Carl Fausett

Let me take a moment to clarify. We do not sleeve the bores. We repair the cylinders. The process is this: we inspect the galling in the block when it arrives and measure how deep the gouges are to determine how far we will have to bore the block to get to a smooth cylinder wall. Then we design and order replacement pistons to match the motor at the new diameter. These are made from forgings and will have the correct piston crown for the particular engine. When the pistons arrive, the block is bored to match the diameter of the new pistons. Then the block is Nikasil plated for toughness, then finish honed to spec. We provide the repaired block, the forged pistons, and a new set of Nikasil-compatible piston rings to the customer.

Again, at no time in this process is the block sleeved.

Petza914

Carl, just curious....with this process, since you're changing the bore size, but leaving the stroke of the motor the same, does it change the engine characteristics at all (move the powerband, increase power or torque, etc) or is the amount of the change so miniscule, that it isn't even noticeable? If it is, what does the volume of the motor move up to and are there options to increase displacement during the process if someone wanted to?

Carl Fausett

Customers report more bottom-end torque, which is what we would expect with a larger bore. If we take the Cayenne S (2007-10) for example, it has a 93.0mm X 83.0mm bore and stroke giving it a displacement of 4.51 Liters. Usually, boring out the cylinder by .020" (.51mm) will be enough to remove the gouging, so if I use that as my example, the bore and stroke will now be 93.5mm X 83.0mm or 4.56 Liters.

So you see, the increase in displacement is slight. I have no doubt that the increase in bottom end torque that the owners feel is because the previous losses caused by blow-by and bad ring seal have been stopped. This is a significant gain in HP, and of course, a great reduction in oil consumption.

The repair is permanent. We have attacked the cylinder wall gouging problem from 3 directions: 1) we have changed the alloy of the piston from a relatively soft casting to a much harder forging; 2) we have changed the cylinder wall coating from alusil to nikasil which has a much tougher and more scratch-resistant surface; and 3) we have changed the piston to cylinder wall clearance, reducing the piston rocking action that (combined with the soft alloys involved) caused the galling in the first place.

Petza914

That's excellent Carl. Thanks for the explanation.

What do you attribute the piston rocking action to - is it engine design, connecting rod angle off the crankshaft, wrist pin position in the piston skirt, or something else, and from your post mortems on the motors you've taken apart, what component do you think wears to the point that allows the rocking to reach an angle where the scoring is caused. Is the scoring caused by piston skirt contact with the cylinder walls or by the piston not running true enough where it gets cocked, binds, and then scratches. The rocking piston explanation seems to make a lot of sense as to why these engines don't score until 50-90,000 miles and it being more than just a manufacturing tolerance issue.

Carl Fausett

...in the shop... lot's to do... I will answer this later. My answer will include a discussion of stacked tolerances and material expansion/contraction at temp. Gotta get in the shop for now... TTY soon.

J'sWorld

The Factory pistons/pins are offset. From what I understand the offset was installed backwards on one bank because the didn't make right and left pistons. I think Jake Raby has the details on this. On my engine we got rid of the offset all together. This is common practice on more race oriented engines.

If you changed the bore size too much it would most definitely affect the VE tables in the ecu. My tuner tells me that they are terribly written to begin with. At which point this becomes an issue I have no idea but It could be adjusted for.

For Carl-
I thought that if the gouging wasn't too deep that the nichrome could be built up to fill those and then bored & honed back to stock size. Is that correct?

For Jake-
From what I understand there are several option you offer in both Alusil sleeves or a plating technique but that you don't do ductile iron/steel sleeves?

slavie

If you want more details on how to "hone" these blocks, you can't do much better than this Sonnen article "Honing Options for Hypereutectic Aluminum Cylinder Bores":
https://www.sunnen.com/NewsDetails.aspx?NewsID=11

Still think you can refinish this yourself?

Also, I know that people on here love to hate Porsche for these engine failures, but all German automakers have had their fair share of issues with these types of blocks. BMW had major Nikasil issues in 90's V8 engines, MB is far from saint, VW W12 engines score cylinders just the same. A lot of it has been attributed to lower quality higher-sulfur fuels, I've even heard that VW released a bulletin stating so, though I'm not able to find it. Apparently EU has better fuels than the US, though Russia beats everyone hands down with super crappy fuels that swiftly destroy any alu-whatever block and scored Cayenne blocks there are far more common.

andrewjt19

Carl,
Thanks for the better explanation of the process. Honestly, I'm a novice and do not know hardily anything about motors. I love learning from those who do. Do you work independently or with LN/ 928 Motorsports? Thanks.

Carl Fausett

The limit to fill a scratch with the NiCom plating is about .003" A mere scratch. These Cayenne gouges are way way beyond that.

We do not work with anybody else. We developed our own process and cure for the Cayenne.

andrewjt19

PM sent. Thanks

Petza914

Carl is 928 Motorsports.

He did the mechanical build (I made it pretty) on my 928 Spyder including the supercharger setup, brake upgrade to Big Blacks from the GTS models (that everyone else said couldn't be done), and engineered the kit (for lack of a better term, but it's way more than that) to be able to run the 6-speed transmission and torque tube from a Z06 Corvette in a 928 for better shifting and ratios. Oh, by the way, he holds the land speed record for a 928 at Bonneville.

andrewjt19

Wow. Nice work and beautiful car. Thanks.

Carl Fausett

J's World: I see your explanation of the "why this happens" in post 21 above. I have heard that theory too, but it doesn't explain to me why the galling occurs on both banks of the engine. If wrist pin offset was the culprit alone, one bank would be fine while the other is ruined. Unfortunately that isn't what we find inside these motors.

My own thoughts:

1) Stacked tolerances: this is engineering lingo for parts that are, by themselves, within spec, but when assembled, combine to be out-of-spec. In this example, say the piston maker (Mahle) was given a spec of 92.8 mm plus or minus .02 mm. That means their pistons could be anywhere from 92.78 mm to 92.82 mm and still meet Porsche spec. The cylinder machinists were given specs too, and it would have been something like 93.0 mm plus or minus .02 mm. Meaning the bores could range from a tight size of 92.98 mm to a big 93.02 mm and still meet spec. Now, if you get a set of pistons from the small side of what is tolerable, and cylinder bores from the large side of whats tolerable, your stacked tolerances may be too great - causing piston rocking that lead to the galling. Stacked tolerances are a very real thing. However it is worth noting that whether or not they explain the "why some engines have galling and some others do not" is just a theory.

2) Material expansion/contraction at temp: another theory that seems to have some merit. Does not work all the time, but I have not yet found a theory that does. It seems that Cayenne's that undergo the greatest chill seem to be the ones most commonly galling. The theory is that the aluminum piston contracts in the cold of a Minnesota or Canadian winters' night, and when the engine is started, the little puck of aluminum is prone to rattling around until it gets a little heat and expands. Once the galling has begun, it is self-perpetuating. I have had this theory shot at by others who said they have a cold country Cayenne that's just fine, but in each case found that they either garaged their 957 at night, or plugged it in if left outside - so it never went from stone cold to damn hot like the others do. Piston knock within a cold motor is a real thing, and excessive piston slap when cold is very damaging. But, whether this is the cause or not is just a theory.

However, it is a theory that we have acted upon and it has gone away - suggesting this theory has merit. The pistons we make for the Cayenne are forged and expand less. As a result, we are able to more closely hold the gap between the piston and the cylinder wall. The piston slap when cold does not occur, and there is no galling.

Still doesn't explain the occasional Cayenne from a warm climate that experiences galling tho. For that I only have theory #1,

Just my thoughts...

andrewjt19

It makes a lot of sense. It might even be a combination of both to a certain degree. My CTT was in fact in a cold climate which I think it part of the reason why it had the galling. I am glad you guys know what you're doing and how to resolve the issue. Hopefully soon I'll be in contact to get my block refinished. Thanks very much for all of the information.

deilenberger

Carl, do you know what happened in 2009 that changed the failures? I've run a survey here on the failures https://rennlist.com/forums/cayenne-...03-2010-a.html - and so far it seems that no engines newer than early 2009 have been blessed with scoring. There is a similar survey being run in the 958 subforum - and no failures have been reported. There is some indication that late in 2008 or early in 2009 Porsche changed the engine block manufacturer - where formerly there had been two, it was now down to one - and that one used a different polishing technique during final finishing to expose the silicon grains in the bores. Somewhere in that hugely long thread on bore scoring are some details on that - including a note on how rings and piston part numbers were specified by who manufactured the block. Here is a direct link to some of that info: https://rennlist.com/forums/cayenne-...l#post15356866

And a direct link to the survey results: https://docs.google.com/forms/d/e/1F.../viewanalytics

Note - there is no claim that the survey results are accurate or definitive - they likely reflect some bias that naturally happens in Internet polls - people with problems tend to be noisier than people without problems - so the percentage of failures may well be overstated. That said - the rest of the info collected shouldn't be biased - and may be of some use to someone.