TOPIC:

Greetings KZers,

Since getting my K2 back on the road,  I've noticed how narrow the split between 4th and 5th is.  In some car manual transmissions, I've been able to swap gear sets and increase the split between 4th and 5th to allow for the stock load on the clutch from a stop but lower rpms on the highway.

That said,  is anyone aware of any factory 5th gearsets that are taller than the 1.040 stock sets or any companies that cut custom sets?

Any info would be appreciated. 

Scott

A buddy uses Nove in the UK... but he has pretty deep pockets 

novaracing.co.uk/

My KZ1000 (1980) has a stock gear set.  The 5th gear ratio is 1.22.  How do you arrive at 1.04?

It's in the FSM >> the 81 has different top gears than the 80. 26/25 vs 28/23.

So are the gear sets interchangeable between the earlier motor and the "J"  ?? what is the ratio of the sprockets for both model (final drive ratio) ?

martin_csr wrote:

It's in the FSM >> the 81 has different top gears than the 80. 26/25 vs 28/23.

I don't have any experience with the J engine so I checked and 1.04 is correct!  The difference between 4th (1.175) and 5th (1.04) isn't all that narrow, so I'm not sure what problem results from the low 5th gear ratio.  The J model already has a much higher overall ratio than the A model.  What are the rpm's like at 60 mph?  My Z1 and KZ1000 are around 4,000.

The easy fix for lower highway revs is to change the sprocket ratio, although that will change it in all gears.  

Here in the Midwest US many of the highway speed limits are 75 and 80 miles an hour.

It's not a question of 4000 RPM for 2 hours down the interstate it's more like 6K-7K RPM for 2 hours down the interstate.  That's just a lot of heat and a lot of buzzing going on that makes for an uncomfortable experience.

You are correct,  it would be much easier to change the sprockets, but that increases the load and associated wear on the clutch which i would like to avoid. 

I have the engine out and torn down for other reasons,  so I figure,  now is the perfect time to do a gearset swap of it's possible and not obscenely expensive. 
 

 

The J and GPZ clusters will go in the earlier motors but it's not a straight swap and the Unitrack box is the favorite to use as they are the strongest and factory undercut.
Done it myself a couple of times but there's a bit of machining to the selector drum to clear a gear , one selector fork needs clearancing for another , one gear needs the diameter reducing, a different output bearing and a spacer as well of some shimming to ensure equal spacing of the gears in neutral otherwise it's possible for two gears to become simultaneously engaged at speed which will lock the box and explode the cases at the least.
You also loose the kickstart function due to the different tooth form.

Never known it to be done the other way round as it's a backward step as far as far as mechanical strength goes.

Personally i'd stop over thinking and just change the final drive sprockets to a higher ratio.
It won't bother the clutch..
 

The primary ratio is identical to a KZ1015 engine.  The 5th gear ratio in the J model is lower than in the A model, meaning the combined ratio is favourable of lower rpm at the same speed.  However the chain drive ratio of the J model is 41/15 (2.73) compared to 33/15 (2.2) for the A model.  All of this suggests to me the greatest opportunity to lower revs is in the chain drive.  

I agree if you want to do something, and the different gears exist, now is the time, when the cases are open.  

OkieZ1000 wrote:

It's not a question of 4000 RPM for 2 hours down the interstate it's more like 6K-7K RPM for 2 hours down the interstate.
 

Using ratio numbers for the '81 KZ1000 K1, with a 130 16" rear tire (25.4in diameter), and stock 15/39 chain sprocket ratio, 5th gear at 6k RPM would be 97 mph, and 7k RPM would be 113 mph.  There aren't many places in the US where you can get away with going over 100 mph for 2 hours straight.

Are you sure you're running the stock size chain sprockets and rear tire?

The 900 and 79/80 KZ1000 came with 15/35 sprockets.  Switching to the 35 rear sprocket would put you at 4500 RPM at 81 MPH, and 5000 RPM at 90 MPH. 

Or you could use work your way down from 39 to 35 until you find the right balance.  And you could switch back to stock any time you like. 

DOHC wrote:

OkieZ1000 wrote:

It's not a question of 4000 RPM for 2 hours down the interstate it's more like 6K-7K RPM for 2 hours down the interstate.

 

Using ratio numbers for the '81 KZ1000 K1, with a 130 16" rear tire (25.4in diameter), and stock 15/39 chain sprocket ratio, 5th gear at 6k RPM would be 97 mph, and 7k RPM would be 113 mph.  There aren't many places in the US where you can get away with going over 100 mph for 2 hours straight.

Are you sure you're running the stock size chain sprockets and rear tire?

The 900 and 79/80 KZ1000 came with 15/35 sprockets.  Switching to the 35 rear sprocket would put you at 4500 RPM at 81 MPH, and 5000 RPM at 90 MPH. 

Or you could use work your way down from 39 to 35 until you find the right balance.  And you could switch back to stock any time you like. 

I was thinking the same way.

One minor correction.  The 900's came with 15/35 but the 1015's came with. 15/33.  When rebuilding my KZ1000 I thought they were the same and that's what I have on it.  But it revs much higher on the highway.  I need to buy a smaller rear sprocket to get back to normal.

Just "spit-balling" here as I don't know if it would even fit but the below shows the effect of using a 5th gear set from a Z1300 (0.93) without effecting anything else through 1st to 4th