Topic: CB650 "knocking"?

[mgbgt89]

I've got an 82 nighthawk 650, that i fear may have some serious damage.

I was riding it to work last week, merging onto the interstate. Suddenly, it cut out and died on me. Restarted it while still in motion, let out the clutch and it was WAY down on power, and had a knocking noise above 5K rpm. Not a serious knock like i've heard any other engine make, i'm not sure if i would even call it a knock. When i got off at a ramp, smoke was rolling from the engine breather.

I took it home, drained the oil expecting to see big chunks of aluminum. Nothing. Checked the valves, they were a little wide, so i set them. Tightened the cam chain while i was at it.

Still having this knocking noise. Its way down on power. Idling or puttering, it runs fine, no noise. If its under load and reaches 4500-5000 rpm i can hear a noise that shouldn't be there.

I've had issues blowing out exhaust gaskets since the #$%*ty mac collars bend instead of smashing the gasket all the way. It could possibly be one starting to let go, but i can't feel any exhaust coming out around them. I know what that noise sounds like, and doesn't quite sound like that.

I looked at 2 of the plugs, both were slightly lean, but still had some brown color. Not as rich as i would like it to be, but i don't think lean enough to cause damage. I would think a holed piston would cause it to smoke very badly, and make a ton more noise than this is making.

Any idea what this could be?

[mgbgt89]

I recently pulled it out of long term storage about a month ago, since my 350F is down for a re-gasket. Been riding it every day since. Carbs were empty and tank full. Fresh gas and battery and it fired right up without issue. Not sure if that makes a difference or not.

[mgbgt89]

I'm leaning toward big end bearing. Looks like my riding season is done early. 

[Danno]

you could have stamped a valve do a compression check to find out otherwise it could be a big end bearing but knocking above 5krpm sounds more like a stamped sticking valve you can also get one of those snake cameras like they sell in the tek 4 line at home depot and pull the plugs and look in the bore at the top of the cylinder you will see the valve stamps if that is what happened

[mgbgt89]

As in floated one and bent it? Possibility. I can't remember what RPM i was running when it happened, but i'd imagine it was up there pretty high since i was trying to merge.

I'll see if i can borrow a compression tester and check it out. It definitely feels like its missing a cylinder. Fixing a valve would be a hell of a lot easier than putting in a new crank.

[mgbgt89]

Would that make noise only under load though? As soon as i lift the noise goes away, regardless of RPM.

[Danno]

it would make the noise at higher rpm like say 5000 if you are having noise under load is it still above 5000 rpm or at low rpm?
the lower the rpm the more likely a bearing but I am still leaning toward the valve stamping because unless you have a plugged oil screen or some other reason it is not getting oil it is unlikely  but you can drain the oil and drop the pan and find out just by looking in the pan for shards of metal  while you are in there check out the primary chain and make sure it is not hitting the case also I can't remember what type of cam chain tensioner it uses look for pieces or plastic or rubber in the pan the pan has an O ring and as long as you don't damage it you can put it back on when you are done looking

[Danno]

I don't know what you mean by lift? is it knocking at idle ? if it is a sharp knock like a hammer blow it could be a main bearing but if it is a dull knock then it could be a primary chain the 650 has an even better oil system then the 550 it has extra gear oil feeds and runs high pressure like the 550

pull the pan bud this is starting to not make sense

[mgbgt89]

Noise only happens above 5000 rpm or so. If i lift off the throttle when it starts to make noise, it stops. The noise only occurs under load, and at mid to high RPM. It's a dull knock, not sharp like say piston slap.

The noise happened all the sudden, I've only ridden it about 4 miles after changing the oil to see if it would go away with fresh oil. It didn't. I'll pull the pan and see if anything bad is waiting in there, but the oil i drained look clean, didn't see any metal in it.

[trueblue]

if the noise goes away when your off power and it only does it at higher rpm it sounds like a typical big end bearing knock, it usually sounds heavy and dull, like something is about to part company in a big way.

[KingCustomCycles.com]

The noise goes away as the rod "floats" away from the journal as the force is relieved and oil rushes in to fill the large gap.  It returns as the rod is once again loaded and breaks through the oil.  You may, or may not, find chunks of the bearing in the oil pan.