Knocking noise when accelerating

[pcacton]

hi..I have a 1996 Yamaha XJ600n (20,000 miles)which has just developed a deep knocking sound which is regular and mainly noticable when in second and third gears and between 20-40 mph. The noise is only there on acceleration and stops when idling..!! have fitted a new chain and sprokets but its still there. Any ideas..
advice would be appreciated..am wondering if its dangerous to ride and what is causing it..sounds like it may be from the front sproket area...but cant be sure.

cheers

[sickpup]

Big ends.

Give a better description.

[mchaggis]

Piston slap, knackered front sprocket or main bearing wear?
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I must not be a troll...
Mmmm, Guinness
Discovering the delights of Hammerite and a 3/4" brush.

[international...]

You sure it's not the chain slapping against the swingarm?
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If at first you don't succeed, move the damn goalposts!

[stinkwheel]

Cush drive. Cush drive bearings?
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“Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.

[pcacton]

thanks for those........think i`ll take wheel/chain/ sprokets off and recheck and also have a look at the cush drive rubber.......ta..!

[Finglonga]

Try putting it in gear with front brake on, (as if you were going to do a burnout) let the clutch out enough to put the engine under load. If it knocks then It sounds like the Big end bearings are on the way out as none of the drive train it moving.
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Andy Sez....
F.Y.Y.F.F.

[pcacton]

Hi...have taken wheel off, rechecked chain,sprokets, cush drive and wheel bearings...but all are ok. put all back on and tried following last post (put in gear..front brake on..release clutch etc) but no noise was apparent. Do you think it could be something major in the engine...as said earlier..big end..main bearing? and is there any way of confirming this without stripping out engine?
Ta dudes....

[stinkwheel]

Is the noise still there?
____________________
“Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.

[bidman]

Before you go stripping your engine down make sure your not missing anything simple like loose downpipes knocking on the underside of the engine or frame etc... Then if everthings secure and its still knocking strip and check the bearings, hope this helps, Dan
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Don't ride it, RAG IT!!

[pcacton]

Thanks for all the advice.....will get christmas over, then give it a thorough check over...Cheers........Happy christmas...!!!

[loply]

Try riding a 660 single
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Yamaha SZR660 Caution to the wind, the throttle pinned!

[Knowlsey]

best way to find a noise on the engine is a large screwdriver, put the metal end to the bottom end and your ear tight to the handle, do the same at the top end, this will identify where the noise actually is

unless you have little sister who has one of those stethascope thingies in her nurse bag

they were well known to be a tappy engine, i had one for a good while, some had slight cam end play, which is not major, very rare for the big ends to go on these, only if its very high miled or not looked after, thin oil etc

[stuartevans]

My car engine did a similar thing, went to a mechanic couldnt find the problem, checked the oil and it was low. so i put some in and the noise stopped. dont know if bike engines have a similar problem, but its worth checking anyway.