Topic: CB 500 Rattling/knocking noise on idle, video included

[Kasper]

Hello all,

I hope someone can identify my problem from this video :
youtube.com/watch?v=iSx070Meomk&feature=youtu.be

So my Cb 500 four is rattling/ knocking/ clonking when running at low rpms.


Once I rev it up approx. past 1600rpm it smoothes out, and revving the bike
harder reveals no additional noises, it then runs beautifully.

I am not sure about this, but it could be that the problem starts when the
engine is warmed up slightly?

I have so far:
-Set the valve tappet clearances
-Cam chain auto adjustment per manual
-Changed new spark plugs

Can someone make out what the problem could be?

-Kasper

[dave500]

the carbs need to be vacuum syncronised,after you go right over the ignition,i didnt even look at your video.

[Kasper]

Thank you for your quick reply.

Just to clarify:

So I should in your opinion check the ignition components (points, condensers etc.) first,
and then do a vacuum sync?

The noise made me first worry about a worn camchain, but I quess the rattling should not go away
at higher rpms if that was the case, or am I wrong?

[dave500]

yeas,get your ignition in tip top shape,use a timing light to set it,make sure the air filter is good not just looks good,if its very old but looks clean itll need repalcing really,,then do the vacuum sync,,when the sync is out of adjustment itll sound exactly as you describe at idle,,they sound terrible but come good as the rpm increases,then terrible again at idle,,the sync will solve that for you.

also be sure the idle speed setting isnt too low,,dont go by the tacho reading go by the sound and feel of it.

[Scott S]

 Everything that Dave said, +1.

 Set the idle up a bit, too. 900 rpm is too low for these bikes. Set it at ~1050-1100. Some bikes even like a little closer to 1200 rpm.
 Out of sync carbs can make a bike sound awful.

[iron_worker]

Guys, I don't think that's a carb sync induced noise.

The fact that it happens at a specific RPM makes me think it's chain whip hitting the case. If it were due to carb sync it would just get worse and worse as the RPMs went down. If it were a bearing knock it would get worse and worse as the RPMs went up.

Just my $.02.

Pull the pan and check for aluminum shavings. If it is whipping that bad there will definitely be some bits.

IW

[Smoke Detector]

+1 with Dave on this one, do everything on the 3000mile tune-up in order, vacuum sync last on the list. Mine currently sounds exactly like yours because I haven't done carb sync yet. I even checked the cam chain tension again because I thought I must have done it wrong the first time. I read other posts on this site which said that they will sound like that until you sync the carbs.
Edit: also adding to what IW said, this is not from my personal experience but I've also read that un-synced carbs can make even a  properly-tensioned cam chain hit cases at idle. So after sync, if the noise is still there maybe there's another problem.

[Grabcon]

My kids CB550 has the same noise and I will say that syncing and raising the idle does help the noise disappear, But it still does not resolve what is making the noise. I have found that if I disengage the clutch the noise goes away. The bike has about 28k on the clock.

I would like to say it is either a clutch or primary chain noised. But until I dig into it I won't know for sure.

[Fritz]

Here's what I've learnt about this issue from own experience and reading through many threads on this forum:

1) The primary chain on the CB500 and CB550 does not have a tensioner - therefore it will always have a bit of slack
2) In neutral, with the clutch engaged/'connected', the clutch basket and transmission is constantly accelerating and decelerating with the idle RPMs causing the rattling/knocking noise
3) Loose rivets on the clutch basket, axial play of the clutch and hardened damper rubbers on the primary shaft can add to the noise
4) A new primary chain will only provide a temporary 'cure' for the problem since it will become streched again soon
5) Running a poorly tuned bike will increase wear of the primary chain, so you should keep your motor tuned up
6) The motor should be idling around 1050rpm, not below
7) A badly worn primary chain rubs on an oil channel leading to the oil filter. If this channel is rubbed through, desaster will happen
8 ) If rattling noise disappears above 1500rpm in neutral, there's no need to worry - just keep the motor tuned up
9) While changing the primary chain, the "once you are in there" effect will appear leading to more work and money spent than planned  So if 8 applies, just leave the motor closed and keep the it tuned up

So what can you do?
Well, give your bike a - you already kown that:
complete tune up in the order a) valves - b) cam chain - c) point gaps - d) ignition timing - e) idle mixture - f) carb synchronization - g) idle speed
The official Honda workshop manual downloadable on this site is your friend.

And of course, your bike is always thankful for an unclogged air filter and fresh oil

[DustyRags]

What Fritz said. Listen to all these guys, especially Fritz and Dave. They got me running in top-top shape.

(and then I was an idiot and sold the bike, but that's probably for the best in the long run)

[Duanob]

Guys, I don't think that's a carb sync induced noise.

The fact that it happens at a specific RPM makes me think it's chain whip hitting the case. If it were due to carb sync it would just get worse and worse as the RPMs went down. If it were a bearing knock it would get worse and worse as the RPMs went up.

Just my $.02.

Pull the pan and check for aluminum shavings. If it is whipping that bad there will definitely be some bits.

IW

It does get worse as the RPMs go down and virtually goes away when revved up. The carb sync is only good for idling. When the carbs are not synced they cause the cylinders to fight against each other instead of working together. Thats what causes the primary chain to jump around in the cases. The 550 does not have a primary chain tensioner so requires a good carb sync to keep the primary chain as tight as possible.  My 550 sounds just like that after I bench sync the carbs and install them. After a good vac sync it pretty much goes away. Unfortunately the 550 motor is a noisy one anyway even when perfectly tuned.


BTW I don't think the auto adjustment method works all thet well. I use a little force by turning the cam tensioner adjustment screw CCW while tightening the nut. That really quieted my motor down.