Topic: Comparing Honda 750 Rotor to Light Weight RC Engineering Rotor

[Jerry Rxman Griffin aka MuthaF'er]

There's been some discussion here lately about light weight alternator rotors so I thought I'd do some digging and get the factual information.

Comparing a stock late model rotor to a RC Engineering light weight rotor you can easily tell the difference. This stock rotor with the starter clutch intact weighs in at 5lb 12oz while the RC rotor without starter clutch weighs in at 3lb 6oz. I first thought the RC rotor might have actually been from a smaller bike ie 350/400 but I did not have those to compare to. It could perhaps be but it can be turned down from a stock 750 rotor as witnessed by the comparative pictures. You'll also notice what appears to be a spacer to make up for the shorter width of the RC rotor.

[voxonda]

Hey Jerry,

Think the spacer is not to compensate for the smaller width, but to 'plug-off' the oilchannel in the crank. This channel provides oil to the starterclutch.

This is my rotor.

Oil channel

My spacer is a innerring from a ballbearing.

Cheers, Rob

[754]

You shortened the crank, & used a 400 rotor? Did you change the taper  depth in the 400 rotor?

[voxonda]

Hey 754,

This is a 750 rotor that I lightened, nothing done to the crank.

Rob

[lordmoonpie]

I shortened the crank reduced the taper and used a CB350 K4 twin rotor....even lighter! 

[scottly]

Hey Jerry,

Think the spacer is not to compensate for the smaller width, but to 'plug-off' the oilchannel in the crank. This channel provides oil to the starterclutch.

My spacer is a innerring from a ballbearing.

Cheers, Rob

Rob, if the job of the "spacer" is to block the oil jet in the crank, wouldn't an aluminum sleeve be lighter than the bearing race you are using?

[voxonda]

Hey Jerry,

Think the spacer is not to compensate for the smaller width, but to 'plug-off' the oilchannel in the crank. This channel provides oil to the starterclutch.

My spacer is a innerring from a ballbearing.

Cheers, Rob

Rob, if the job of the "spacer" is to block the oil jet in the crank, wouldn't an aluminum sleeve be lighter than the bearing race you are using?

Hey scottly,

Absolutely! But this was 'on hand'. Maybe in a later stage will switch to a alu sleeve.

Rob

[754]

1/6 of the weight, cause it would be thinner.
 Moving the rotor inward, increases lean angle, and may reduce crash damage..

[Big Jay]

When we lightened the factory light rotors, people started having dead battery issues.  That was about the time the bikes came out with "always on" headlight.

Jay

[MRieck]

 That thing is gutted. The later ones were 2.161 or something. That thin thing is BS.
  Mike

[Jerry Rxman Griffin aka MuthaF'er]

When we lightened the factory light rotors, people started having dead battery issues.  That was about the time the bikes came out with "always on" headlight.

Jay

Jay,

How did your's compare in size, weight, and shape to this RC Eng rotor?

[Ricky_Racer]

That thing is gutted. The later ones were 2.161 or something. That thin thing is BS.
  Mike

'splain, please!  RR

[Retro Rocket]

There is a guy on here that mated up a VFR 800 { i think} rotor to the Honda crank to give him more charging power for his fuel injection set up, all i know is that it was heaps lighter and produced a lot more power than the standard rotor and if i remember correctly, it was then possible to remove 18mm from the alternator cover. The guy that did it  put a spacer on the crank to make it sit in the correct position for the stock cover.

Mick