After cleaning my wife's F3 chain I noticed that the rear sprocket didn't really fill the chain. We've owned the bike for about 3 months now. I know the chain and sprocket are not original since the chain has a master link with a "clip". The factory chain would have been endless. The question has to do with the fit of the sprocket and chain. In looking at it there seems to be a fair amount of lateral play. I compared it to my 1994 CBR1000F chain (which I replaced 9000 miles ago) and sprocket fit. My chain is an RK chain with AFAM sprockets. The sprocket is clearly wider, about 9.25 mm and fills the opening in the chain. On my wifes F3, the sprocket is only about 7.5 mm thick (at the teeth) and leaves a fair amount of space around the chain. I'm including 3 photos. The first 2 are of the F3 chain and sprocket. The 3rd is of my 1000F.

Should I be concerned that maybe the wrong sprocket was installed when it was replaced ?

 

You're killing me with all the metric numbers -- chains are still measured with old fashioned inches Just from looking at the pictures it appears (I can't be 100% from just a pic) that you have a 525 chain and a 520 sprocket.

Here's how chain sizes work. Of the 3 numbers the first is the center to center distance of the pins in 1/8's of an inch. So a 520, 525, 530 are all 5/8" pin to pin. The last two numbers are the thickness of the sprocket -- only it's in 1/80's. So a 525 chain has a sprocket that's 25/80" thick. A 530 or 630 chain has a 3/8" thick sprocket.

So measure the inside of the chain and the outside of the sprocket -- there should only be a few thousandths difference.

 

Thanks for the information. I've been doing some research on chains, since it's time to replace my wife's F3 chain. I found this information on EK's chain site at www.ekchain.com (she wants a purple one). Looking at the numbers, she's got a 530 chain with a 525 sprocket. I'll be putting both 525 chain and sprockets on it, since that's what came on the bike.

What’s the difference between 520, 525 and 530 chains?
The numbers indicate a chain’s dimensions, tolerances, minimum tensile strength and other specifications, using a system instituted by the Japanese Industrial Standards Committee. The JIS standard is very similar to chain standards developed by ISO, ANSI, DIN and others.
The first digit (4, 5 or 6) denotes a chain’s pitch – the center-to-center distance between chain pins. Originally these numbers specified pitch in eighths of an inch (i.e. a 400-series chain had a pitch of 4/8, or 1/2 inch), but now metric dimensions are used. A 400-series chain has a pitch of 12.7mm. A 500-series chain has a pitch of 15.875mm. A 600-series chain has a pitch of 19.05mm.
The second and third digits indicate the chain’s width, measured between the inboard surfaces of the inner sideplates. An EK chain ending in ‘20’ measures 6.35mm between the plates. If the number ends in ‘25’ or ‘28’, the dimension is 7.94mm. If the number ends in ‘30’ or ‘32’, the width is 9.53mm.
Because wider chains are typically stronger as well, the second and third digits also indicate a chain’s strength, relative to other chains with the same pitch. Higher numbers correspond to greater strength, i.e. a 525 chain is stronger than a 520. This additional strength is achieved through increased roller diameter, pin diameter, pin length and plate thickness.
You should always replace your old chain with one having the same JIS number. Never replace a sealed chain with a non-sealed chain.