SleepRM3

Ken - I have selective reading comprehension

tonypai

My story is almost exactly like Ernie's. 96 Carrera with 99K miles. Started the rebuild in April, thought it'd be a quick 2 month process. LOL.

The car had a top end rebuild 15 years ago at 40K miles by the PO at the "Porsche" dealership in New Orleans. They outsourced the job and per Steve Weiner "worst valve job I've ever seen, every valve was bent and none were shimmed."

I'm in the final stages of putting everything back together and hope to get it back into the car soon. Last minute decision to rebuild the fuel hoses and I sent them out to get replaced.

Edward

Nice to see yet another one!

Mine is likewise a DD, been so since 2001, and for those first 3-4 years of my ownership it also saw regular track duty. Still a DD and now at ~150K miles, she uses 1qt per ~2500 miles (probably "uses" less as I have that annoying little dribble from the cam-chain housing that just wets the garage floor, but no puddle), and still drives superbly crisp with a "connected" and interactive feel that few cars can approach.

How can you not love a car that is so rock-solid dependable and delivers "supercar" performance(from another era ) and drop-dead-gorgeous looks?!!!

Edward

JPS

I've had 2. 1 had 103k, one had 132k. Neither had rebuilds. Current is only 60k, so hoping I don't have to consider for some time.

earossi

Thanks for the response. You pose a valid point. Had I not wanted to get into my engine using the excuse of oil leaks and plugged SAI ports, I believe that I might have elected to continue to drive the car. It showed no evidence of oil consumption, and the engine pulled hard and ran flawlessly.

But, I did pull the motor to do a valve job. And, in the process of disassembly began to find things that drove me deeper into the motor. The first was spalling on one camshaft lobe (picture attached). Steve Weiner opined that he was beginning to see a lot of this and surmised that it was due to the change in oil formulations (lowered ZDDP levels) several years prior to my finding.

The cam damage finding caused me to probe deeper into the motor looking for any similar or collateral damage. When I pulled the #2 cylinder, I discovered a ring land failure on the piston, indicative, perhaps, of some knocking in the engine's life?

So, I went deeper to inspect bearings. And, as noted in my original posting, found all bearings (with the exception of the IMS) to be "perfect". No damage or perceptible wear at 107,000 miles.

In summary, the OP is correct in that with the exception of the two findings, there is no reason my motor could have not gone on for 200K+ miles. But, it is speculation how long I could have gone on before further camshaft damage or degradation of the #2 piston ring land would have forced an engine disassembly.

myflat6

New 993 owner chiming in - forgive me for not being as knowledgeable yet on this car. I have a 'bullet proof' 3.0 in my 911SC that has not given me any issues in almost 15 years of ownership. I have used Mobil 1 for the life of the car until last year when I switched to Brad Penn.

It seems as though there is no consistent link to the 993 having early valve guide wear. The two possible links that I have read about are: 1) Engine cover creating excessive heat 1B) Possibly related to the prior - hot climates and 2) Reduced ZDDP levels. I was going to add a third, which would be poor engineering/design, but it seems that the top-end wear/rebuilds are all over the map in terms of mileage. Are the same guides used when the top end is rebuilt, or are there improved guides now?

I would like to try to use the available data from this community to help us confirm the above. Maybe we can develop a poll or some method for gathering data points for analysis?

Here are some questions I would have:

1) When did the ZDDP levels become critically low? I ask because there have been several examples of top end rebuilds 10-15 years ago. This might partially de-bunk this as being the primary culprit. UPDATE: I did some more digging and it does appear that changes began around 1996. So, the timing plays into this as a possible culprit for sure.
2) Has the forum witnessed as many rebuilds in Europe? This might help us dig deeper into climate or emissions control differences being potential culprits.
3) Here is one curiosity for me. I am wondering if the new service intervals recommended by Porsche with the 993 could be the primary reason, or at least exacerbated the issue of worn valve guides. 15,000 mile service intervals during a time where ZDDP levels were dropping would certainly be cause for concern. When I was shopping for my 993, I looked at several cars that were serviced as per the service manual at 15,000 miles. Many of these cars were serviced by the dealer as they were prior lease vehicles. Seems like this could be an issue during the early life of the engine during break-in, etc as well.

Maybe there is more in the forum on this topic already - I apologize if that is the case. Maybe this is too large a task to try to solve, but I am very interested in this - especially since I am now an owner of a 993!

mac993

Mid 120's on mine. No top-end rebuild done and just passed smog last month. Have had CEL's in the past but only from battery disconnect then the drive cycle clears them up (once I was patient and learned how to do it). Small oil drip but never any puddles or anything of the like. Truthfull outside of my Ridgleline it's the most dependable car I've ever owned. And considering I've owned it for the last 14 yrs that's saying something!

race911

Yes, all factory air cooled 911 guides are crap. Since the first one that rolled off the line 50 years ago. Thing was, before the '84 pressure fed tensioner (and realistically the '80-'83 update idler arm, but still sealed hydraulic tensioner) you'd hardly get a car going past 30-40K miles that didn't puke a tensioner, thus needing a top end.

Enter aftermarket guides. Lukes & Shorman out of Berkeley was probably the originator of the phosphorus bronze guide, and it was internationally used starting in the early '70s. Once those, or equivalent, are installed when the heads are rebuilt you're good to go. Nearly indefinitely.

earossi

I'm not certain that there is a correlation between ZDDP levels and valve guide wear. Rapid valve guide wear has been known for 911's for many years, pre-dating when ZDDP levels were dropped in oil formulations. Porsche has always subscribed to the use of soft valve guides for the 911.

Where I think there is a correlation with the drop in ZDDP levels, is in the mounting incidence of cam shaft failures, such as the one I encountered. This type of failure occurs where there are very high loading of rotating components, such as in the case of the rockers that ride on each cam lobe. My failure appears to have occurred right where the greatest contact force would have been expected between the rocker and the cam: at the maximum diameter of the lobe. And, the loading may have been exacerbated by the non-parallelization of the rockers to the cams (i.e. the rockers are riding slightly cocked on the cam lobes). There is a lot written about this manufacturing flaw on Porsche rockers. And, for a rebuild, it is recommended that you have the rockers reconditioned and then machined to run flat against the cams. Steve Weiner did this for my rockers.

When I first found the failure, I became concerned that oil cleanliness may have played a part in producing the cam failure. That is one of the reasons I went deeper into the engine in order to examine the main and rod bearings. But, I found those bearings to be absolutely perfect.....with probably an additional 100k+ miles of life left in them. In other words, the records showing religious oil changes were supported by what I saw on the bearings. That infers that the lubrication failure mode was related to something other than oil quality or cleanliness.

I am not certain on the date when ZDDP levels were lowered in oil formulations, but I believe it was back in the 2006-2008 time frame. And, according to folks I discussed my failure with, I got comments that they were beginning to see a lot of similar type failures on engines.

As far as oil change frequencies, the extended time between changes that were specified for the 993, are probably not related to my failure, since dirty oil or oil with a depleted additive package don't seem to fit with what I saw. If oil change intervals were too long, I would have expected to see wear on my bearings (which I did not see).

But, even though Porsche specified a lengthened time between oil changes, most of us who have owned Porsches over the years, change oil much more frequently. In my particular case, I have my car on an oil change frequency of once a year, or every 5000 miles, whichever comes first.

ilko

Just a quick follow up... When I sold my old 993, it had 111K miles on it. It was using a quart of oil every 2K miles.

This "new" one I've owned for almost 18 months. I changed the oil a few months after I got it, in November of 2013, with Brad-Penn 20W-50. And have driven the car exactly 3,000 miles since. The other day I drove to Baltimore and on the way back I noticed that the oil level gauge was almost at the "low" level. So I added a quart. In other words I've put 3K miles on the car and it used only one quart of oil. On an engine that just turned 112,000 miles. Not bad I think.

911-TOUR

107K here, barley uses any oil.

almostold

121000 MILES. ORIGINAL OWNER 1995 C2. CHANGE OIL EVERY 5000 MILES OR ONCE A YEAR.{BRAD PENN 20-50) TPC SUPERCHARGER AND INTERCOOLER INSTALLED AT 70000 MILES. 1 QT. EVERY 5000 MILES.
NO TOP-END OR INTERNAL WORK. CAR RUNS GREAT , RECENT DYNO RESULTS 341HP .

cluskera

110k miles no issues . Doesn't use much oil. Leak down showed 3 / 4 % . Interested to hear oil recommendations .

993Porsche

228K now and no rebuild.


Ken