Valves

So I'm a noob here. Not just DTT but also to internal engines as well. I'm confused as to what exactly im measuring when it comes to valve clearance. I have the manuals for both my 1977 XS500 and my 1980 CB750C but I can't seem to figure out conceptually what I'm supposed to be measuring. Is it the "gap" between the opposite of the main bulbous protrusion off the camshaft and the valve top opposite of where the cam pushes the valve? or is it something different? I'm pretty sure the CB is shimmed and the XS is adjustable without shims. I need help. If there's a thread out here already I'd love to know where that is.

If it's a DOHC, you're measuring the gap between the cam lobe and the shim. If it's a SOHC, you're measuring the gap between the valve head and the rocker, when the piston is at top dead center on that valve.

DOHC


SOHC

Got it. Thanks so much.

Please read this! The Yamaha TX500 and XS500 have a DOHC engine, but it uses screws, not shims for adjustments. The valve clearance is measured under the adjustment screw, between the screw and the valve stem.

So:
Rotate the engine to where the camshaft lobe is away from the rocker arm.
Make sure the engine is cold. (Valve adjustments on a hot engine will make the valve clearance too large, resulting in loss of power, and a clattering top end.)

Thanks so much! I did it that way and some of the noise I had encountered last riding season is gone. I wonder if that was one of the contributing factors?

Your welcome. I've been helped by many others, so just I'm passing it on. (A not so subtle hint!)

Yes, adjusting the valve clearance will quieten the engine, if the pre-adjustment clearances were too large.
There are two other sources of clattering/rattling noise on the XS500 which can be adjusted out.

A loose cam chain is one. The adjustment is easy, follow the instructions in your manual. When you loosen the dome nut you might hear a clunk. That tells you that the adjuster spring has moved the adjuster sprocket a fair amount in order to take out the slack- that's a good thing!

The XS500 balancer drive chain will loosen up and rattle too. It is a bit of work to get to the adjustment screw. And a two arm puller is required to remove the alternator rotor. But to check the tension, you need only remove the left side cover.

BTW here is a good XS500 forum : http://xs500.proboards.com/