KZ650 Engine knock.

My 1978 KZ650 has just recently aquired a light knocking sound when I let out on the clutch and slowly start moving up until about 2000 rpms. I used a stethiscope to listen to the motor at an idol and as I reved it up and I cannot hear the knock, it is only as I start to pull away from a stop sign or out of the driveway. And it seems like it is at the lower part of the engine. Any help would be great.

is this a constent knock, or could it be from the chain area, years ago I wore a sprocket out, made all kinds of noise, thought the whole bottom end was going to fall out

Check the slack of your chain in the tightest spot. You should have 20~30 mm on the chains lower run half way between the front and back sprockets. If the chain is too tight or too loose, you may get some knocking sounds.

Does your 650 have a hy-vo chain primary drive off the crankshaft. Wear and tear on this chain can cause a knocking (?) noise from bottom end at low rpm. My mechanic said it was just excessive play in chain and "probably" would not be an issue.

The symptoms sound similar to detonation. Are you using quality, high octane fuel? Also, is it possible that your ignition timing is a bit off? Good luck, Ed

650ed, My experience with pinging (detonation) is that it sounds like rattling when you are trying to go up a hill in top gear and lugging the engine slightly. I have NEVER heard pinging when you were getting up to speed off idle.

There are THREE chains on a 650. The primary chain which is a hy-vo chain. Our board has had NUMEROUS noisey 650 threads due to this chain. There is the cam chain. About 90 percent of the cam chains out there in bikes that have never been rebuilt probably have loose or broken parts that the chain rides on. Especially suspect is the front guide which is probably broken. The other big issue is the little rubber fingers that the other guides ride on. There are six of them and they get hard as a rock and cause a lot of noise. The pads on the idler can be hard and you can be hearing noise as the result or the chain very well can be stretched or not tension adjusted properly and can be making the racket.

The last chain is the drive chain which can get noisy if it is slapping on something because of excessive wear or not being adjust properly.

The other "noise" that you could hear are the valves. These can be very noisy if valve clearances are wide. That isn't much of a problem except for the noise.

The last area where there can be a problem I can think of is a totally shot clutch spring rattling. I have seen (well heard) these and they can be annoying but one bad one won't hurt anything. You won't hear the rattle when the bike gets up over a certain speed.

Wow - god I love this forum.

My '78 650 juuuuust started having the same symptom today. Most noticeable at very low speeds - like parking lot riding - and pretty much smooths out above 40mph or above 3500rpm. Tried to make the transmission make all sorts of fun noises by putting it through the ringer up and down the rpm range....shifting fast, hard, slow, up and down....nope. Can't recreate it.

On the ride home....I also went there in my head: Probably the drive chain. Got home, popped it on the stand and found that the rear wheel has a pretty tight spot. Put it this way: the wheel stops itself if I try to spin it hard by hand. I think it only makes a full turn and a half before stopping. Chain has a definite spot that is much looser. 26xxxmi on the clock. I can find out from the guy I bought it from whether it's original or not. I'll check the sprockets too. Good call.

Help me out here, though. The hy-vo primary chain. What the everlasting heck is that?!? And what exactly does it do? Only thought my Sportster had a primary chain.....but sounds like I'm wrong. Would be pretty bummed if that's a problem on my otherwise really pristine and perfectly running Kz650. Love this bike....and want to run it for many years ahead.

The primary chain can make noise at idle if the carbs are out of sync. That's normal.
Steve