interference engines... all makes...

Ben Swann benswann at
Mon Mar 21 10:34:47 EST 2005

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.


[Date: Mon, 21 Mar 2005 01:57:23 -0500 (EST)
From: Jonathan Farrugia <jfarrugi at>
Subject: Re: interference engines... all makes...
Cc: quattro at
<Pine.SOL.4.58.0503210155460.8519 at>
Content-Type: TEXT/PLAIN; charset=US-ASCII

can someone explain to me how an engine is not interference at idle but is
a higher operating speeds?

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