Engine rattle

Hi,
I have a 1983 KZ750 LTD w/ 4,000 miles. When I start the bike, (cold) there is a loud rattling noise that comes from the bottom end of the motor. After it is warmed up, the noise goes away. Any ideas as to a fix? Last year I dropped it off at the local MC repair place and they adjusted my valves, which didnt do anything.

Usual cause for that is the primary chain.
Very common.

Steell, Is that possible at only 4,000 miles?

There is no tensioner on that chain, so anytime the cylinder firing is not smooth and consistant that chain will bounce up and down. The reason I think it is probably the primary chain is because it goes away after it is warmed up (idle smoothes out), and the noise from a primary chain is usually described as coming from the left side.
If it was a loose alternator rotor, it would rattle all the time (after it got done chewing up the stator) and would have other symptoms. Loose cam chain noise usually sounds like it coming from the top, bearings knock, pistons knock when cold if clearance is excessive.
After considering the described symptoms, and eliminating all others, Primary chain is all that's left.

Of course it could be something really strange that I have not run across in the last 40 years, I do sometimes learn something new

Post edited by: steell, at: 2006/03/13 20:51

thanks everyone for the replies.
The noise is coming from the left side.
I ordered a factory service manual for the bike, how difficult is it to replace the primary chain? Or do I just tighten it?

You can't tighten it because there is no adjustment, and there is no need to replace it, new one will do the same thing sooner or later, and you have to remove the crankshaft and engine countershaft to replace it (totally dimantle the motor).
If you synchronize the carbs, the noise will probably get a lot quieter or possibly go away. What rpm does the engine idle at when cold? Does the noise go away as soon as you put it in gear?

the carbs were synchronized about 400 miles ago, still the same.The bike idles at 1,100 when warmed up, when cold you have to use the choke or else it will idle very,very low. The noise doesnt go away when you put it in gear, only when the engine is hot and fully warmed up.
I started it today (60 degrees outside), the noise was there but not that loud as compared to a 30 degree day, but it is there and noticeable.
I posted a pic, the noise seems like its coming from the bottom of the motor where it says "kawasaki" on the motor cover.

Looks like the pic didn't make it

If you take a piece of garden/heater hose about 2-3 feet long, place one end against your ear and then put the other end near the motor and move it around, you should be able to narrow the location of the noise to one particular place (cheap stethoscope).
With only 4k miles on the bike, it's difficult to imagine any noise being caused by wear.
If you can pull the clutch in and put it in gear without having any effect on the noise, then that eliminates the clutch release linkage and everything from the clutch on back, including the transmission. If it was the pistons or valves, then the noise would be coming from the top end. The only thing under the round cover on the front left side of the motor is the stator and rotor, and the stator is attached to that cover and don't move, while the rotor is attached to the end of the crank and just spins with the crank, if the rotor was making the noise then it would do it all the time. The only other thing on the left side is the engine countershaft bearing, and it's a ball bearing and don't usually wear out till it has "lots" of miles on it (engine usually wears out first).
That leaves us with the primary chain, or something out of the ordinary that's broken.

How loud is this noise, and does it get louder or quieter when you rev the motor?

The colder the temp is outside and the longer the bike sat, the louder the noise is.
When you rev the motor it actually goes away.
But when the motor is cold, the noise is horrific.
BTW, how do I post pics? It keeps saying I exceed the size limit. Just took pics of the bike today after spending all day cleaning it.

I think maximum size is 640x480 but it might be less.

You do have a 750 four cylinder and not a belt drive 750 twin, right?

steell wrote:

I think maximum size is 640x480 but it might be less.

I ran into having pics too big when I first started posting them, I think its actually 600 though, but you could be right Steell

trying a 640x480. Ok 640x480 works


Post edited by: steell, at: 2006/03/15 03:07