What does that look like to you?
#16
Rennlist Member
Thread Starter
#19
Former Sponsor
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.
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.
#21
Nordschleife Master
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.
#22
Rennlist Member
Thread Starter
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...
#23
Nordschleife Master
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...
My crystal ball sees a teardown of the engine, dry iron sleeves, new pistons from JE, and happy motoring.
#24
Archive Gatekeeper
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Rennlist Member
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?
#25
Rennlist Member
Thread Starter
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?
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...
#26
Addict
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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.
Sorry to see this.
#27
Former Sponsor
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...
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.
Last edited by GregBBRD; 07-08-2013 at 08:07 PM.
#28
Rennlist Member
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?
Why mess with other coatings?
Is it because the stock coating only works on cast pistons, not forged?
#29
Former Sponsor
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.
Last edited by GregBBRD; 07-08-2013 at 09:47 PM.
#30
Nordschleife Master
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...
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...
So JE said that the same etching process that is used with stock pistons should be used with their coated pistons?