Replacing Front and Rear Sprockets Question

I am sure this is a silly newbie question but I am still new enough to bikes that I really am unsure of some of this stuff. The drive chain and sprockets are all original so in the near future I plan to replace it, but before that I wanted to do my research and start looking and pricing. Before I can do that though I need to know what to look for and where to start looking. Based on what I could find in the FSM and search the boards via the search function I believe I have a 630 "endless loop" O-ring chain with 84 links. What I am NOT clear on is the stock front sprockets size/tooth count and offset, as well as the rear sprocket size/tooth count? What I could find in the FSM Rear Sprocket size is 218.83-219.33mm with Primary Drive Type: Gear and Chain Reduction Ratio 2.55 (27/22 x 63/29) and Final Drive Type as Chain Drive with Reduction Ration of 2.533 (38/15) 5.652 ratio in Top Gear. Now honestly that really doesn't mean anything to me and not exactly sure what this information is telling me, can anyone enlighten me please?

I am considering changing the front and rear tooth count on my sprockets when I do replace them but I am not sure what I should change the tooth count and where i.e., front or rear or just front or just rear etc.

My riding style is mainly mountains and canyons, highways/interstates, city and small town rural roads so nothing crazy and certainly no tracks, but I would like to give it a bit more zip off the line as long as it is not so much that I sacrifice high speed causing. I have only ridden it a handful of times last fall before the weather gave out and I had to put it up in storage and start wrenching when time allowed. That being said I don't remember exactly what the rpms are at when traveling 80-85mph but I would swear it was at least under or near 5000rpms? I'm running stock tire sizes 110/90-18 and 130/80-18 rear, so if I did change the teeth/gearing what would I expect for revs at 80-85mph after doing so? Would I need to get a different chain size other than the 84 link, and if so then once again what size would I need then?

All of this aspect of motorcycles is completely new and foreign to me so I am very ignorant about what is I am sure very simple and obvious stuff, thanks for bearing with me.

Brett

You should be able to find what the stock gearing should be for the bike and then compare that to what you have, although you say that is original, in which case count the teeth on the sprockets. After that it's just simple maths to work out the effects of sprocket changes. Lets say you had a 15 t front and a 45 tooth rear and the bike ran at 5,000 rpm at 70. If you were to put on a 14t front sprocket and keep the 45t on the rear then your rpm's would be 5,000 x((45/14 )/45/15)) = 5,357 rpm. If you went to a 16t front with the 45t rear, 5,000 x((45/16)/(45/15)) = 4787 rpm

Changing the rear to a 40T would give a similar calculation. 5,000 x ((40/15)/(45/15)) = 4444 rpm

Changing both front and rear, front 14 t rear 50t, 5,000 x ((50/14) /(45/15)) = 5,942 rpm

And so on.

You really need to get a feel for how what you have performs, to know where you'd like to be, whether you want higher gearing for cruising or more acceleration, calculating the rpms at your cruising speed is a good idea when dropping the gearing because you need to know you will still have a reasonable ability to cruise without revving the daylights out of your motor.

Awesome that's exactly the type of explanation I was hoping for, thank you RedHawk!!

Many of the sites I am looking at don't have 40T rear sprockets but 41 is much more common. If mine has a 38T now and I go to a 41T will it be a noticeable "seat of the pants" difference? I'm assuming so but with only changing 3T I'd hope it's not drastically different. As I said I don't want to change the bike completely away from where it was stock, just a little quicker in acceleration response below 50mph, that around town and most roads kinda thing.

Thanks!
Brett

The “endless loop” means that the chain has been riveted together and that in order to get a new endless-loop on you need to take the swing arm off. The old chain you can just as well just grind off.

Taking the swing arm off is probably not a bad idea, as the swing arm bearings and the pivot bolt can need a little bit of CLT and grease, so it don’t rust and get seized.

Unfortunately the air-cooled Gpz750 83-89 (ZX750A1-A5) came with an original 5~6mm offset front sprocket and they were only manufactured in the original 15 tooth configuration.

That sprocket can still be had at JT Sprockets for instance,
www.jtsprockets.com/catalogue/model/1149

Front: JTF514 15 tooth, 630 chain with the 13, 25 filament.
Rear: JTR501 38 tooth.

You can play around with your rear sprocket, but up front you are stuck, if you don’t buy the more exclusive custom made offset sprockets, but I don’t think it’s worth it, unless you are going for a fatter rear wheel.

So your options are to go up at the rear getting higher top speed or go down and gain acceleration.

/A

The GPz 750 is a very quick bike in totally stock form, so if yours is not quick something is wrong. Changing the sprockets from the stock sizes will not compensate for performance problems. If your bike doesn't already have enough "zip" off the line one or more of the following is true:

1. The bike needs a proper tune up.
2. Someone has already changed your sprocket sizes to something inappropriate.
3. Someone has screwed with your bikes engine which has ruined low end performance - such as they put pods on the carbs?
4. You need more experience riding to take full advantage of the quickness of your GPz750.

The stock rear sprocket on the ZX750-A3 has 38 teeth. See:
www.powersportswarehouse.com/p/Kawasaki#...0-A3-1985/080186E-13

The stock front sprocket on the ZX750-A3 has 15 teeth. See:
www.powersportswarehouse.com/p/Kawasaki#...0-A3-1985/080186B-13

That sucks. If you can only get a 15 tooth front sprocket, then you will have to play with the rear. I have 16 up front and 35 on the rear. If I want to be quicker off the line I can put on my 15 tooth but then I'll be at 5000 RPM at 70. I like the way it is now, 4000 +/- at 70. Yeah I have to drop down a couple gears to get into my power range but I do more HWY riding than stop and go. :whistle:
Steve

Mine has 16/42 stock and a 15 T front will defently make it snappier but on the highway it is a little much (approx 400-450 rs more) and always ended up going back...... the 41 T rear you talk about will do "about the same"..... since you cruise at 80-85 it might be a little much...... but would be fun hammering on it ........ maybe try to use redhawks formula to figure out just how much of a increase it would be.

For most bikes running a 630 chain the general recommendation is to switch out to a 530, but that offset front sprocket puts you in a bind. I'd do the stock 15/38. You can go to more teeth in the rear if you want more acceleration, but the tradeoff will be more rpm's on the highway. Typically three teeth in the rear is about the max unless you want to work on your wheelstands.

Edit: you might want to search around for some 530 conversion sprockets. Question is whether or not anyone makes an offset sprocket for the front. The rear should be easy. Since the stock 630 sprocket is a 15 you would want to move to a 17 or maybe an 18 in 530 otherwise you will lose too much diameter. The match for the 17 front would be a 43 rear in 530.

+1 With stock sprockets the GPz750 ran the 1/4 mile in a mere 12.4 seconds and has a top speed of 136 mph (see link below for specs). That should provide enough "zip" on the street for anyone and is very quick and fast for a 30+ year old bike. If the owner plans to race on the street against modern 10 second 1/4 mile sportbikes I believe he will be disappointed unless he makes radical, expensive changes to the engine. I suspect the bike in question is not running up to the full stock performance level or that the rider's lack of experience is hindering the bike's performance; otherwise it is very unlikely he would be looking for more "zip" off the line. My recommendation is to first get the bike running up to stock specs and then see if any changes are still desired. Ed

www.motorcyclespecs.co.za/model/kawasaki...aki_gpz750f%2083.htm

My experience with most of the Kawasakis I've owned or ridden is that they are usually geared fairly low and sporty in their stock configuration and you often find yourself looking to upshift when you are already in top gear. I see some people running some very low gearing but usually I find myself contemplating going the other way for a more relaxing cruising speed. If you lower the gearing this really only has a big effect on your first gear and initial get away since once up and rolling the bikes will rev through the other gears quickly enough for all practical road going purposes.

redhawk4 wrote: My experience with most of the Kawasakis I've owned or ridden is that they are usually geared fairly low and sporty in their stock configuration and you often find yourself looking to upshift when you are already in top gear. I see some people running some very low gearing but usually I find myself contemplating going the other way for a more relaxing cruising speed. If you lower the gearing this really only has a big effect on your first gear and initial get away since once up and rolling the bikes will rev through the other gears quickly enough for all practical road going purposes.

Got that right!! I'm always looking for that elusive 6th gear!
I had a 14 and 35 on the KZ1000A1 for a while last spring and summer....and it was wicked fast up to about +110mph-115mph.... then I put a 15 tooth on it to lower the RPMs on the freeway....and it is still wicked fast!!!
But it is more calm on the freeway and I actually considered trading off a little of that wicked fast crap for a more sedate cruising RPM.
So I did what Steve did, and bought myself a new 630, two link longer chain, a new 35 tooth rear and a 16 tooth CS sprocket that I will be trying this season. I could put the new 33 tooth rear on too but that be neutering it a bit too much.
I suspect it will still pull like a freight train....

I have a 92 link chain, 16/35. When I finally get my longer arm on, I will order a 104 chain. A 15/33 combo sounds interesting. Kinda like splitting the difference.
Steve