Shaft drive

[Gene]

 From what I understand, most if not all 83-85 4-cylinder Nighthawks have shaft drive. I have a 85 650sc NH, and after reading several period magazine reviews, it should exhibit some jacking of the swingarm. I haven't noticed any.

Happy Holidays/Christmas to those it applies to.

[Bob H]

...jacking of the swingarm, I haven't noticed any.

Some shaft drives are worse than others.
I had a 1982 Yamaha Seca 750 with a shaft that would lift the rear of the bike when accelerate, then fall when let off throttle. Otherwise it was a great bike.

... after reading several period magazine reviews, it should exhibit some jacking of the swingarm,

The Magazine writers have to think of something to say. I have seen some pretty odd articles over the years.

[Pete in PA]

A longer shaft produces less jacking. The shaft is very long on the 650 NH.😁🤷

[mollusc]

Not all were shaft, but the North American ones were.  The Horizon (CBX 750) is chain drive.

[Pete in PA]

"I was good this year and still got the shaft!"

[Larry Fine]

The first 550SC and 650SC Nighthawks were SOHC, 5-speeds, and chain drive.

The DOHC engines had 6-speeds and shaft drive, except for the '72-73 750SC.

By the way, in case you were wondering, the SC stood for Sport Custom.

[mollusc]

The SOHC bikes were all before 1983.

Getting back to the original topic, I also never really noticed any jacking from the driveshaft on my 700S.

[timberwolfe]

How would you recognize jacking? I never felt anything unusual on my NH.

[Larry Fine]

How would you recognize jacking?

You would feel the seat rise slightly when you accelerate hard.

It's caused by the pinion gear trying to raise the swing-arm pivot upward in its attempt to push the front of the ring gear downward.

It's  the same force that makes the front of the differential rise in a car.

[timberwolfe]

OK, I believe in jacking, but it's messing with my brain. Next time I ride, I'll accelerate hard and see if I can tell anything.

[Larry Fine]

It's caused by the pinion gear trying to raise the swing-arm pivot upward in its attempt to push the front of the ring gear downward.

Maybe it would be more accurate to say that it's caused by the swing-arm pivot resisting the rise caused by the pinion gear trying to walk up the ring gear.