Topic: Rotor swap

[Don R]

 Since I have the dyno cover off my 836 to degree the cam, and there is a partial F2 motor on the floor does it make sense to swap the rotors? I read the F3 rotor is lighter. A guy I know snapped one off at the crank. He thought I should lighten it.

[scottly]

From what I've read, there were two rotors; the early ones had a flange, and weighed over a half pound more the the later style. I don't know when the change was made, or if the F3 was lighter than any previous rotor. If I recall correctly, a K7 rotor weighs about 4 1/2 pounds, while a K1 rotor was about 5 1/8 pounds. I can get you an accurate weight on the K7 rotor, down to the gram, if you like; I have it written down somewhere..

[754]

Run the lighter looking one if you have two different..

 Unless you are in a drill team,  run two up mostly with lots of. Baggage , or pull a trailer

[Dream750]

I “borrowed” this pic from Cycle X when I did my K1/811 build – note the weight differences:

[scottly]

Those weights must include the starter clutch assembly? My weights were without the clutch. My cut-down K1 rotor ended up at 4 pounds.

[scottly]

Found my notes: stock K7 rotor = 2079g (no clutch).

[Dream750]

Those weights must include the starter clutch assembly? My weights were without the clutch. My cut-down K1 rotor ended up at 4 pounds.

Yes, with the starter clutch. I never ran a cut down rotor, how do you like your 4 pounder? 

[scottly]

The cut down rotor works fine, but I didn't notice as much difference as when I first swapped from the K1 rotor to the K7 rotor. I've also remembered a member's previous post that stated the early rotor was 1.234 pounds heavier, and how it was an easy number to remember. That jives with the cycle-x numbers.

[scottly]

Here is a pic of my cut-down rotor along with a K7 rotor:

[Don R]

I checked with a caliper, the F2 looks the same to me as the K4. Thickness and width wise. Hmm. I just read the black motors had a lighter rotor, maybe not.

[Don R]

Thanks for the picture.

[Dream750]

The cut down rotor works fine, but I didn't notice as much difference as when I first swapped from the K1 rotor to the K7 rotor. I've also remembered a member's previous post that stated the early rotor was 1.234 pounds heavier, and how it was an easy number to remember. That jives with the cycle-x numbers.

Thanks Scott. I was too cheap to have my K1 rotor lightened and went with the stock late style - year unknown. Been wondering about that decision ever since. 

[scottly]

A prudent decision on your part, IMHO. I had a lathe and the time and the K1 rotor, so I thought what the heck? If I screwed it up, oh well, I still had the K7 rotor. I'm still curious just when the rotors changed?

[754]

Heavy ended in 72
 I like the lightened rotor, really handy when slipping clutch off the line if you start to bog, easier to control rpm and recover.
 In traffic if i am at the bottom of second gear, i do not always down shift, just as easy to use the clutch and slip it, save shifting twice.. You need a strong clutch..