TOPIC:

So I just bought my first motorcycle, a 1981 KZ550 LTD, for pretty cheap and as I've started familiarizing myself with the bike, I'm starting to grow quite concerned about the sound of the engine on cold start. ( www.youtube.com/shorts/2_fP0PTD488 ). 

There is a knocking that is pretty apparent on cold start at around 750-1500 rpms. The frequency increases as I rev the bike but gets quieter. Once the bike is warm and running its no longer noticeable ( www.youtube.com/shorts/7_wOBYPrlbk ).

Does this sound like bad crank bearings? rod bearings? or something more simple?




 

Post a video of the noise ... my 1980 440 can be quite noisey cold at low rpm ... I do run on fast idle until the idle stabilizes.... I know it is not mechanical ... almost sounds like a mild spark knock....it also is totally quiet at higher rpm and warm
sorry just noticed you did post link to video
that is not what mine sounds like.... hope someone has an answer for you.
I would think it's a rod or crank bearing .... it would me more apparent hot as oil thins

1997dr650 wrote:

Post a video of the noise ... my 1980 440 can be quite noisey cold at low rpm ... I do run on fast idle until the idle stabilizes.... I know it is not mechanical ... almost sounds like a mild spark knock....it also is totally quiet at higher rpm and warm
sorry just noticed you did post link to video
that is not what mine sounds like.... hope someone has an answer for you.
I would think it's a rod or crank bearing .... it would me more apparent hot as oil thins

There are two videos of the noise in question posted already.  Did you not check them out?

Regarding the videos, they sound like primary chain noise to me.  Nothing to worry about.  

Nessism wrote:

1997dr650 wrote:

Post a video of the noise ... my 1980 440 can be quite noisey cold at low rpm ... I do run on fast idle until the idle stabilizes.... I know it is not mechanical ... almost sounds like a mild spark knock....it also is totally quiet at higher rpm and warm
sorry just noticed you did post link to video
that is not what mine sounds like.... hope someone has an answer for you.
I would think it's a rod or crank bearing .... it would me more apparent hot as oil thins

There are two videos of the noise in question posted already.  Did you not check them out?

Regarding the videos, they sound like primary chain noise to me.  Nothing to worry about.