TOPIC:

I've been driving a Z440 LTD for some months now with no mechanical problems. However since a couple of weeks, I have this very subtle rattling noise in my right cilinder which is most apparent when you open or quickly close the throttle. I have difficulties identifying what makes this noise, first thoughts would be spark knock/pinging but maybe it is misfiring or detonation? The sound is the loudest in the right cilinder around the spark plug.

First I thought, maybe its because of a lean mixture. I cleaned the carburetors and changed the rubber inlet manifolds and now the fuel/air mixture seems right according to the brownish color of the spark plugs. However, the noise did not go away.

When checking the ignition timing, the timing seems to be off for some degrees at idle and advance (about the same amount). Could this be the reason for the pinging noise? And how could I adjust the timing, as the coil plate has no slots for adjustments (should I make these)?

That noise sounds like the cam chain or something similar. It doesn't sound like spark knock to me, which typically occurs under high engine load.

Check your valve lash.
Do not adjust your ignition timing.


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A little bit of a late reply as I was working on some other projects in the meantime. But, I checked the valve clearances twice and they were both times within spec.
The sound is very distinct at the right hand side, top engine. So if it would be the camchain the sound should come from the middle right?
Just in case I removed the cam chain tensioner to check it, but it was working properly and within spec.

I also performed a compression test, and the right cilinders compression is low, around 100 psi compared to 145 of the left cilinder, so maybe that's an indication of something. This winter I can work on the engine, but I would rather drive still for 2 months, so If it is something I can fix without an engine teardown, that would be great.

When driving, when I have the throttle stable, there is no noise, but when I open it slightly the rattle comes again, thats why I expected it to be spark knock..
I think I read somewhere that it could also be the primary chain if the chain guides are worn out or broken. Maybe I'll check that next.

It's easy to try some higher octane fuel to eliminate that possibility.

I’ve tried it with the highest octane fuel available, but unfortunately it does not solve the rattling noise.

Timing chain may be loose. Is it correctly adjusted?

The lower compression in one cylinder indicates a problem with rings or valves, but 100 psi should be enough to run until the season is over. Are you seeing any smoke?

Does it have a counter balancer? My Honda 350 didn't have one and it ran great. I hate those things.
Steve

hardrockminer wrote: Timing chain may be loose. Is it correctly adjusted?

The lower compression in one cylinder indicates a problem with rings or valves, but 100 psi should be enough to run until the season is over. Are you seeing any smoke?

It's an automatic adjuster which still looks ok, but maybe the spring is getting a bit weak. I should maybe check it again. And yeah, it runs still fine, even with the low compression, there is no smoke coming from the exhaust. I'm thinking of replacing the valve seals and piston rings, during the winter teardown. But for now its still ok!

SWest wrote: Does it have a counter balancer? My Honda 350 didn't have one and it ran great. I hate those things.
Steve

I think it does have a counter balancer chain, so that could be the problem. But the only way to find out is a complete teardown I guess..

Could be a badly worn piston slapping around.

I would agree with Nessism's opinion that it is not lean knock, or pinging, which would typically appear under load not in neutral revving the engine. Definitely sounds valve train related to me, possibly wear related? You didn't share how many miles on on your bike. It also wouldn't keep me from riding it even though I understand how annoying unexplained noises can be! I'm still getting used to the slides "chattering" on my RS Mikuni carbs. I also don't hear quite as well as I used to according to Mrs. KraZee.

Mike

If the compression is that low, it would be less likely to knock than the cylinder with good compression.

I would put a feeler down the spark plug hole and find TDC and see how much rotation of the crank you can get while the piston is stationary near TDC. Compare that with the other side. That will tell you if there is undo slop in the bearings, wristpin etc.

But the knock could be result of a broken ring causing the piston to rock in the bore under stress. That would also explain the low compression.

Maybe a leakdown test would be in order to see if the pressure escapes through the crankcase, comparing the difference with the good side.