Cheburator

Nope, the engine has run for a total of 6hrs real engine time... all controlled environment - inside a garage, dyno room and then 2hrs on track...

terry gt

Oil driven detonation broke the rings on my 5.8 L stroker , and scored the bores on the thrust area .

Dutch 928 fan

LOL

GregBBRD

The piston looks normal. Those "pits" in the picture are typical carbon under borescope lighting. The uniform carbon to the edge of the piston would indicate that there is minimal oil in the combustion chamber....and especially very little going past the rings. Looks like the rings have seated very nicely.

Those do appear to be scratches in the cylinder wall....not sure what bore "style" (Alusil/Nicosil) and piston "style" (Stock GTS, aftermarket plated, raw aluminum) you are running, so it is tough to draw any conclusions....but it doesn't look very happy, for 6 hours of running. Scratches in the cylinder walls can come from various sources....debris flying off of deteriorating rod bearings, debris sucked in through the intake, inadequate piston to wall clearance, incompatible bore/piston combination, excessive piston "rock", etc.

Cut open the oil filter and inspect the paper. The oil filter is your "x-ray" picture of what is happening inside the engine.

John Speake

How long was the engine run on trumpets and no air filters ?

ptuomov

The major thrust of 5-8 bank is on the inside, intake side, right? You wouldn't think foreign objects would go only there, they'd naturally fall to the exhaust side.

Wild guess given that it's all on the side that gets the highest load: Piston material friction welding to the bore material, then breaking off on one side, and scoring both. Like running aluminum piston on an aluminum bore. Maybe the piston coating wore off and exposed the aluminum on aluminum? Seeing the piston skirt would be interesting. This just a wild guess.

Cheburator

I think Greg and Tuomo may have it. Pistons are JE with Tuff Coat on their skirts. I have it in writing from JE that they will work in Alusil. Pistons to bore tolerances were within the spec given by JE when checked by the other Alex (engine builder) prior to assembly. Educated guess the bores were not prepped properly...

ptuomov

What's the "proper prep" for those coated pistons?

My crystal ball sees a teardown of the engine, dry iron sleeves, new pistons from JE, and happy motoring.

Rob Edwards

Naive question: Is nikasiling a block not an option (due to availability or cost?) in Great Britain? For all the stories, archived and new, of issues with piston coatings and Alusil compatibility, I'm not sure I understand why not Nikasil? My cost for boring and Nikasiling was $1600, three years ago. Maybe it's more across the pond?

Cheburator

Not really an option in the UK. Not a single company, including Capricorn who work with F1 teams and in the past saved a few GTS blocks with stupid oil consumption issues are willinb to nikasil a whole block. Capricorn tood me I could have nikasiled liners made, but firstly they are expensive and secondly, they are more expensive than your block...

The proper prep is to expose the silica crystals just enough so they trap oil, but not too much that the are scraped away by the rings. I think your crystal ball is very good, btw...

About 30 mins in a sterile environment - a garage with no load applied to it whatsoever and then a dyno room trying various iterations of trumpet/filter combos. Both places are super clean, with the dyno place - you could eat your dinner off the ceramic floor tiles and the sound proofed walls... So no way the engine ingested anything...

Dennis K

Oh no! Are these the JE pistons that they coated & said would work on Alusil? So Mahle can't do it right & now neither can JE? *sigh*

Sorry to see this.

GregBBRD

I've had virtually ever piston maker known make this claim.....including Mahle.....and have yet to have a single one of these engines run more than a few hours, until the piston coating falls off and ruins the bores.

Fortunately, not all of these engines were designed and built by me....most were from multiple other builders that thought they were the "current 928 engine expert" and I've just been the guy that was handed the "mess" and asked to fix it. I've seen enough coatings fail that if they were all mine....I'd have long ago gone broke and not be in business.

Of course, it's never the piston maker's fault....it's always something else....and they never "stand up" and pay for the engine....even Mahle declined to pay for the damage...or even replace the pistons. You could "flake" the coating off of the Mahle pistons, with your fingernail!!!!

Wasn't anything they did wrong!!!! Not their problem!!!

I'm so sick of it, that I simply will not bother attempting to build an engine with coated pistons and Alusil bores....regardless of who is paying the bill and what they "insist" I do. I don't care who tells me it is going to work. I don't care what piece of paper they give me telling me it works. I don't care how many 944 engines it is working "perfectly" in. I'd rather decline the job than "go down this road", in a 928 engine, at this point in time.

I went "down" the dry steel sleeve "road" when I was doing 951 race engines by the handfuls. This required a lot of research and a lot of "failed" engines to get the process correct. Piston clearance was a huge issue....I "stuck" more than a couple of those things, figuring this out. The fact that they were turbocharged and added a lot of heat into the equation made the process even more difficult.....a 928 application might be easier. However.....

I've had the Nicosil coating work perfectly (100% success ratio.) Done this dozens of times, now. I've got the piston clearances figured out, got the rings figured out, and even have coatings that work great in the Nicosil. I've done race engines with Nicosil, I've done street engines with Nicosil. I've had them apart at 10 hours and I've had them apart at 50,000 miles. Never had to have one redone....never had to "retire one" (well, never from any issue with the Nicosil.)

There are some small "tricks" to making it work..."tricks" that need to be done after the block has been coated and things that need to be done before it is coated. It is certainly not the "cheapest" way to build an engine.

As for your problem, cut open the oil filter. If the filter has "chunks" of piston coating inside...you know the next step.

BTW....I've recently started trying to keep already "done" Nicosiled 928 blocks in stock....since the lead time to have a block Nicosil coated and then perform the "magic" to make the block "live" takes months. Just sold the last one I had...but I've got a couple more that are due to be back here, from coating, soon.

LT Texan

Why don't they just replicate the tin plating (?) on oversized pistons?

Why mess with other coatings?

Is it because the stock coating only works on cast pistons, not forged?

GregBBRD

Both Mahle and KS guard this process like it is the Holy Grail. According to Mahle in the US, Mahle in Europe apparently will not even share the secret with Mahle in the US.....which is why they use their infamous "Ferroprint"....that I had partially fall off of a set of pistons....the balance of which one can blow off with an air nozzle.

Not only that, but the whole "Alusil" thing is pretty damn fragile....which is why Porsche has never used an Alusil cylinder (they did try them in the very early 944GTR engines) in a race engine. You rub a particle of dirt down an Alusil bore and you have a scratch.....

There's also a "rumor" that the silicon isn't as uniformly mixed in the aluminum (as one might be lead to believe) and tended to migrate towards the surface as it cooled, making the quantity of silicon, once the cylinder is bored way oversize an unknown.

And finally, it is exceptionally difficult to determine how much and how well the silicon is exposed after boring and honing. One has little alternative but to "trust" that it was done correctly.

Other than those few things, no reason.

ptuomov

Someone should make aluminum dry sleeves for these engines with Nikasil/Nicom plating. With interference fit they would probably be about as strong and about as heat conductive as the original cylinder tower. The big difference between plating the block vs. installing plated dry sleeves is that the plated dry sleeves can be shipped at a reasonable cost.

So JE said that the same etching process that is used with stock pistons should be used with their coated pistons?