valve timing question?

[tolson]

i installed a web cam and i don't understand what they are saying here, "Valve timing is checked with zero valve lash @ 0.050 inches of valve lift."

i put a all around web cam and heavier springs in and have adjusted the valve clearance at .004 at TDC, but i don't know how to do the above?

anyone?

[MIKE400EX]

Measuring the valve timing with 0 valve lash @ .050' lift is the US standard for measuring and verifying the valve opening and closing events. It is a lift point to start measuring from that eliminates the initial ramp portion of the cam lobe, ie..it sets a reference point that "everyone" can use so that you can make meaningful comparisons between cams. The installer can use the numbers to degree the cam in, although there's not much way to change the cam position other than slotting the cam sprocket mounting holes. You don't need to be concerned with those numbers if you are only adjusting valve lash.
Are you sure that the valve lash is supposed to be .004" on both Intake & Exhaust?

[tolson]

thanks mike, web cams instructions say to adjust both to the same measurement.:D

[TC426EX]

usually there is a difference between the intake and exhaust settings. I know stock and most aftermarket cams are 5 and 7 thousandths...

[cals400ex]

Originally posted by TC426EX
usually there is a difference between the intake and exhaust settings. I know stock and most aftermarket cams are 5 and 7 thousandths...


is this what you ended up running with that TC cam?

[tolson]

my stock valve springs were different colors and probably different clearnances, but the web cam instructions said the same clearances for both. make sense?????:confused:

valves are making a little more noise than stock, but they have been adjusted after running and are good.

[MIKE400EX]

It's certainly possible to grind a cam that uses the same clearance on both I & E. It's just not common, usually the exhaust side is .001" more on these motors. I'll try to find my old 450/451 sheet and see. The rockers/cam will make a little more noise than stock since the cam is a bit more aggressive - not much more noise though.

[wilkin250r]

I think you might be confusing things.

There is a difference between valve adjustment and clearance, and valve timing.

For valve clearance, you set the piston at TDC so that both all valves are closed, and the rockers and valve are in the correct place to make the adjustment. You then give a specified clearance (it sounds like .004"). The reason for this clearance is that the valves shafts will get longer as the engine warms up (because heat causes things to expand). If you have no clearance at all when the engine is cold, the valves will get longer and then they won't fully close. If the clearance is too big, the rockers will hammer against the valves, shortening the life of the rockers and valves.

Valve TIMING is another issue. Obviously your cam controls your valve timing. In order to compare different cams, the timing must be measured the same way. A person could argue that the valve is not truly "open" at .010", since you aren't getting any meaningful flow when the valve is only open the thickness of a few pieces of paper. So they determine "open" at .050" using zero valve lash. That specification is only used to compare cam specifications, NOT to be used to make valve adjustments.

[tolson]

thanks, i'm going to email web cam too.