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1990 xj600 valve noise (i think)


EPP
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I'm getting there with my bike...

Exhaust - done

Starting - sorted (overhauled carbs, replaced caps and plugs)

Brakes - bedding in

So, I took it for a ride the other night and noticed the engine was making a kind of buzzing noise, or high frequency rattle, at about 3-4000 revs (I was bedding in the brakes so didn't get much above that). I've since had a listen with the bike in the drive, and it sounds like it's coming from the cam chain or the valves. Seems okay at tickover and just above (where the clutch rattle comes into play - but that's another story). If the engine is revved, the noise kicks in and then recedes as the revs drop.

I'm going to adjust the cam chain tension first, then check the valve clearances and valve spring, as suggested in the manual.

Bearing in mind the bike was stolen and most likely ragged about the local park before being recovered, what other things might I be looking for?

Cheers,

Ewan

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Valve clearances - fine

Cam chain tension - well, it seems pretty tight to me. Can't imagine it slapping around.

I've been tinkering with the cam chain adjuster, but I can't see how it changes the tension. It seems to operate as a lock screw for the spring mechanism rather than something that adjusts the tension directly. Am I missing something?

I've replaced the dowel pin on the oil drive gear at the back of the clutch. Very little play there now, so hopefully that'll cure the clutch rattle.

But seeing as I've not found anything wrong, the rattle that seems to come from the valves will presumably still be there.

Any suggestions much appreciated!

Ewan

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Did you adjust the camchain with the engine in the correct position ? If you take off the LH side crank cover you will see a C mark on the ignition rotor which you line up with the line on the upper pickup coil turning the crank in the direction of rotation i.e anticlockwise using the square on the end of the ignition rotor not the allen bolt.Then loosen the locknut on the camchain tensoner and then the bolt. This releases the spring loaded tensioner rod and takes up any slack in the camchain.Retighten the tensioner bolt to 8Nm and the locknut to 9Nm. Hope this helps. Tony.

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Yeah, I lined up the marks (I've got the later model that required you to line the C up with the mark on the crankcase). The manual didn't say to loosen the bolt to release the tensioner first - that's the vital bit of info I was missing. I had a hunch it might be necessary, thanks for confirming!

I wonder if that will have fixed the rattle. Need to replace some bits of the clutch and refill with oil before I find out...

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Repaired the clutch, refilled the engine with oil and got the bike running today. No rattle!! So it looks like it was the cam chain.

Unfortunately, a short way into the test ride I noticed a regular knocking sound coming from the engine, in time with the revs. Could be felt through the bike and heard at tickover, but not audible at higher revs (may just be drowned out). The knocking wasn't there when I first started the bike, only when it had got pretty warm.

Got the bike home, and when I listened to the engine it sounded like it was coming from the cylinders (I just put my ear near - have since read about using a screwdriver as a stethascope to help locate the noise more accurately. I'll try this tomorrow). No idea if just one, or more, cylinders involved. I also noticed the engine was hotter than usual, or seemed to be anyway. I had already topped the oil up after running it for a few minutes to fill the filter etc, but it needed another 300-500ml on returning from the test ride, and a vapour rose from the crankcase when the cap was removed - definitely seemed hot!

Could this just be the result of low oil? How much below the recommended level would cause overheating? And would overheating lead to the knocking noise?

Cheers all,

Ewan

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