split without removing the cylinder head, pistons or crank. Just turn the entire engine upside down and remove the lower case to access the transmission. BUT...the clutch, oil pump and secondary shaft have to be removed first in order to fully split the cases. A full read through in a service manual will explain that in more detail.

Tyrell Corp - I think you are correct about the torque on the transmission being a possible reason that Kawasaki never put a 6 speed in a 750. The 5 and 6 speeds share the same bearings, so there had to be a load/shear failure formula of some kind that was used to determine that the reliability of the transmission as a whole might suffer.
But I have read of guys putting these into gpz750 race bikes and they never mentioned one exploding. Drag racing with one is probably a bad idea considering material that I removed from the clutch hub, but on the street I have zero concerns that the transmission will grenade itself.

Slightly less bulletproof is still bulletproof isn't it?

Thinking more, they managed to beef up the zx750 turbo transmission from the z650 parts bin , so I suspect it was maybe more of a marketing/build cost decision.

Also the competitor's GSX750 and Honda CBX750 were 5 speed too, so not really expected at the time in that market sector.

Finally, the original 6 speed z500 /4 was the most modern and last incarnation of the aircooled 8 valve fours , the latest design -
the GPz750R1 in comparison more 'mutton dressed as lamb' as in the last rendition of an older z650 design.

Kawasaki had the '82 62 hp GPz550 unitrack ready for 1981, but wanted to keep something back for the next model , again marketing above engineering.

So they could have, and probably should have, but didn't for exactly the right reasons that seems so wrong to us.

**I noticed that the attachments for the transmission fork orientation in part 2 have since disappeared for some reason. So here are the missing pictures with the instructions**


The transmission is simply installed in place just like the 750 transmission, only making sure that you have the correct style bearing cap installed for your particular clutch release type.







The 550 shift drum installs in exactly the same way as the original, BUT TAKE NOTE OF THE ORIENTATION OF THE SHIFT FORKS!
On the 550 models, the longer side of the fork boss faces the RIGHT-hand side of the shift drum.
On the 750 models, the longer side of the fork boss faces the left-hand side of the shift drum. THIS IS WRONG!

CORRECT!





WRONG!

Just checking in to note that I have put 2500 miles on my transmission conversion illustrated here, and have nothing to report other than it still shifts and operates exactly as intended.
I still cannot imagine riding this bike without the added highway gear.

That is all for now.

I did the 6 speed conversion about 7 years ago on my Z650 B1. I already had the 810 overbore. Now I have a draw through turbo with lower compression and the 1981 kz550 6 speed still works fine without any issues. I also replaced all the trans bearings during the engine re-build last year.

stone fruit wrote: I did the 6 speed conversion about 7 years ago on my Z650 B1. I already had the 810 overbore. Now I have a draw through turbo with lower compression and the 1981 kz550 6 speed still works fine without any issues. I also replaced all the trans bearings during the engine re-build last year.

In the interest of sharing knowledge, how did you deal with the clutch nut not fully screwing on? Do you run yours with the nut a couple of threads short or did you machine the nut or hub? I’m curious how the different methods of dealing with this issue hold up to real world use.

In the interest of sharing knowledge, how did you deal with the clutch nut not fully screwing on? Do you run yours with the nut a couple of threads short or did you machine the nut or hub? I’m curious how the different methods of dealing with this issue hold up to real world use.

I left out the thrust washer and used thread lock on the nut. I’ve also recently installed an MTC multi-stage lock-up with Ballistic friction plates, Barnett cryodised aluminium drive plates and 750 Zephyr springs. Also 750 Zephyr basket and a nos Kz650 hub and the whole setup works great.

I going to do the mod on my zephyr 750, and have bought a gearbox from a zephyr 550, but i´m not sure if I should make the collar mod you did - or not?
or can I use a spacer ?

Brewmaster,
Because the zr550 output shaft is almost 10mm longer than the kz750 output, you are going to need to determine your chain alignment before you know if that collar needs to be trimmed down. I had to cut my collar down because the offset sprocket I had to use wouldn’t fit on the shaft until the collar was cut down. You may have no such issue. But, unless you are running a wider rear wheel or swingarm, I have a feeling your front sprocket is going to stick out farther than your rear sprocket. you “may” end up needing an offset sprocket turned backwards to make it properly line up with the rear sprocket, and then the collar may be in the way. But if you are putting in a wider rear wheel/swingarm then I feel you will have zero reason to modify the collar.
So....just bolt your bottom engine case back in the bike (with the transmission of course) and determine your chain alignment first before you go any farther. If you find you need an offset sprocket for the front, buy it and make sure it bolts up on the output shaft before you bolt the engine back together. As if you do need to cut down the collar, it isn’t easy to remove from the shaft while it’s on a workbench, and it will be harder when it’s in the bike.

I hope this helps!

the shaft from the zephyr 750 is longer than the zr550.
the 750 collar is 33,06 mm + the half of the sprocket = 40,06 to the middle of the sprocket
the 550 is 42,8mm to the edge - If I go for a flat sprocke, it´s minus 3,5mm = 39,9mm to the middle of the sprocket
(I hope you undestand?)

You are correct! The Zephyr 750 output shaft is ~14mm longer due to having a much wider swingarm and rear wheel setup than the kz's did. ( My brain keeps reverting to kz parts instead of Zephyr parts) Side note: The zr-7 output shaft is even ~3mm longer than the Zephyr 750.

But your your photos are a tad confusing as the readout on your caliper measurements are all in negative, so I'm not sure if you are showing a difference in overall measurement or what. For example I know the shaft collar on the Zephyr 750 is supposed to be 37mm not 33mm. Since I'm not following along with your math, I can't confirm what offset sprocket size you need. Once again, you need to bolt the engine case in the bike and confirm chain alignment, because if your math is off by more than a couple of millimeters, your chain is going to eat sprockets.
But to answer your initial question, I can almost 100% guarantee you won't need to modify the shaft collar at all.



But webike.net did have a plethora of offset sprockets for Kawasaki's and Suzuki's which use the same splines as Kawasaki. And at least some Sunstar sprockets come pre-drilled for the 550 sprocket retainer bolts.
img-webike-370429.c.cdn77.org/catalogue/...ont_spk_images-3.jpg