Topic: CB550K weird noise at idle

[Geoff Hastings]

Mine made that rattle when the clutch centre nut came loose, it does sound on the video like it’s not idling on all four cylinders though which won’t cause the rattle but the rattle does show the uneven tick over.

[M 750K6]

Tickover is too low. Tachometers are not accurate. My 750 rattles a lot like that at 950rpm. It is smooth at 1400rpm. My 4cyl Suzuki Bandit ticks over smooth at 1100rpm. Listening side by side, I would struggle to believe the Honda is revving higher than the Suzuki. So, I reached the view the tachos are indicative, not accurate meters.

[Deltarider]

That's also my experience. I once worked on a K3 that didn't tickover at 1000-1100 checked on a true tacho before the onboard ND tacho showed 1400 rpm. If you then, with such an inaccurate tacho would try to set the idle at 1000-1100, by looking at that onboard tachometer, it won't work. The rpm in the video is definitely too low and I find it amazing that when you hear those sounds the engine didn't quit, because at that particular point, the rpm is definitely too low. Hence my advice to first verify the rpm with a known good tachometer. Then the rest of the usual suspects.

[dave500]

never let a cold carby engine idle,keep em at a fast idle untill warm enough to ride away,younger guys with only injected car or bike experience expect them to idle clean straight after start up?

[Deltarider]

never let a cold carby engine idle,keep em at a fast idle untill warm enough to ride away,younger guys with only injected car or bike experience expect them to idle clean straight after start up?

Right, old boy! Too many expect to behave their bikes like the cars they own. K3's in particular have a funny cold start behaviour. When you pull the choke and press the starter button, they usually race to 4000 immediately. It's a consequence of the fast cam which was needed, since Honda had been forced to lean the carburetion ('77 models). As a matter of fact, the K3s (and K4s) are the only in the CB500/550 series where you need the choke partially pulled in the first km or so. That's why the knob is on the handlebars in your view. Previous models with the old style carbs behaved differently and you could reopen the chokes fully before departure.

[galoebi]

Here is the video with the engine warmed up:

I am now pretty sure that at least a part of the sound comes from the clutch basket. Does anyone know where I can get the replacement rubbers? I could not find any.

[Oddjob]

Do you know what’s involved in changing the basket rubbers? It’s not a job for someone without a good amount of experience with these engines. The only source I know of is in Europe and they refuse to post outside of Europe. Won’t even post to the UK.

[Deltarider]

I'm not convinced yet. Here is what I'd do. Have the engine idle when it's really dark. Closely watch the plugcaps and their HT wires and make sure there is no intermittent arcing to the head. Also I'd like to see a similar video like you did, but then concentrate on the ignition plate after you've removed its cover. I'd like to see the points in action and see if there's any intermittent arcing there.
Here's what I mean.

At the breakerpoints a tiny bit of sparking is normal, excessive sparking is not good and indicates a bad condenser. Left condensor (1+4) is bad, right condensor (2+3) is good.
Another thing to be aware of is that the forked connectors at the back of the breakerpoints are not intermittently (due to vibrations) grounding. When installing make sure these forked connectors do not touch the baseplate. Especially breakerpoint 2+3 can ground easily as it has a crosshead real near.
The above are very simple things to check. We want to be 100% sure we have not missed what so often is the case.

[galoebi]

Do you know what’s involved in changing the basket rubbers? It’s not a job for someone without a good amount of experience with these engines. The only source I know of is in Europe and they refuse to post outside of Europe. Won’t even post to the UK.

I don't have much experience with working on these engines but is it really that complicated? Is it harder than for example replace a cylinder head? And I am from Europe so I would be interested where I could find them.

I'm not convinced yet. Here is what I'd do. Have the engine idle when it's really dark. Closely watch the plugcaps and their HT wires and make sure there is no intermittent arcing to the head. Also I'd like to see a similar video like you did, but then concentrate on the ignition plate after you've removed its cover. I'd like to see the points in action and see if there's any intermittent arcing there.

I will check that!

[Oddjob]

You'll need a pillar drill ideally. You need to drill out the rivets holding the large drive gear on the back onto the basket, this normally involves just drilling off the heads and then the steel retaining plate and the gear will pull off the basket along with the damping rubbers. That's the easy bit. Getting the remains of the rivets out of the basket can be very hard. Some seem to bond themselves in place, I've actually broken a basket in 2 trying to get some of them out. Once they are out you have 2 choices, you can use the rivets supplied by the maker of the rubbers to hold everything together again after, that's a lot harder than it sounds, even a little movement will ruin the basket in the end. Most people tap the pillars to 6mm and then you have again 2 choices. Either countersink the steel plate on the back and use 6mm countersunk screws or find some really thin headed bolts to hold the gear onto the basket. You have very little space at the rear of the basket so the bolt heads need to be under 3mm in protrusion or they'll hit the gear linkage at the rear of the basket when in situ.

In this pic you can see the 500/550 damping rubbers and how they are cracking at the corners of the forward facing edge.





This of course supposes the basket is knackered and you haven't tested that yet. I would suggest you do that first and see if it actually is.