A few weeks ago my engine started to sound like a diesel truck. The noise seemed to be coming from the drivers cyl head. I could feel a vibration when I touched the cam cover and distributor cap. I removed the cam cover and dist cap to inspect. Everything looked good, so I towed it to my shop.
Put it on the lift and removed the belly pans. Fellow lister Eturbo924/Eric came along for the diagnosis. When I started the engine his mouth dropped. The noise was louder and I could feel knocking on bottom of oil pan. Was a very stressful moment at first.
The vibration when touching dist cap kept calling me back. I removed cap, rotor and upper timing cover. I was amazed at what I found. The cam bolt was loose, so I tightened it and noise was gone. What happened was the cam hub had cracked and broke in 2 pieces. This caused the bolt to be loose. The rotor screws were holding everything together at that point. I replaced both hubs and reset my cams.
I was lucky, it could have been much worse. Strongly suggest replacing cam hubs if your in there.

 

Those are problematic at best.
You dodged a bullet on that one, it could have broken a cam, bent valves, done all sorts of things.

They were on back order when I built my engine.

 

I hardly recognized that part.

I believe the pt. number is 928 105 459 00 (hub)

Good info. thanks for the post.

 

Hmmmm... I rebuild my engine for nothing? Great save, you have to be on the verge of throwing up before you found that.

 

Paul, are the replacement hubs aluminum? Or steel?

 

Steel

 

But, the originals are AL right? Or are they steel to start?

 

They were steel also. Had they been aluminum it would have shredded filings everywhere. The new hubs are factory Porsche from the dealer. The package had a manufacturer date of 8/2009. I'm hoping the newer hubs have modern technology steel and are stronger than 80's steel.

 

That's a big hunk-o-steel to be broken like that.

 

Im thinking to change mine too when I start my rebuilt.

 

A bunch of them have broken, they will crack at the key way, just like that one did.

 

Zeus,
Put that on eBay and you will probably get $1000 as a piece of art.
Glad you ducked on that one.
Roger

 

IIRC this seems like a not-that-common failure mode. But, the question in my mind is why? With the big bolt properly tightened and with the rotor bolts even and not over-tightened to the point of snapping there shouldn't be a lot of force on that piece. Or IOW, the cam belt shouldn't be dragging the sprocket around via force on that piece and thus the keyway.

Am I missing something?

 

Wow! The rotor screws were holding everything in place Time to buy a lottery ticket?

Dan
'91 928GT S/C 475hp/460lb.ft

 

But break they do, I have only seen two of them broken, but others have reported them breaking, and I know they were torqued to spec.
Harmonics maybe.