Originally Posted by embee (Post 2188790)

It's a standard development check to determine valve rotation vs engine speed to ensure satisfactory rotation. You don't want excessive rotation as it can lead to seat wear but you do want some rotation to take place during the normal engine speed range to maintain clean seats and good sealing.

You quite often see rotation reversal too, the graph of valve rotation vs engine speed can be a bit like a hockey stick, dipping negative then going positive as speed increases.

The driving force behind valve rotation is the balance between spring helix angle and usually valve tip/follower friction. At low speed the tip friction will usually prevent rotation, as speed increases the inertia unloads the contact at full lift and rotation begins earlier in the lift cycle so rotation rates increase.

For lower speed engines it's common to introduce low friction elements into the system in order to promote rotation at low speeds, first is multigroove collets which don't grip the valve stem (often only on exhausts), for very low speed engines positive rotators can be used ("rotocoil").

Interestingly the short pivoted finger follower as in this case is usually the lowest inertia design so most suitable for very high speed valve gear.

Good game.

Originally Posted by Alpinestarhero (Post 2189174)

Embee, what is generaly considered to be a "low speed" engine?

Originally Posted by yorkie_chris (Post 2189388)

Huge diesels, stationary engines, industrial stuff. Maybe big gennys, compressors etc.

Originally Posted by Nobbylad (Post 2188657)

Wife just walked in, I'm sat there smiling like a Cheshire cat and she's like....WTF?! "You're looking at some metal making noise?".......wimmin:rolleyes:

Originally Posted by yorkie_chris (Post 2189697)

move your hand up and down 230 times a second, with all that jailbait you're not shagging i bet that won't be difficult:smt081