Strike two- question on cam deterioration

[RDM]

(excerpted from Start with maintenance, end with disaster. Or opportunity )

So here's the second piece of bad news (after the broken head stud and before the broken ring, in case you're keeping score).





This doesn't seem right for a 60,000 mile engine. What are possible causes?

Obviously a regrind is necessary. Recommendations? 964 grind? Webcam 20/21? Pixelated magic fairy dust?

Anyone have 964 cams or SC cams they'd like to see go to a loving home?

Next question: Given I have two cam lobes that look like this, should I spend the money and time to open the case and see what lurks inside?

[Steve@Rennsport]

Dru,

Unfortunately, I've seen plenty of that.

Causes have been mainly three things:

1) Insufficient ZDDP in engine oil. These engines need 1200ppm of both ZN AND P for protection.

2) Improperly ground rocker arms right from the factory. The rocker pads are not ground parallel with the shaft centerline which leads to more pressure being applied on one side of the lobes than the other. We have to re-grind each and every new rocker arm we get from Porsche as well as ALL used ones during a rebuild.

3) Clogged spraybars that starve a rocker/cam lobe of proper lubrication.

If it were my engine, I would be taking it all apart to clean & inspect everything VERY thoroughly.

Hope this helps you,

[RDM]

Originally Posted by Steve@Rennsport

1) Insufficient ZDDP in engine oil. These engines need 1200ppm of both ZN AND P for protection.

2) Improperly ground rocker arms right from the factory. The rocker pads are not ground parallel with the shaft centerline which leads to more pressure being applied on one side of the lobes than the other. We have to re-grind each and every new rocker arm we get from Porsche as well as ALL used ones during a rebuild.

3) Clogged spraybars that starve a rocker/cam lobe of proper lubrication.

If it were my engine, I would be taking it all apart to clean & inspect everything VERY thoroughly.

Steve,

Thank you for this information. This is very helpful. If it were substandard oil, shouldn't I see more widespread problems, rather than just two cam lobes?

Are there other things inside the case that display unusual wear despite low miles and good oil ( if number 1, above, isn't the problem)?

Pistons measured to 95.00 + 0.04, cylinders 95.00 - 0.03, if that helps.