Hi Ho Silver... away! What noise is this!!

[onchiman]

I've been tinkering with my '79 GS850 and have noticed a pronounced noise when the engine is warm. It doesn't happen so much when the engine is cold or fully hot. It's most noticible after it's been run for a while, sits for a half hour and then is restarted and idling. It's then that I hear a noise that has a rhythmic tapping. I've removed plug wires one at a time while the engine is running with no change. I've also used a mechanics stethoscope that my Grandfather left me years ago and the sound seems to be emanating from the camshft. More specifically, the exhaust camshaft right side. The sound is like "giddyap..giddyap..giddyap..giddyap". Sort of like if you tap your ring finger, middle finger and index finger on the table quickly over and over. The noise dissappears above 2500 rpm. Is this cam end float perhaps or is it time to look into valve shim adjustment?

[Steve]

Might be end float, as the need for valve shim adjustment is usually announced silently. MOST valves will tighten their clearances over time, so the little bit of clearance that there is, will slowly go away. If the clearance is not checked, it can lead to burnt valves or valve seats, which is a LOT more expensive than the time it takes to check them every so often.

Also, because of the power characteristics of most bike engines (over-powered, compared to cars), you can broaden the torque curve a bit by adjusting the valves to the outer limits. If the specs call for .002-.006", set them for .006. Peak horsepower might be down one or two, but the torque curve will start a bit earlier, making it much more street-friendly, and it will go longer between adjustments. The trade-off it a bit more valve noise, but, hey, it's a bike. It WILL make noise. \\/


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[chef1366]

Move your tach cable and see if that's it. If not probably valve adjusment or worn cam lobe.

[onchiman]

I'll check the tach cable/gear, I hadn't thought of that.