Knocking sound at low revs

[bluedayt]

Found the problem guys. And it was a damned simple one too. The noise I was hearing was the timing plate bouncing back & forth in time with No. 2 cylinder. After a bit of searching through the US XS11 site I'd found some guys talking about where the air lines need to go. That's when i found the bloody vac line was connected to the wrong spot. Instead of being connected to the Carb it was plugged into the inlet manifold.  I swapped it over with the Octopous line and hey presto, beautiful quiet smooth. The rough idling has gone, it reves nice & cleanly as well. Beautiful. This bike wasn't running when I bought it and I'd just asss - umed those hoses were connected right. I guess it never pays to assume huh.... And if all else fails, read the instructions

Thanks for all the advice guys and sorry to have wasted your time.

Cheers

[petejw1966]

hi blueday,

like you said, sync the carbs first and see how that goes, ive got a clapped out main bearing
that you can hear from the timing cover, the more out of sync the carbs
are the worse it sounds.

[bluedayt]

Thanks for all your repies guys. I need to let you know this bike is a 'project' i'm working on having ready by spring. It's needed a lot of attention before its ready, but I'm getting through the list.

The bike idles very roughly but I haven't balanced the carbies yet. The sound disappears over 1500rpm, which is telling me to sort the carbies out then see if the noise is still there before I go down the bearing path.

I've got a KTM enduro bike and you have to run the chains real loose on them. The slaps around quite a bit when your backed off &going over rough terrain. The sound in the XS reminds me of that noise

I'll sort out the carbies over the next few weeks & let you know what the outcome of that is.


Cheers

[Christian Raith]

Does the bike feel smooth or rough? Is it just that it doesn't sound right?

Leaking exhaust gasket?
Just a thought as I went through a time I thought I had a BIG problem in the motor and it was the flange one of the header pipes that was cracked.

[steptoe]

is the knocking a low bass or more of a rattle?

the hyvo chain would have to be way worn to make any noise, it's normally bathed in oil,
cam chain rattle is cam chain rattle--which sounds exactly the same as piston slap in my experience,, that's what mine was making,that's when I put in 2nd o/s pistons,

clutch rattle can be a bit off putting at different times, not hard to fix,,

at 170 000 klm most likely to be bearing shells, not knowing maintenance schedule and oil used,, although listening to Errol 170 is chicken feed

THE FIRST THING TO DO,  take the filter out, and take it to a reputable mechanic, they have a tool that can cut the paper out of it, if they don't know what your talking about move on to the next, until some one knows what you want, they squeeze the paper in a vice to get rid of all the oil,, then open the paper on a bench and go thru the metal that's left,,and will be able to tell you your problem

that will be the easiest and cheapest place to start with out just ripping into it and finding out you didn't have to

[pgnz]

OK,  an XS11 runs a primary chain direct from the crankshaft to the starter clutch shaft.  That starter clutch shaft has a U-joint and stack of spring washers that gives a bit of slop to the shaft to absorb the shock when you hit the throttle.   No hydraulic oil pressure tensioner in there though,  the chain is a massive hyvo type,  but gets a bit of slack eventually,  but shouldn't be making a horrendous "worrying knocking sound".... 

 Worrying knocking sounds are usually something bad news and evil like worn crank bearings or piston slap, or shagged big end journals/bearings..    Whip off the lower left cover and turn the timing plate to the C mark and tension up the cam-chain to see if the sound gets better..   Balancing the carbs gives 4 even pulses that balance the spinning clutch, and when the clutch is balanced the whole engine runs smoother.  Good luck!

[melbxs]

Mine will be rego'd next week if all goes well. I can pop down for a cuppa and we can compare clunks, knocks and rattles.

[bluedayt]

Hi Brian,

Great news, thanks! All i've done is drain the bowls since I got it & it is quite rough when cold. I'll get them balanced & let you know how I go. It also has a slight gurgling sound as well, which makes sense if the primary chain is tensioned by the oil pressure.

Thanks for your help, I'll let you know how it goes

[melbxs]

John,

Here's an explanation of the same noise on an XJ550. Hopefully it's the same on the XS. Apparently balancing your carbs makes a big difference because it smoothes out the idle.

The 550 uses its Primary Chain to drive the gearbox (unlike the bigger bikes where it's only for the starter and alternator.) This "true" primary chain is hydraulically tensioned using engine oil pressure. This is why the sound goes away or is greatly reduced as soon as you rev the engine.

What you are hearing is primary chain "slap."

The sound will also be less prevalent when the motor is cold (and the oil thick.)

The effect can be GREATLY REDUCED by getting the bike properly tuned, and taking the "lope" out of the idle. If you get the bike so it idles like a sewing machine, the primary chain is much happier.

It's not a cause for concern.

[bluedayt]

Well, I'm close to getting the old lady back onto the road but there's a worrying knocking noise low in the front of the motor. The noise disappears when the revs build, but are always there when idling or a bit more. I'm not sure of the mileage, but think its around the 170Km. Would it be the Primary chain slapping around?

Cheers, John