Knocking noise on idle

Hi I have a XJ550 Maxim and when it's idling there is a distinct knocking noise - I don't think its coming from the engine although I maybe wrong. The sound disappears when I rev the engine. Any ideas what it may be? Thanks in advance ;-)

 

Cam chain or valve adjustment to start, maybe loose exhaust. Could be a number of things. Some other loose part on the bike, horns , headlight to name a few. Try to see if you can isolate the knock, hold and touch parts when it is running to see if the sound changes.

 

Thanks mlew, my fault for not being clear. Sound is internal from engine area or below (more like from the gear box area)

 

There are some possibilities , stater clutch, alternator, primary drive chain. Does the knock go away when engine speed inceases, if so at what speed does it stop? Stock exhaust headers can crack internally and make knocking sounds that go away with increased speed. See if you can borrow a mechanics stethoscope and pinpiont the noise.

 

I have this same problem, the noise is only there from 800 rpm to 1200. Mine is inside the engine as well.

 

my 550 did this as well.

think it was a loose timing chain or chain tensioner. valves were in spec, and I tightened the tensioner but it made no difference.

putting a load on the engine made my noise go away as well as raising the RPM

 

change the oil and put synthetic motorcycle.

that's what took the knock at idle noise out of my ninja 600. AND, made the transmission shift like it's supposed.

most bikes don't like conventional car oil AT ALL. usually causes heavier then normal shifting. i was kinda shocked when it took the knock out of my ninja.

 

Just got done cleaning the carbs on the 1100, noticed a similar noise when the idle speed was too low. It sounds like the trans gears are rattling, it goes away with increased idle speed. After I synced the carbs and set the idle speed to aroung 1000, no more noise. Don't know for sure but I think since the engine was running rough before it made the gears rattle. Maybe its normal but who knows. Try syncing the carbs to get a smooth idle.

 

I found some guys talking about this noise, and they say that for some reason 20w50 oil helps, and "you're in trouble when you don't hear anything going on in your engine" apparently this is sort of a common noise with the xj's. Put me at ease, and I'm definitely going to put in 20w50 here soon.

 

Be careful which 20/50 you buy.

I had a long conversation with a Castrol Representative this week.
Castrol GTX 20/50 was reformulated to meet SJ Requirements.

This means there is harmful ingredients to Wet Clutches.
Select a formulation that is MOTORCYCLE USE on the Bottle.

The Castrol 4T 20/50 is recommended for Wet Clutch Bikes.

 

according to the manual. 10/30 up to 59 degrees.

20/40 down to 41 degrees.

 

I know exactly what it is.

First off, it's normal for a 550 to make that noise to some degree.

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.

 

I can also vouch for this. My XJ400 4 Cylinder uses the same primary chain assembly as is used on the 550 and makes similar noises once at idle. There is nothing to be worried about.

 

I am presently painting a 85 XJ600 and it has a knock on idle when in neutral, this goes away when the clutch is engaged, which is common with cars and thrust races, but not sure with bikes as it's been a good 15 yrs since I last restored and rode one and my first ever Yamaha.
I will be using synthetic in the bike when it's back in one piece, it's a pity Nulon (Australian brand of Teflon additive) is not suitable for wet clutches, my 27yr old Mazda 323 does not use oil and it has been run on Synthetc oil with Nulon as well and I believe it will give me many more years of service yet.

 

I have just read on Nulons web site that e20 is suitable for wet clutches as the clutches are to porous to be affected by the product