I would suspect the heat cool cycle is a bigger issue. The crack propagation from a key way corner is VERY common on all metal assemblies. It is why woodruff keys don't do this as frequently even though they remove considerably more material than a square key. The line is circular and much less prone to crack.



Materials 101 sharp corners and ragged machining are fertile grounds for crack propagation.

 

I have seen cam snouts get a bulge in them from overtorquing the sprocket bolt. That could put a shearing force on that hub. I have had one of those hubs break on a car I had years ago when I tried to remove it. I found the bulge when I tried to fit the new hub over the cam snout.

-Joel.

 

That would be a "Oh Chit" moment.

 

No doubt at all that they do break. I for one am interested in why.

Agreed. If it's going to break, it will break at the keyway.

Interesting.

I'd like to know the N reasons they break. That way if I discover one of N reasons when I take something apart I know that the hub should be replaced.

One thing I have noticed during sprocket replacement is that the 'ears' of the hub deform when you fit the temporary bolts. Or, more specifically, they deform when you loosen the sprocket bolt.

I am thinking that over-torquing - or very unevenly torquing - the rotor bolts could also accelerate breakage.

 

Great save Paul.

Another item for the maintenance check list.

 

Have the hubs magnafluxed for cracks. It will show subsurface cracks.

 

This was a good save, but you did not have to hear the worry in his voice. Paul was waiting for his garage to have a free space so he could work on his car.
This was worse than a birth waiting to find out what was wrong, it sounded like a loose rod and this went on for a week. I gained several white hairs during this stressful diagnosis while speaking with Paul, I kept the optimistic outlook and said it was something minor . Let's hope his wipers don't break I can't take the stress .

 

Interesting... I have the Porken adapters to fit HTD sprockets on a 16v and provide adjustability, but have been waiting until the sprockets need changing. The hubs are shaved down from the original dimensions. I'm thinking that I should get them magnafluxed now, well before I actually need them.

 

no doubt!!

 

Yeah it was a terrible sound. We had the car up on the lift and were able to hear the sound clear down through the oil pan! I thought for sure he was P-cked. I was trying not to show it since I had hoped we could isolate a bad roller or some thing... but as soon as I heard it I was shocked. I think he read my surprise... guess that is why I am no good at poker.

I did also feel the cap and could feel the rapping there. Then when Paul removed the cap and rotor we could see that the paint for the bolt location was chipped and missing... well more accurately it was in multiple locations. He actually said... hmmm... this is weird and put his finger on the bolt to touch the paint... and the bolt moved! You could see a light bulb go off in his heard and the fears just melt from his heart.

He was so happy he jumped and ... gave me a hug. Now... Paul is a real sweet guy... and if I were "that way" I would be flattered but hey... he was happy so I let it go... Bahahahaha

Sorry Paul it was a funny moment... had to share! :-)

Anyway figured I would put in my 2 cents. It was a sound none of you would want to hear... and I hope no others do. But if you do... make sure you remember Paul and this post. He dodged a bullet and hopefully his experience will help others do the same.

Eric
Eturbo924

 

Some people are smart and some are lucky.
It sounds like Paul is both.

 

Paul and I have been friends for two years sharing phone calls weekly. We have never meet but he plans on coming to Florida this year so I'm glad you warned everyone of the hugs. He is a very devout 928 nut as Bill Clinton said I can feel your pain. "I'll make sure there are no blue dresses hanging around when he visits."

 

He is very smart and yes this was luck for many of us. He said he was lucky to me... but I say he was smart more than lucky.

Had it been some of us we might have turned the radio up and drove it home. He was smart that when he heard the sound he knew enough that it was bad and shut her down.

He then towed it to his shop. We only started it enough at the shop to listen for a minute and then shut it down to discuss what we heard. Then started and listened and felt and shut it down.

He is very good at diagnostics... not to even talk about repairs! He does things from memory that I would take hours just to read!

All that said he also is a great guy and anyone would be lucky to call him a friend. I feel blessed that I met him. My wife and kids think he is great too! That is more than enough for me :-).

Plus he was even willing to take out my sister in law! Now that shows me he has guts as well! LOL

 

Paul...........whats the history on this car especially re. the cam gear/timing etc?

I only ask as I've been playing with cam timing every since owning the fantastic PTiming tool and have had the rotor/cam gears loosend and tightend probably more than most.

Be interested in Kens comments.

 

I replaced the tbelt,wp and rollers 24k miles ago. The cam gears had never been removed. The factory marking paint was intact at that time. Unless someone marked the gears prior(which I doubt), gears have been on since new.The flecks of paint was a clear indicator in diagnosis. The noise just came in without warning. If you do a search for cracked cam hubs you will see that this has been brought up before. Mine was the extreme failure of hub.
I believe that the hubs had cracked at some point in time. The pressure of the bolt then pressed the gear inward, completely splitting the hub.