Valve lash - overthinking..

[grandfatherjim]

Setting valves, and once the covers are off just out of habit I wiggle the rockers. Several are way wide by about the same amount...why would this be? I'm used to them gradually tightening up, or I can imagine them being off 0.001 or 0.002 due to inaccurate setting previously, but these were like 0.010" instead of the specified 0.006".
Turns out they are way wide when the other valve on that cylinder is opening - but are at spec. when the cylinder is at TDC.
Seems to me as though my cam has indented sides.
So, now I begin to wonder....If I set them to spec with cylinder at TDC, does this mean the valve is then opening late and closing early? Conversely, if I set them to spec. when the other valve for that cylinder is opening, will it be too tight when the cylinder is at TDC? (In the latter case there is still a gap, but barely, with the cylinder at TDC.) And part b) to the second scenario, does the combination pushrod/cylinder head expand more than the valve stems once the engine is hot i.e. does the gap widen?
Jim

[SlowLane]

Setting valves, and once the covers are off just out of habit I wiggle the rockers. Several are way wide by about the same amount...why would this be? I'm used to them gradually tightening up, or I can imagine them being off 0.001 or 0.002 due to inaccurate setting previously, but these were like 0.010" instead of the specified 0.006".
Turns out they are way wide when the other valve on that cylinder is opening - but are at spec. when the cylinder is at TDC.
Seems to me as though my cam has indented sides.
So, now I begin to wonder....If I set them to spec with cylinder at TDC, does this mean the valve is then opening late and closing early? Conversely, if I set them to spec. when the other valve for that cylinder is opening, will it be too tight when the cylinder is at TDC? (In the latter case there is still a gap, but barely, with the cylinder at TDC.) And part b) to the second scenario, does the combination pushrod/cylinder head expand more than the valve stems once the engine is hot i.e. does the gap widen?
Jim

Wow. Interesting observation, Jim, and not a little bit worrying.

At first blush, it seems that your camshaft's base circle might not be perfectly circular, but can you elaborate on just what you mean by "opening"? Like how far opened? Y'see, at TDC, both intake and exhaust on the oppoisite side are open a tiny amount during the valve overlap phase. Visually, this means that the camshaft is positioned so that the "valley" between the intake and exhaust lobes is pointed towards the opposite cylinder at TDC. The lifters for the cylinder you are measuring aren't contacting the camshaft at 180 degrees from the camshaft lobes, but rather more like 140 degrees or so. When you turn the engine so that the opposite valve is opening, then you're moving the lifter contact for the valve you're measuring closer to the 180 degree mark.

It really shouldn't matter, though, as the base circle is supposed to extend for at least 180 degrees of the cam's profile. Is this a factory cam? Aftermarket? How many miles on it?

I'd set them to spec at TDC, as you've been doing. Much better to err on the side of being too loose than being too tight. The valve clearance does lessen as the engine warms, which is why we're told to adjust them cold.

[Amskeptic]

Setting valves, and once the covers are off just out of habit I wiggle the rockers. Several are way wide by about the same amount...why would this be? I'm used to them gradually tightening up, or I can imagine them being off 0.001 or 0.002 due to inaccurate setting previously, but these were like 0.010" instead of the specified 0.006".
Turns out they are way wide when the other valve on that cylinder is opening - but are at spec. when the cylinder is at TDC.
Seems to me as though my cam has indented sides.
So, now I begin to wonder....If I set them to spec with cylinder at TDC, does this mean the valve is then opening late and closing early? Conversely, if I set them to spec. when the other valve for that cylinder is opening, will it be too tight when the cylinder is at TDC? (In the latter case there is still a gap, but barely, with the cylinder at TDC.) And part b) to the second scenario, does the combination pushrod/cylinder head expand more than the valve stems once the engine is hot i.e. does the gap widen?
Jim

Set them at TDC for that specific cylinder only. Yes, the clearance appears to be wider at other locations most usually because the camshaft has lateral movement in its bearings (up to .003" with a worn engine) depending on which lifters are being shoved by whose valve springs.