Porschetech3

I see exactly what you are talking about, Thankx for pointing it out !!

Iceter

Certainly, in those pics you can tell that if the piston in the damaged cylinder was at BDC, the scoring would be visible from above the piston.

Since this phenomenon seems to occur in only 1 or two bores, it is important for the tech doing a PPI to view every bore with that piston at BDC and not assume that everything is fine because he can see good cylinder walls in just a couple of cylinders.

He would have to rotate the crank as he works his way through both banks.

docdrs

Baz, thanks for continuing your postings on this and here on the site. I have reread some of your postings re shrinkage to give me a better grasp of reasoning, cause and prevention, giving me some tools to minimize this from occurring. I enjoy your reasoning and ease of conveyance to the reader......always good to hear your and Jake’s thoughts.

edomund

Baz has been stating his theory pretty early on in this thread that a majority of these engines that have failed has been from shrinkage. He's posted the theory with pics and data to back up his findings. This is very helpful and is a value to owners trying to understand these failures and what to do and look for going forward. What I think is not very useful is posting theories with little to no data to backup the theory and then owners going down rabbit holes chasing "problems" that may or may not exist. For example.

1. LSPI - LSPI theories has everyone ditching their oil (to prevent LSPI) to run the oil mentioned in this thread. No pics or data showing signs of LSPI (correct me if missed that post) and yet everyone is switching oils. Not saying you shouldn't switch out Mobil 1 as it has been shown with UOA to break down faster than other oils, but there are many good oils not just the recommended oil people have been told to switch to in this thread.

2. Fuel injector failure - It was mentioned that the injectors were sent out for testing but then no report back if they were good or not.

Baz has also requested this engine be measured to see if shrinkage occurred and no response was given. If shrinkage is at the root of these failures then for the most part proper warmup seems like the main preventative measure for 9A1 engines. Knowing this would alleviate a lot of guessing, arguing, and people worrying about items that likely don't occur.

okie981

For your item 1, regarding nothing posted about signs of LSPI, go back to the video Jake posted of the teardown of the OP's engine, skip to 4:42 of the video. Rod bearings on the combustion chamber side of the rod big end show quite a bit of wear. If this was a port injected engine with high compression (11:5 or higher) maintained and driven the same way, would it have experienced the same rod bearing wear? I don't know, but LSPI is certainly a suspect.

For your item 2, I too would like to see the results of the fuel injector testing, especially the one from cylinder #1.

Charles Navarro

Here are the results from the failure analysis. Sorry it took me so long to post. I had the raw data but didn't have a chance to compile it for posting as I've been travelling literally non-stop since late Feb.


Initial observations. Cylinder 1 has failed from bore scoring. As the corresponding piston isn't damaged at the gauge point, we were able to measure it at 3.9919". All other pistons measure 4.0149 to 4.01505 which is a normal deviation in diameters on used forged pistons. Piston to cylinder clearance on these engines new are .0007-.0009" with the ferroprint coating being about .0008" thick on diameter (.0004" per side).

Cylinder 1 has .0005" of taper, but is ovaled badly top to bottom on the tight side over .002, which clearly points to the block and bore distorting closest to the main saddles. Interesting enough, cylinder 2 visually is the next worse and it's also starting to get ovaled in the middle, being tightest at that point, not at the bottom of the bore, and none of the other cylinders are tighter by the main saddles. Anywhere the cylinder has become ovaled, reducing clearance, means the coating in the piston is sacrificed to maintain required clearance. Once the coating is removed, you have metal transfer (and scoring) from from sliding of aluminum on aluminum (galling).

It is also interesting that cylinder 3 and 4,5, and 6 have similar taper which is in spec of .0005" and although the bores do get slightly ovaled, it's on the larger side, increasing clearance, not decreasing it.

With regards to surface finish, I find that more interesting than the bore ovality and taper measurements.

To explain why my tech took three sets of measurements, there was a dark band in the bore that had a clearly different wear pattern and resulting surface finishes compared to where the top ring was running and where only the piston skirt travels.



This is not the failed bore, but one of the better ones, so you can see there were some scuffing in the bore indicating other cylinders were going to start to score as well.

For alusil, KS provides reference values for surface finish on a properly prepared bore, in micro-inches:

RpK 14.63
Rk 20.63
RvK 6
Ra 7.88

Depending on finishing procedure, KS recommends a min RpK of 11.25 for the mechanical or chemical exposure process with a max of 26.25.

Typically, as a cylinder is run in, we expect the Ra to drop, as the peaks gets knocked down (reduction in the RpK). Looking at the "L" values which are at the bottom of the bore, that is typically indicative of the original bore surface finish when originally manufactured.

I would fully expect cylinder 2 to fail next as you can see the RpK and RvK have dropped significantly.

The reason why the bore gets smoother before it gets rougher (scoring) is the way a hypereutectic bore wears. The precipitated silicon particles are left behind at the surface after the softer aluminum has been removed. I won't get into the specifics of the required percentage of crystal exposure, particle size, or distribution, but the exposure depths are critical to longevity of the Alusil as oil film pools in the voids between the silicon particles, providing the hydrodynamic lubrication for the piston skirts. So as the bore wears, the silicon particles fracture and fold over into the aluminum, along with compounds deposited by the anti-wear package in the engine oil. This occurs over and over again, but at some point, the distribution of silicon particles is not enough to support the load and maintain the proper oil film, resulting in scoring.

Our next step in development is to look at the lubricants to perhaps find a solution. Mercury Marine's Mercosil is very similar to Alusil, but with the addition of graphite to the matrix as a solid lubricant. Mercosil blocks are known for great wear life and do not score from what information I can find on the internet. Lake Speed, Jake, and I are working on an EP additive that might help slow down the wear, but we do know for a fact that gasoline direct injected engines suffer from fuel dilution among other issues like soot formation, LSPI, and other issues that can be addressed through formulation changes in lubricants. That's the reason why there's a Dexos2 and stop gap API SN+ standards to address LSPI concerns and why we helped develop the DI40 product to do more than just address LSPI.

Lastly, the side of the engine with more distortion in the bore (ovality) also happens to have a deck that is .004" warped, where the other side of the engine is just .002" out, measured on our CMM. I would venture to say the side of the engine with more distortion, warped deck, and scored bore is also the side that runs hotter, if I were to venture a guess. Porsche's use of flow restrictors in the water jacket to slow down coolant flow probably doesn't help matters.

There is more research available on the wear mechanism and lubricant's role in it, as well as the effect of ethanol fuels as well. Unfortunately, my time is limited and I've spent half a day just working on one single post on RL with stacks of SAE and other research papers to help me understand this issue.

The takeaway is you need to use a high saps oil, shorter drain intervals to address fuel dilution, and let the engine get up to temperature before you start hammering on it, as there is little more you can do. I let the car get off fast idle before I drive off, and that's regardless of what car I'm driving.

Charles Navarro

I may be wrong, but I believe Jake mentioned to me that the offending injector was seized in the head and was damaged in the process of being removed, but then again, I am not sure if that is this engine in particular since we have so many engines in queue for Jake.

Balr14

This all sounds like bad engineering, or failure to subject these engines to long term testing before releasing them to the public. I predict a lot of 997.2 engines in your future.

okie981

So let the fast idle subside down to normal idle before driving off? This is about 45 seconds to 1 minute in my 981 car from a cold start. I've seen other posts that say it's recommended to drive away as soon as possible after starting, staying at low RPMs and light load until warmed up, so this could imply to not wait for the fast idle to subside. I think I see your logic, driving away with rich fuel mixture only promotes fuel blow-by into the crankcase oil, but I just want to make sure I understand this clearly.

okie981

I took the online 9A1 rebuild class from Jake week before last, and during the class he mentioned he had to send a 9A1 cylinder head to a specialty shop to have a stuck injector removed using EDM. Don't know if it was the same head.

user 72902

I think you will be ok either way because it’s a short interval. Starting the car, backing it up, closing the garage door, and heading down the drive would take me about 45 seconds. The more important point which we know is not to hammer it until we get them warmed up.

okie981

True, but in my case I can be driving away 10 seconds after starting the car if I press the button to close the garage door as I back away just clear of it and head away in gear as the door is closing checking in my rear view mirror to make sure the door closes. 30 to 45 seconds of rich fuel mixture blowing past the rings can add up over days of use, especially for those who don't have long drives after each cold start. Fortunately, I rarely start my car for short drives, living in DFW will do that for you. Typical drives are a minimum of 25 minutes.

Prairiedawg

Thanks again for following up with us. I'm assuming these results are for the OP's (Bronz) engine? Forgive me if I missed it.

It sounds like your findings are also mirroring Baz's if I'm not mistaken. Would the "shrinkage" affect a rebuild using Nikasil liners also, compressing the cylinder liners inward, or does the machining relieve any potential movement?

Also forgive my ignorance, just trying to understand. If running any engine(DFI, etc) for miles to burn off built up condensation, does it also flash off unburnt fuel in the oil the same way spilled gasoline evaporates quickly on a hot driveway. I would think due to the high volatility of fuel it would evaporate even more quickly than water in the engine. Just curious,I've always wondered that.

Charles Navarro

Yes, this is Bronz's engine.

I don't see the "shrinkage" on any of the other cylinders by the main saddles and in fact, they actually opened up on the other bank. I believe we're seeing the block moving, either as a result of stresses built up from the casting or machining process that are relieved as the engine heat cycles.

Introduction of ovality and taper to the bores as the engine is subjected to repeated heat cycles and wear is similar to what we see with M96 and M97 engines always being significantly out of round. People who rebuild thse engines and don't address the bores likely don't own a bore gauge or profilometer - ignorance is bliss.

As long as the block hasn't been thermally overloaded - loss of coolant, I would expect the bores after they are bored, plated, and honed, to stay round.

We increase the piston to cylinder clearance, even if using OEM pistons, and have the ferroprint coating replaced with a grafal or similar anti-friction skirt coat.

The piston to cylinder clearance is just too tight in my opinion from the factory.

I can't comment on the fuel vaporizing off, but I've seen fuel dilution numbers upwards of 5%, granted driving habits and long drain intervals have a great part in making this problem much worse.

Prairiedawg

Thank's for commenting. How are the blocks moving (direction wise)? So some cylinders are moving inward and some are expanding? Is it possible the block's are twisting somehow, causing the deck height's to change and the cylinders to move? That would explain a few things in my mind, especially if some cylinders are closing and others are expanding. I'm not an engineer by any means, just have a bit of mechanical aptitude and find this stuff a bit fascinating.

5% dilution, yikes!