82 xj550 weird idling noise

Hey I recently purchased an xj550 and I have noticed that when the bike is fully warmed up I can hear a weird almost clunking noise when it is idling. the sound is muffled some when I engage the clutch, but when I disengage it the sound comes back. I also notice and can feel a clunking noise while I am slowing down to a stop. (feels and sounds like its coming from the engine). At high rpm's this bike purs and I love it. I was thinking it might be a problem with the primary chain or a broken seal. any ideas?

 

Welcome to XJBikes! You've come to the right place.

Check your valve clearances - if you have a tight valve, very strange noises can result. How many miles are on this bike?

A properly tuned 550 will have a slight whirring sound at idle, so it depends on how loud the noise is etc.

Before you ride ANY further, check your rear brake shoes- after 30 years, who knows what state they are in. They can come UNGLUED and cause a whole ton of trouble.

 

Sure.

It's normal. How pronounced it is is a function of the oil you're running, and the state of tune of the motor.

What's happening is this: the primary chain on the 550s is a "true" primary chain in that it is actually the primary drive from the motor to the clutch and transmission. (Unlike the shafties that have a geared primary.)

As such, it is hydraulically tensioned by engine oil pressure. At low RPM, the tensioner relaxes and allows some slack into the chain. It goes away as soon as you rev it, because the oil pressure comes up.

That's where the oil comes in. If you run the recommended 20W40 or even 20W50, the tensioner will be less "relaxed" at idle than it will with 10W-basis weight oil.

And the state of tune: An out-of-sync XJ engine tends to idle with a "lump-lump-lump" rhythm; which means that the crankshaft is not rotating smoothly. That lack of smoothness gets transmitted to the slack-at-idle primary causing the chain to "slap" plus rattle the gearbox guts if the clutch is out and the bike in neutral. Pull in the clutch and it lessens a bit because the tranny is no longer involved.

If you get the motor tuned and synced properly, you can eliminate the "lumpy" idle and get the bike purring like a sewing machine. Doing that greatly reduces the primary slapping sound.

Adjusting the valves is just the first step in getting the motor properly tuned and synced, and idling smoothly.

 

Thanks for the great answers guys.. I remember the last owner saying he replaced the valves, so I'm sure he might not have adjusted the vavles accordingly.
I'll get those checked out! thanks

 

I highly doubt he replaced the valves; more likely the valve shims. (That's how you adjust them.)

They're only the first step toward a smooth idle.