Amazing! i like this idea haha

 

If the engine physically turns, which you can hear in the video, the starter is doing it's job. It's one and only job is to crank the engine. That's why they know the starter is working because you can hear the engine being turned by the starter.

 

If the starter motor is going bad/is weak then the bendix can disengage once the motor spools up to the starter motor's max speed, right? I mean, yea, the engine is turning over, but it's got to reach a proper RPM and it can't if the starter motor is weak. And the bendix disengaging prematurely might cause the grinding that is heard. Just a thought, let me know if I'm wrong.

 

I have never seen a starter go out in the way you described. Either it turns or it doesn't. The strength in which it turns the engine is up to the charge of the battery or the ability of the wires to deliver the power necessary to the starter.

 

True. I've been told of some 3-phase motors that have failed in this manner but I can't say I've seen it either, was just suggesting it might be possible. More likely battery or cables to the starter to cause that.

 

https://repairpal.com/starter

The article says "slow cranking" but that is a function of the solenoid which can be replaced separately from the starter. That said I just listened to the video again and the engine is being turned at the correct speed it just isn't "catching" which indicates it's a problem with air or spark in my opinion. The other posters seemed to be familiar with this specific engine so I didn't bother saying so. But in general when I am trouble shooting a no start situation with proper cranking I next check for any air restrictions, then I check spark, and last I check timing. If none of these I will go online and see if there is something unique to the specific vehicle.

That said VW had a hand in this van and they do some really stupid **** with everything, I heard and episode of Car Talk on NPR where a rebuilt starter had it's solenoid wired in such a way that the pop out gear was out when not being cranked and it was pulling back in when the key was turned to start. But the OP didn't mention having just put in the starter so I can't imagine that it's doing any such thing as that or running backward as they can if wired wrong. Long story short the starter is doing it's job and nothing about the video would cause me to pull the starter and even bench test it before looking into air, spark, and then timing.

 

Then why doesn't the engine continually crank & not start as long as the key is held in the start position, assuming the starter is not the problem? This engine cranks no more than a second or two before we here the grinding noise. I'm curious to know why an air or spark issue would cause that.