[olddog]

Originally Posted by blykins

As I said, if you can guarantee that the lifters are on the heel, it's perfectly fine.

However, I have used the TDC method and the EVO method on a solid cam engine before for comparison, and got about .002" difference. With the EVO method, I can guarantee that the lifter is on the heel of the lobe.

With the EVO/IVC method, you set the intake valve when the exhaust valve is opening. When the exhaust valve is starting to open, you've had a power cycle and you're starting to push the exhaust out. There is no feasible way that the intake valve could be open at this point. On the flip side, you set the exhaust valve when the intake valve is starting to close. When the intake valve is starting to close, you're somewhere in the compression stroke. The cam dictates at what point that intake valve starts to close relative to the piston on this stroke. However, it's not possible that the exhaust valve could be open at this point.

If you look at that transition from the compression stroke to the power stroke that you were referring to, depending on the cam, it's possible that the intake valve could still be off the seat, even by a minute amount, due to the IVC event (the same principle that gives us the DCR relationships), especially with 82° of overlap, which Wayne's cam has. The other transition from the exhaust to the intake stroke will absolutely almost guarantee that one or both valves will be open. If you happen to try to adjust the valves there, you will get a discrepancy.

Also, with the EVO/IVC method, you can literally hop through the entire bank of cylinders in just a couple of minutes if you pay attention. While you're watching one exhaust valve starting to open so that you can set the intake on one cylinder, you can keep your eye on the intake valve starting to close on another cylinder, so you can hop right to that exhaust valve. It takes no time at all.

Thank you for the explanation. I understand now.

I was thinking it would take over 360 duration on the intake for the valve not to be seated at TDC on compression stroke. However I forgot that the 0.006 inch lift duration does not include all of the ramp. With Wayne's 5 O'clock method he was close to TDC but not exactly. Actually quite a bit of error possible. Now I see your concern.