Topic: Cause of vibrations?

[Magua]

I don't own a sohc/4, but your bikes are in the same era as mine so I thought this might be the place to ask.

I ride a 1980 Cb400n and it has some irregular vibrations. They come and go, sometimes the bike will run smoothly, other times it will vibrate when under load or just passing a certain mid point in the rev range.

They started after installing a new chain and sprockets, however this has been determined not to be the cause. They usually go away after an oil change, or are atleast greatly diminished. I have adjusted the chain balancer as of yesterday (will see if it made a diff over the next week or so).

Don't know if there's much else to be said, oh the clutch may be coming towards the end of its life.
I was thinking perhaps a worn bearing, but it's been many thousands of kilometers since this first started (still plausable?)

Any ideas?

[super pasty white guy]

carb sync?

[bryanj]

engine balance chain adjustment

[mystic_1]

You say that if vibrates, but could you describe this a bit more?  There's vibration, then there's shuddering, wobbling, etc.  Any performance change when it's vibrating?  Does it change if you pull in the clutch?  Only happen when accelerating? Different when bike is cold or hot?  When you replaced the chains and sprockets did you change the ratios or chain pitch?

You mention the clutch is worn, is it possible the clutch is chattering?  That is, slipping and grabbing over and over in rapid succession?

mystic_1

[Magua]

engine balance chain adjustment

Adjusted already.

carb sync?

Tried that, but I didn't have enough pressure for the gauges to work very well. Perhaps a leak somewhere in the gauges?

You say that if vibrates, but could you describe this a bit more?  There's vibration, then there's shuddering, wobbling, etc.  Any performance change when it's vibrating?  Does it change if you pull in the clutch?  Only happen when accelerating? Different when bike is cold or hot?  When you replaced the chains and sprockets did you change the ratios or chain pitch?

You mention the clutch is worn, is it possible the clutch is chattering?  That is, slipping and grabbing over and over in rapid succession?

mystic_1

I guess it's more of a shudder usually whilst under load, but not always while under load. No performance change as far as I can see. I'll try clutching in and I'll see what happens. Cold/hot doesn't seem to make a diff. And I don't believe that I changed anything when replacing the chain and sprocket. The clutch still engages, doesn't slip etc, but the biting point as at the very end of the clutch lever and the clutch is nearly at full adjustment.

[Magua]

From what I can remember, clutching in stops any vibrations.

[crazypj]

loose engine bolt, lower rear behind sprocket cover
PJ