[pothole]

My guess is that the pump they sent is for the 987/997 series / M97 engine.

I replaced the pump on my 986 last year with an official Porsche part and had exactly the same problem. The pump bolted up to the block perfectly but the impeller caught the block.

Turned out I had been supplied the wrong part. I had noticed the part number on the box started "997" when most parts for 986's start "996", but assumed that some parts were cross compatible and in those cases they'd ceased supplying the earlier part.

But no, it was the wrong part.

What was really scary in my case was that I actually fitted the pump and belt and had turned the engine over for 30 secs to circulate the fresh oil I had popped in. The only reason I found out about the wrong pump was because I had a tiny weep around the gasket and I removed it to see if there was dirt or some other issue. Took the pump off to find the ends of the impellers slightly shaved! Thank god the impeller was plastic.

Anyway, bottom line is that the pump from the 987/997 series will bolt up nicely, but the impeller is a tiny bit bigger.