That's what I use exclusively.

 

The continued problems with this iteration of the 991 GT3 engine makes me think that Porsche is unable to find the problem. Especially if the same type of issues arise in the RS.

It's also odd in how Porsche is addressing the issues.

If it was truly a design "defect" issue you would think the various evolutions of this engine from E to F and maybe G, and especially to the RS, would resolve the issues.

But apparently it hasn't. Which is why maybe Porsche is in some cases simply replacing the top end, which suggests something more akin to a manufacturing "defect" issue in the sense that the factory somehow made a segment of the engine out of spec. But that also doesn't exactly jive, if some F engines are getting the G replacements.

 

I believe that changing the heads does not address the root of the problem. I think that Porsche has analyzed the first batch of engines they have replaced with a G engine and found that the DLC coating shavings did not affect the rest of the engine and most likely got caught in the oil filter. As a result they have concluded that it's faster(since the top end is disassembled anyway for the initial inspection) and more cost effective to replace the top end rather than the entire engine.

 

There is some excellent ideas surfacing in these posts. I'm on the road but in brief what I understand is that at least in some part PAG engineers have identified both the DLC coated finger rockers AND the oiling to be at some point related to the issue hence the revised rocker fingers, oil pump and ECU driven oil pressure in the G and RS engines. Whether an oil analysis would even pick up the DLC coating I do not know other than it may report "foreign body" as in truth the DLC coating as I understand is not from a pure metal family. The revised oil filter on G and RS engines may be a red herring as it would appear these items are not upgraded on rebuilt E & F engines. The ability of the oil to provide a protective layer between the rocker and cam is likely part of the issue as Dundon have eluded. It still remains to be seen if G engine design changes have rectified the issue but you would hope PAG have some confidence in the re designed heads and components they are using for the warranty rebuilds? That said I think there has been a real learning curve here for PAG and it's possible the issue has been alleviated but not completely addressed. Only time will tell I guess...as for better oils - yes there are many with better ZDDP levels and additive but if they are not warranty friendly then another issue persists etc...

 

For those that have an interest on learning more about DLC. I am not an engineer but was able to grasp a bit about the issue. There is a particular section that somewhat covers its use in engines. Good read for a Sunday.

https://en.m.wikipedia.org/wiki/Diamond-like_carbon

 

While we are on the topic of DLC, some you might be interested in this video of a couple of basic tests done on a DLC coated Panerai watch.

You can see that the scalpel and file have no impact on the coating. While the tests are quite basic, it does give some kind of indication of how hard a DLC is.

And I like Panera watches too, so it was of double interest to me

 

Pretty cool video
But yet gt3 motor can wear that coating pretty quickly.

 

Some food for thought. In the section titled Tribology, the Wiki summary indicates that DLC is used to reduce friction during BREAK IN. Given how much discussion we have had in this board about proper break in procedure, whether there is any relationship between wear rates and break in procedure. Could it be that those motors that were aggressively broken in (if at all) have worn down quicker? Is there any relationship? It would be interesting to establish correlation, if any.

Macca - do you have any data on this?

 

Interesting article indeed. So many questions it raises.

The wear we are seeing is almost always occurring cylinder 5-6 worse of all. When the rockers on one bank are layer out the wear typically reduces considerably as it moves towards one end of the bank.

Heat may indeed be a factor (read middle paragraph below of snippet of article). The updated G/RS heads have additional oil lubrication. This may also be in order to reduce heat. It's possible "hot spots" in the heads created by inadequate oil distribution may have accelerated the carburization of the DLC coating contributing to the issue...of course lack of ideal lubrication between cam lobe and DLC rocker finger could be promoting heat transfer.

When you consider how complex and how many variables are needed to be considered for a stable DLC coating In a constantly changing high speed high friction environment such as a 9000 rpm GT3 engine head - the mind boggles as to the multiple potential issues, especially first time being used on a production H6 engine (ie no F1/WEC type production component budgets).

Purely speculation but I suspect PAG have been chasing this issue down for a while trying different versions of DLC rockers earlier in the piece and lubrication enhancements later.

I doubt we will ever hear from the horses mouth one this issue. A shame as it promotes rampant speculation. The good news is that it appears to be an issue that can be addressed through subtle changes in design and perhaps supplier components...

 

I did some research on DLC after this post, and there are few reoccurring themes there - DLC durability can vary tremendously with changes in thickness and structure of coating as well as what material is coated. Some changes have an exponential effect, so even a small change in some of these parameters can change life expectancy by factors like 10x and even 100x. Also, testing of its durability is still not fully standardized, it seems. Not sure if that's what happened here, but it seems possible.

An even less scientific observation - my DLC-coated watch has coating damaged is some spots, and the damage is not from wear of the coating but from metal under the coating being dented, like pressed in, and the coating creasing as the result. Maybe the metal under the DLC coating in GT3 engines is too malleable and allows the coating to deform and lose strength that way.

 

Hey Mark,

A good DLC coating is very good at holding oil and reducing friction. The DLC will only last if there is oil, as the article said, the coatings reduce wear during oil starvation... Every F1 team is using DLC, WEC is using DLC etc. If you can reduce friction in the engine you make more power available to the wheels.

The issue with the followers is if there is no oil film allowed to form then the only lubrication you have is DLC. The coating alone can't lubricate dry and does require oil.

The solution we're designing is a mechanical redesign of some of the valve train components to ensure an oil film is formed consistently, regardless of oil pressure etc... We're also going to provide world class DLC coating from the same source used by F1 and WEC teams (unfortunately not the same place our finger followers were coated...).

Any solution that comes with the 991.2 will be interesting to see. We will be keeping an eye on the parts to see when they're available.

The issue with the wearing of the finger followers isn't the DLC wearing, the DLC is likely not causing much of an issue circulating in the engine, the issue is the metal/metal wear between the cam and finger follower. Any metal that circulates through the engine creates abrasive wear. The amount of time for the ecu to signal a misfire fault due to valve opening deviation (finger follower wear) is likely long enough for the metal to be circulating for some time. The oil filter will only get a % of the metal circulating. So that means the metal circulating will get into all the areas the oil circulates through and issues may not show themselves for quite a while (think bearing wear causing spun rod bearings, scored cylinders, compression/leakdown issues etc...). The issue could show itself many years later, but typically once wear starts, it continues on it's own as the surface finish/oil holding capability is changed...

When we bring the solution to market (in about 7-8 weeks) part of the install be a thorough borescope of the cylinders, a check of the rod bearings for wear etc... to ensure the engine doesn't need anymore while it's open.

We'll have more information and pricing on a few of the options in the next 7-10 days.

As soon as we have parts we'll share what we're up to and why we believe so strongly this solution will work long term.

 

Well done. Assuming this resolves the issue, it boggles the mind how PAG, with all their resources, couldn't have come up with something like it (or better) much sooner.

 

Good stuff, Jamie. Looking forward to learning more.

 

Jamie can we get to these parts for inspection without removing the engine? I want to know now and not wait for the dreaded light. What is involved and how many hours labor to check this out. Thx Ed

 

There's a lot of constraints on an oem when it comes to addressing an issue. IMS bearings, BMW rod bearings of every generation, etc. a lot of times the aftermarket has more latitude to address issues than an oem.

Want to get the data out as soon as possible. This is too great a car to wait for bad things to happen.

Charles has had one of mine out, to take a look at them based on some misfire codes I was getting (paranoia). Let me ping him and see if this is advisable as the correct way to do it is engine out...