The Zephyr Zone

hi on my d2 at 6 k its doing 80 mph ,that's with a 17 front and a 39 rear I'm sure you will notice a change with a 16 tooth ,david

ZR468 wrote:

hugojose wrote:No, unless you are racing (...and you shouldn't be on these old ladies), the slightly slower acceleration will not be noticed. This is a trade off; less revs = Lower acceleration, higher top speed..... Higher reves = Higher acceleration, less top speed.

The RPM will drop about 300. The chain will appreciate the bigger sprocket. I run a 17T. The successor to the Zephyr, and last KZ750 in North America, the ZR-7 came with 16/39 combination, vs the 15/38 of the Zeph, which would drop the revs about 400

Just figured the math of the gear ratios of the front and rear sprockets. It gave me a point of reference to the different RPM drops. From the parts catalog, I see the ZR750 - C2 comes with 15/39 combination and the ZR-7S (2002) comes with 16/38 combo.
Hogojose, do you want to double check your combinations?

I did and you right. I simply had the rears mixed on print, and do have the factory manuals for both bikes. But the facts remains, the newer ZR-7 with same engine had more moderate gearing than the original Zephyr 750. Keeping the 39T at the rear, even the 16T will not drop the revs as much as the ZR-7's, only the 17T will drop the revs below the ZR-7's with 16/38 combo.

Just placed an order for the 16T front sprocket on Ebay. It is coming from UK. The next step is installing it. My calculation is showing a 6.15% drop in RPM at the same speed compared with the OEM 15T. I am looking forward to it.
Btw, was out for a cold ride yesterday, 9C and foggy, but still nice break from the daily routine of driving a car.
Kenny

....and impact gun makes it a lot, a lot, a lot easier.

and a large enough compressor as I found out the hard way...
A regular hobby kind of type will not do

I only have a 24" breaker bar, no impact air gun. It will undo a car tire lug nut. I hope that will work. Do you folks know off hand the size of the sprocket nut? I may need to buy a bigger and deeper socket.
Kenny

It's been so long, but I seem to remember is a 20 mm nut. It's also got a washer bent on the nut, as a lock. You have to unbend this. To undo the nut an electric impact gun would do just nicely...does not need to be air. The sprocket nut is tightened to 72 ft-lb (98 N-M), if it is still factory...by comparison; the engine torque is rated to about 42 ft-lb at the crank...so this nearly doubles it. It is doable with a breaking bar, of course, but is very difficult restraining the bike. The impact gun would take the nut out in about...2 secs, without the need to restrain, or needing extra help... making it a breeze. Make sure you also have a torque wrench.

Put the bike on the center stand, in first gear, and and at the same time have someone stomp as hard as they can on the rear brake. This should be enough to stop the sprocket turning to undo it manually. It's how you have to do it to do it up, so no reason it shouldn't work the other way round.

You can do it all just by yourself when you torque it up by sitting on the bike with the rear brake applied and reaching down to the torque wrench. However for undoing it I reckon you are going to need a second person.

In my case the nut did not come loose whatever I tried.

Even with my son standing on the rear break. A lot of energy is wasted on getting the slack out of the chain and while I could easily rotate the socket wrench (extended with a one meter pipe) for some 45 degrees the nut just didn't get enough momentum. Next I simply blocked the rear wheel with another metal pipe, right through the wheel spokes using some wooden blocks to prevent damage. This helped a lot, not having all that slack I mean, but at the end I was only bending my wrench to the point I didn't dare to go any further. I also heated it up with a torch and gave the nut a good bang with a hammer...



At the end I used my flex to cut 6 sleeves parallel to the nut sides and only then it let go...

it seems to me if the nut has not been touched from the factory or done up to tight ,it wont budge with a bar ,I got a mobile tyre fitter with a big air compressor ,job done david