Topic: Knocking solved! Help for others with the same issue.

[Paganica]

Alright so as many of you know I have been dealing with a knocking noise coming from my '76 CB550f.

Well it appears I have found my issue. Unfortunately, It looks like I've got a bad rod bearing on cylinder 4. For anyone else dealing with a similar issue you can test for a bad rod bearing pretty easily using a two part method. If I am wrong about any of this, I hope someone with more wisdom will correct me.

Part 1:
1. Fire up the bike.
2. If the knock occurs at idle, pull a spark plug cap off each cylinder (one at at time) and take note of whether or not the noise disappears with one cylinder in particular. For me, it was cylinder 4.

Part 2:
1. Now that we have determined which cylinder may be a problem, remove the spark plug from that cylinder.
2. Turn crank until the cylinder is just a few degrees past TDC (starting it's way back down).
3. Take a screw driver or some other blunt object and push the top of the cylinder downward. If there is any play at all you likely have a worn rod bearing which totally sucks.

I hope this is helpful for someone else trying to diagnose a similar problem. And as I said before, I hope someone will come along and correct any misinformation. In fact, I wish someone would cause as it stands right now I've got an engine rebuild ahead of me.

[754]

Once you have had one you will know the sound.. If you dont run it too long, crank might be good.
 Remove engine and its sidecovers..split cases. And pull cam out. Can maybe be fixed without pulling topend..

[Powderman]

Usually when trying to determine what the sounds is, as demonstrated in the video,  is followed by very expensive sounding, loud, scary "BANG". . Once you hear a rod knock you learn real quick how expensive it is and hope to never hear that sound again and also refrain from checking the noise again. There's no mistaking a rod knock, listening to it over and over just causes more damage to rod and bearing and eventually to the crankshaft it self.

[Paganica]

Once you have had one you will know the sound.. If you dont run it too long, crank might be good.
 Remove engine and its sidecovers..split cases. And pull cam out. Can maybe be fixed without pulling topend..

Ya I would definitely prefer not having to pull the top end. The bike only has 13k miles but after seeing the burned up tappets I replaced  I am afraid that there will likely be many more issues as it seems the PO ran this bike with either no/low oil or the wrong kind of oil for some time.

its too bad because the bike runs very well and has good compression. I definitely won't be running it anymore. Now I just need to decide whether its worth making the repairs or just finding another motor.

[754]

Let me guess on the seam where the cases meet up........ Is there any silicone squeezed out of there..?

[Paganica]

Maybe a small amount.. It's hard to tell what's behind the crappy paint job but it doesn't look like a whole lot from what I can see. I've seen quite a few top end rebuild forums. Does anyone know of any bottom end rebuild write ups? It seems a bit more complicated.

[754]

That was a  guess, often your cam problems follows something clogging an oil passage ..

[BomberMann650]

oh wow, that was quite a noise

[Don R]

Close to sticking a rod out of the case. W0W! I spun a rod bearing in a Pontiac once, it tossed extruded bearing material clear up into the rocker covers.

[Paganica]

What that little tapping noise? Ahh that's nothing... Probably just need to adjust a tappet or two