Knocking sound at slow idle...smooth everywhere else

[Jim_in_Calgary]

I noticed on my 03 Sprint ST that I have a knocking/strong clicking sound at idle. ...every second or second and a half.

I can really hear it if I lean over the tank sitting at light once the bike is fully warmed up. ...less if I lean back.

It goes away above 1200 rpm, and sounds like a nut is randomly banging around in the crankcase or something.....it's pretty hard to describe.

It's not the smooth idle sound I'm used to on my FJ1200....but when I rev it up it feels great!

Anybody know what this could be? I thought it might be clutch chatter or something, but it doesn't make a difference clutch in/out, in gear or neutral.

I read somewhere it could be throttle body (butterflys) flapping due to throttle bodies out of synch...it sounds clicky/rattly like that. It's not a muted sound, it's a sharp intermittent clatter....only at slow idle.

The bike has 19k miles on it, and I don't know the service history. I just got it 2k miles ago.

Otherwise it runs strong, and feels like it makes about he same power as the fj1200 (dyno'd at 120 at the rear wheel).

But ohh....the Sprint can HANDLE...and it's one great looking bike!

Anyhow...does anybody have any ideas what this sound could be? A little disconcerting.

Thanks in advance!

[ This message was edited by: Jim_in_Calgary on 2005-06-17 00:50 ]

[SpiderTex]

Clickety sound, rather stable? When you slowly rev, does the clicking frequency increases?
If yes it might be related to wear on the bearings (glide bearings) around which the piston rods grip (on the crankshaft) *sorry the correct English terminology escapes me, it's my Friday's Alzheimer :hammer: *
or something getting whisked along with the crankshaft.

Does the sound stay when pulling the clutch?

Does it rattle in gear, while driving?

The more you describe the better others can help narrowing the problem down.

So, probably it is something benign... see what the others say...

[mattbin]

Sounds like an expansion/contraction thing to me. At the rate of one a second I doubt its engine related i.e. bearings. Solenoid? Does it do it if you turn the engine off, does it increase with engine revs. If you bought it at a dealer, why not take it back under warranty, either Triumphs or dealers.
Does it go away when you lean back because your crash lid is pushing against your ears.

Matt

[Jim_in_Calgary]

To answer a few questions:

- The sound is totally random, and unrelated in any way to engine revs.

- When idle is raised even 200 rpms above slow-idle, the sound disappears....and the engine sounds very smooth at anything above low idle.

- it's an intermittent clicking/clanking sound that might occur every second, followed by in a second and a half, followed by in half a second if that makes sense.

- it does not sound like anything within the rotating assembly such as a bad bearing in the piston rod end-caps (I hope).

- clutch in vs. out makes no difference, you hear the rattle either way

- the sound disappears while driving.

- it's definitely not an expansion/contraction noise...I know what that sounds like and this noise is too loud for that, and does not carry on if the engine is stopped. Expansion, contraction noises generally do in my experience.

- it might be wishful thinking, but it does really sound like the sound butterfly valves would make if they were slapping open and closed randomly.

- What I meant to say about leaning back/forward is that the sound is more apparent when my ears are closer to the front of the engine, rather than the rear.

- MATTBIN mentioned the solenoid. Are we talking about the starter soleniod being shorted perhaps? I would expect to have a grinding sound as the starter gear engaged the flywheel, and I don't hear anything like that. Are we speaking the same language?

I really should take it in, but I'm not fond of my local triumph dealer.

Please keep the thoughts coming..I very much appreciate everyone's input!

[mattbin]

When its making this noise does it go away if you turn the engine off (using the key obviously). Solenoid? I'm thinking any one of them, rather than just the starter, as you say you would hear an orrible noise if it tried to engage I think, might try it later to see if there is an inhibitor in the circuit, unless someone already knows.

I spun my rear whell recently, it made a noise, a knocking noise, it was a loose transponder, we use them in the UK to prove ownership (or otherwise). Dont suppose you have them over there, maybe in the engine/box that may have come lose.

I wonder if its something to do with the fuel system, a light load causing some sort of relief valve to open, you guys have closed loop systems dont you, so excess fuel gets pumped back into the tank. Is it that which is causing this noise. Increased revs might mean excess is being burned away so not being sent back.
There was a mod to up the pressure on this site, does that cause this effect. I'm still running normal fuel pressure so I wouldnt know.

Matt