Would the original 2.1L opposed four engine in this vehicle be considered an "interference engine" or not?
A) It doesn't have a high compression ratio...maybe 8:1...so probably not an interference engine. B) it's not an overhead cam engine, it's cam is internally driven...no timing belt to break. Not much chance of the valves getting out of sync with the pistons.
No. Interference engine means that the piston could contact the valves. Generally this is used with engines that have timing belts that can break, allowing the valves to be fully open where the pistons can strike them. No worry with this situation in a Vanagon since it is a pushrod engine. Also, I don't believe the valves would hit the piston anyway, given the design of the engine.
The opposed four is definitely an interference engine because if a valve stuck open it would hit the piston. The term really doesn't apply though, because it is usually applied to OHC engines with belts or chains.
The whole reason engines are categorized as "interference" is due to modern engines having high compression ratios. This means the crown of the piston gets closer to the combustion chamber roof than a lower compression engine's pistons would. A sufficiently low compression would mean that even if the timing chain/belt or whatever let go, the piston crowns would not impact the valves which are still kept in position by the camshaft lobes and valves springs.
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