I was replacing the lower valve cover gaskets today, and after a pulled the first cover (driver's side), I saw this. The tip of one of the cam lobes is pitted for some reason. I went ahead and removed the rocker arm and the mating surface looks fine.

What would have caused this? Overheating? It doesn't have a smeared look like I have seen on engine parts after too low oil. Could moisture in the case have caused some corosion while sitting? Since the mating rocker surface looks ok, is it ok to run this way a bit longer, or does it need a teardown ASAP..... Thanks, Aaron

 

pitting like this may be an indication that at least one port on your camshaft spraybar is plugged. Best to not drive it and get it looked at.

 

IMHO, this is not a spraybar issue (although its not to say that its not clogged), but from what I've seen, this is related to the lack of sufficient ZDDP in the oils that people use.

This is a complex issue that was discussed in detail both on the 911 Forum of Rennlist and the 911 Forum on Pelican.

The cam requires repair or replacement as well as the rocker arm. I would strongly advise that both cams be thoroughly examined as well as all 12 rocker arms.

 

Hi Steve -- do you notice these issues (or at least some trending) in cars with uprated valve springs?

 

I remember seeing this issue in a recent post, I think on the 993 board too. The problem seemed to be related to letting the car sit for too long and moisture eventually causing corrosion; as I recall not changing the oil frequently enough was part of it. I'm pretty sure Steve had participated in that thread as well.

 

Ah, just need to search for "pitting":

https://rennlist.com/forums/showthre...hlight=pitting

For more info, my car has 75K miles and I've been changing Mobil 1 0-40 every 7500 miles. I've only had the car a year and a half, and it was previously serviced by the dealer at 15K intervals from what I can tell. It sounds like more frequent changes are needed in the future to midigate this kind of thing.

Steve, what oil and/or additives do you recomend to keep this from being an issue?

 

Not really, at least with the valve springs we use (Aase).

I do see this in engines with American hard-welded cams and old rockers. I have no issues with having cams welded & reground, but one must use new rockers.

The (lack of) ZDDP issue is a biggie and as all these engines accumulate miles, I think we'll be seeing more of this based on what I've witnessed to date. I do not think its related to letting these cars sit unless one was using an oil that had insufficient corrosion protection. I've stored cars for many years with any sort of camshaft-rocker problems.

 

I would offer that IMHO, the 15K oil change recommendations as provided by Porsche are simply absurd and perhaps good for their business.

I don't think anyone saves money by leaving the oil in the engine for that long and I think these extended oil drain intervals contributes to hydraulic lifter issues as well.

 

Good post, thx for all your feedback Steve.
ps. still too lazy to remove my front seat... yet!

 

I have seen a number of 964 and 993 camshafts that have this pitting compared to older engines and seems to be an issue with the 3.6l engines. I do have a pair of stock 993 camshafts out of my 20k mile core engine I used for my racecar if you are interested in them.

 

Its an issue with all 911 air-cooled engines and not confined to the bigger ones.

 

You have a PM.

 

Steve W

It's intresting to me that the pitting in post # 6 link is on the base circle, not on the tip of the lobe. At the base circle there should be the least amount of friction due to loading (or lack of). The pics posted here by here as well do not seem to be at the very tip of the lobe, where I would expect to see the highest temperature, i.e. hghest loading. Would this not indicate that there is a potential material problem, either compatibility or even manufacturing defect?

I wonder whether this problem is also seen in motor sport applications?

 

It's was hard to get a good shot of the cam, though it doesn't look like it in the pic, it is the tip of the lobe that has the pitting. I should have taken another pic after I had the rocker off to show it better.

 

ZDDP--one more factor in favor of heavy duty diesel truck oil.