Help with tappets

[jedaks]

Should the pushrods move freely only at TDC (lowest point in each of their movements) or should they move freely at any point of the piston stroke?

[Arizoni]

Only when they are not trying to open a valve.
Although this can happen when the piston is in places other than TDC, when the piston is there at the top of the compression stroke both valves will be fully closed and the pushrods will be at their maximum looseness.

I mentioned the compression stroke because if the piston is at TDC following the exhaust stroke and prior to the intake stroke, both valves will be slightly open and both pushrods will be under load and almost impossible to turn using finger pressure.

[Thumper]

These two docs might be of interest....

http://mysite.verizon.net/respud62/id2.html (section II is valves)

http://members.verizon.net/allofusmorrows/Valve_info.htm (is, well... valve info)