Another rattle thread

luckynumber0

luckynumber0

In Over His Head
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Hey guys,

Been reading a few of the "help! my engine is rattling" threads but am still scratching my head here on my '82 650 (stock except for K&N pods on the carbs, some aftermarket mufflers, and a rejet to compensate for them)

It's a new rattle in the top end. I adjusted the valves & cam chain to manual spec but it didn't seem to help at all. It's intermittent, happening only at high RPMs (engine braking, a burst of throttle) and - as far as I can hear the rattle doesn't happen when I'm cruising. I noticed it two days ago. The bike is my daily driver but there was no noticeable change in the performance of the bike nor did it get worse. When I noticed the rattle I stopped riding it around.

It sounded like maybe a tappet locknut had come off and was floating around in the adjustment bay, but when I popped off the covers everything was fine. That's the sound though - like a loose nut rattling around somewhere.

No chunks of metal or plastic in the oil as far as I can tell. Some metal dust stuck to the magnetic drain plug.

What do we think? Has the cam chain guide finally worn through? Is it the chain itself? Stupid question, but there's no chance in hell it's safe to ride to work tomorrow morning, right?

Thanks,
Lucky
 
^ that's a damn good thread. I'll check 'em tomorrow morning. Thanks!

Did quite a bit of reading on here all day and my head is spinning with all the possible causes making me want to just rebuild the whole damn thing to be sure. I think the old speedo that it came with read ~30k but it was broken when I got the bike (barn find).

Hard to make my own video to show ya'll the sound because it's most pronounced when I'm engine braking - it only kinda happens in idle when it winds down from quick burst of throttle. With my loud pipes it kinda muddles up the cacophony.

Sad to say, but it sounds like this:

But NOT just chilling at idle like in that video, and also not constantly. ONLY when I engine brake or otherwise bring up the rpm's to make the engine really vibrate.
 
The audio doesn't come over very well on my smartphone. My overall impression is sharp valve pop (like from worn rocker fingers) and too high an idle (like from shortened valve timing). It sounds strained, like it'll run with reduced power (also can be caused by worn rockers). Might want to flashlight around the cam and look for wear signs...
 
So I unscrewed the valve adjustment tappets and both they and their contact point on the valve stems are pitted to various ends...Left side intake being the worst. Definitely time to replace them, likely with a lot of the top end parts as they're seen a ton of miles.

However, I as I was resetting the tappets back to spec clearance after the inspection, I believe I figured out *when* the noise was happening - though still not where.
It happens here:

Va5CQEC.jpg


Every time. Very subtly when I hand crank the engine counterclockwise. I heard no tick from the tappets despite how warn they were. When I half-crank it past that point (kind of lean on and off the ratchet turning the crank so it goes, stops, and goes), I hear the noise until right about the timing mark.

What exactly happens there? Where could the noise be? Timing chain? Thrown bearing? Busted circlip floating around?
 
Last edited:
At TDC, valves on one cylinder are loose. On the other cylinder, its valves are at overlap, intake is starting to open and exhaust is almost closed. Those valves (because of their valvesprings) will be trying to push the cam back to TDC, fighting the crank by way of the camchain, and if you're jiggling the crank slightly near TDC, the camchain could be slapping the camchain guide(s).

Unfortunately, worn wristpin(s) can be detected similarly at that same TDC. But they'll make more of a 'tock' sound, more easily heard with a tube (held to your ear) that's been shoved into the sparkplug hole.

To be really sure of the camchain, it's best to use a mechanic's stethoscope with the probe touched to one of the front guide's 6mm bolts, and duplicate that crank movement that you did to get the sound.

Actually, if you're going to spring for a stethoscope, probe around on the running engine to better pinpoint the sound's location.

It's a great tool, just takes time to learn the sounds and figure which are ok, and which aren't. If you've never used one before you may be convinced that everything needs to be replaced. A good way to learn with it is to probe around your car engine, especially the backside bearing of the alternator. It's loud, but that's normal. Many alternators were unnecessarily replaced because of their loud bearings. (Truly bad bearings are deafening).
 
Did both tests today! The rattle was picked up with the probe at the 6mm guide bolts. It's slight, and being new to all of this I wasn't sure if it might be a 'normal' noise, but when I duplicated the test on another xs650 I heard nothing all.

I guess my next thread is going to be "My Engine Rebuild!".

I'm kind of excited! I'll have to save up some cash, but it's always been a dream of mine to ride a brand new xs650. I want to see how close to mint I can get with it.

Thanks for all your help
 

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