Sprocket Life Expectancy

I replaced my rear sprocket and chain on my '79 KZ750 twin a little over a year (and 7,500 miles) ago. This was shortly after purchasing the bike.

The front sprocket looked brand new, whereas the chain and rear sprocket appeared to be original. So I decided to keep the front sprocket, replace the rear sprocket and put a new o-ring chain on.

7,500 miles later and my rear sprocket looks like a Chinese throwing star again. I'm not sure what material the rear sprocket was made out of. It felt light, probably aluminum.

Is this amount of wear normal in 7500 miles? Assuming I replace both sprockets and the chain at the same time am I going to be replacing these parts every 7,000 miles?

Thanks.

If you keep the chain clean, buy a good quality X-ring chain and steel sprockets, you can get as much as 50,000 miles out of a set. A sprocket ruined after only 7500 miles - well, must be close to a record.

faffi wrote: A sprocket ruined after only 7500 miles - well, must be close to a record.

That's what I'm thinking! I'm pretty good about cleaning and lubing the chain, though I admit, I slack occassionally.

I wish I'd kept some info on where I got the sprocket and what it was made of. I'm guessing it must be some soft aluminum.

Given that it's only been 7500 miles, I'm tempted to keep my chain and replace the rear sprocket with a steel one.

For sure something was wrong. Buy Genuine Kawasaki front and rear sprockets and a quality (such as D.I.D.) chain, and hit them with some lube every 3-400 miles. They should easily go 35-40,000 miles or further depending on how hard you ride. Be sure to use a new front sprocket lock washer too. Ed

Aluminum sprockets don't hold up so well, you just kinda forgo them life expectancy for the added perfomance from the weight savings(ive never felt it). I have always heard that you have to replace chains and sprockets as a set, but admittedly I have been known to cheat on that one. I'm sure on day I will throw a chain smack dab in the middle of some ghettto as the clock strikes midnight, but until then I will continue to ride blissfully unaware :lol:

Topper wrote:

faffi wrote: A sprocket ruined after only 7500 miles - well, must be close to a record.

That's what I'm thinking! I'm pretty good about cleaning and lubing the chain, though I admit, I slack occassionally.

I wish I'd kept some info on where I got the sprocket and what it was made of. I'm guessing it must be some soft aluminum.

Given that it's only been 7500 miles, I'm tempted to keep my chain and replace the rear sprocket with a steel one.

The stock rear sprocket is a steel 38T. Z1 sells them for the best price along with steel front sprockets (16T stock, 17T will make your life easier). They also sell really good X ring chain for a good price. Stock chain is 102 link as I recall.

If your sprocket is hosed, it may have screwed up the chain.

Thanks for the help guys. I just counted the teeth on the front sprocket for the first time since buying the bike.

It's got 18 teeth. Everything I've read says you can go up to 17 on the 750 twins, but I haven't heard of anyone going to 18. And it looks like when the chain got a little loose it was tearing the hell out of the chain gaurd that sits in front of the engine sprocket.

So I was running 18 front and 38 rear. I've already ordered a 38T rear sprocket and I'll be ordering a 17T front sprocket. I still need to determine whether or not the chain guard is still usable or if I need that too. And of course a chain.

You may want to go ahead and replace the chain guide if it appears damaged. The really good news is that it (part #12053-1006) is still an active part so it is available from Kawasaki. Ronayers.com lists it at $4.57, so it shouldn't cost very much even if you buy it from a local dealer. Double check the part number. Ed

It's worse than I thought. Cleaned the gunk out and what I took to be a worn chain gaurd was actually the transmission cover. And the clutch push rod has two grooves cut in it from the chain.

The PO must have removed the chain guard to fit the 18T sprocket. And even the slightest amount of extra slack in the chain caused it to rub.



So my guess now is that the chain picked up fragments of my transmission case and used them to grind down the rear sprocket in record time.

That doesn't look good. If you liked the ratio, then you should change the rear also, if you drop 1 tooth in the front. Here is the gear commander tool: www.gearingcommander.com/
You can fool around with it a bit, look at the stock sizes and the ratio, engine RPM @ given speeds. Then make a choice of what you want. Definitely best to replace, all components as a set, sprockets and chain.

Yeah it's breaking my heart (and wallet) to throw out a chain with only 7500 miles on it, but if it's been picking up all that crap, it's clearly toast.

It'll be a couple weeks before I have the time, money and parts to work on this.

Put a magnet on the sprocket if you don't know the material.