My 73 xlch always had a vibration around 4500 rpm and would disappear at about 5000 rpm.
An old time sportster mechanic told me that I could control that vibration by changing the sprocket gear to a 22 or 23 or 24 tooth, that would change the vibration either up or down, I don't remember. I now have a 21 tooth that came stock with this bike. i bought the bike new so I know it has never been changed. Anybody know anything about this?

Thanks,
Ranjet

 

There is a list of things that will cause vibration such as wheel out of balance, wheel alignment, cracked rear engine mount, loose engine mounts, loose steering head bearings, etc. There are a few more but these come to mind now. Maybe someone else can add to the list.

Start by checking all engine mounting bolts and the steering head nut. Then move to wheel balance and alignment. You can check for cracked rear mount only by removing the engine from the frame.

Regarding changing the sprockets ...
Most guys change the front sprocket to a 23 tooth to reduce engine vibration at hiway speeds. This is not done to correct a problem, but to smooth out the natural engine vibes at those speeds. It does make riding at hiway speeds much more comfortable and i think provides longer engine life. It does also result in less acceleration, which may be most noticeable in 1st gear. But this is minor.

On the 1979-on models a similar result can be achieved by installing a rear sprocket with fewer teeth, like 48 or 49.

More info in this old HotXL magazine article ...
http://sdrv.ms/1kDWecr

 

I 'm putting the rolling frame together now. No bad engine mounts or steering problems. Rims have been trued. I think I'll try the sprocket change when I get to the engine. Still wondering about that swing arm tension. Heading to Vegas today, will stop at the dealer and talk to him.
Thanks
Ranjet