interference engines... all makes...

[Jonathan Farrugia]

Ben

nice explanation, thats what i was looking for.  okay now for some arm
chair engineering/speculating.

i have often wondered if an engine that is a close fit interference wise
becomes interference as it ages.  i figure that as crank bearings, rod
bearings, and wrist pins wear the stroke could in effect become slightly
longer.  that coupled with the weakening of the valve spring tension
which results in more valve float as the engine gets older, thus might
make a non-interference engine become interference with age and speed.
you wouldn't see this effect unless the engine was under power so there
would be no good way to measure it.  please feel free to shoot holes in my
theory :).

jonathan

On Mon, 21 Mar 2005, Ben Swann wrote:

> This is called dynamic interference as opposed to static interference.
Static is when things will bind  due to the physical geometery of the
valves with respect to the pistons at rest - that is turning the crank
very slowly and the piston(s)  will bump up against the open valve,  if
belt not installed(correctly) or no interference when it is.
>
> In a dynamically interfering engine, the spacing may have been very
close just missing the valve, but no interference damage occurs at low
RPM, such as turning the engine over by hand.
>
> At speed(dynamic) since the valves have mass and momentum, the valves
begin to "float" and stay open a little longer and a bit farther and the
springs are not letting them close quick enough.    So if the belt breaks
while the engine is turning at higher RPM,  the valves which are not being
closed quick enough will meet the pistons in an unfriendly manner.
>
> If you install a higher lift/higher duration cam such as a 264i/254e
with around a .440 lift  you will turn the MC engine into a static
interference engine.
> Ben
>
> [Date: Mon, 21 Mar 2005 01:57:23 -0500 (EST)
> From: Jonathan Farrugia <jfarrugi at umich.edu>
> Subject: Re: interference engines... all makes...
> Cc: quattro at audifans.com
>
> can someone explain to me how an engine is not interference at idle but is
> a higher operating speeds?
>
> jonathan]