Don Terrill’s Speed-Talk

Hi, I just received these pics from a friend with a turbo Nissan engine and was curious to understand what is happening here.
Leak test was ok, around 11% in all the cylinders, but something is definitely not ok, as pistons and chambers are equally black and cylinders are scratched and dark blue
Is that bore wash and overheat?
PS: it has water injection and 6000 miles

Looks like it got too hot.

More details needed.......boost, power etc.


Stock pistons?
Piston skirts?
How much knock?
What fuel?


If the water injection was working properly, there wouldn't be all that carbon / oil deposits.

Looks like the Pistons are getting knocked Round and the rings are unseating .

Looks odd, but i don't think the color it means anything in particular.
Your burn weird fuels, it makes weird deposits. Every color of the rainbow is possible

The bores being scored might mean something.

Unfortunately I just know it runs on pump gas, no knock in ecu logs and that ptb is 0.0035" (3.386" bore)

Were the pistons shotpeened or otherwise blasted because it looks to me as though the scratches go the full length of the piston travel as if there is foreign particles imbedded in the skirts. The ring belt part of the bore at the top doesn't all that bad but I would bet that he's not getting 11% at mid stroke with those scratches.

Yep, those scratches are consistent with dirt contamination. Could be ingested (air intake) could be debris when assembled.

Note: overheating will cause scuffing on four corners of the pistons and leave marks there on the cyl walls.

Scratches originating above the ring pack line and continuing down the bore is air filtration contamination ,scratching or scoring below the oil ring line is oil contamination,the pictures show both but the scoring below the ring line is a lot worse than above ,the blueing of the bores in the product i work on is definitely over heating . The carbon on the valve relief side of the piston crown is oil washed . I take it the major thrust face is opposite the valve relief side of the piston?
Strip and inspect looks to be the next step, cheapest way out.

Matt80 wrote:Unfortunately I just know it runs on pump gas, no knock in ecu logs and that ptb is 0.0035" (3.386" bore)

Some pump gas has blue dye, oil can have dye, and windshield washer fluid has blue dye.

The guys might be correct that the scratches are from some kind of dirt contamination. Happens a lot.
We all know engines need to be "clean", but It's no simple matter to master that.

hoodeng wrote:Scratches originating above the ring pack line and continuing down the bore is air filtration contamination ,scratching or scoring below the oil ring line is oil contamination,the pictures show both but the scoring below the ring line is a lot worse than above ,the blueing of the bores in the product i work on is definitely over heating . The carbon on the valve relief side of the piston crown is oil washed . I take it the major thrust face is opposite the valve relief side of the piston?
Strip and inspect looks to be the next step, cheapest way out.

Yes thanks, I'll strip and inspect asap. But I also need to start a new thread about bore wear

About the dirt under the oil rings, he has an Accusump. Always worried for any dirt there.
Is there any filter for it?

Other pics:

I finally received the block in my hands: what do you think of these scratches?

Picture looks like the top of that piston has seen some detonation. Is it a trick of the light and camera, or does it look like it has been sandblasted? Detonation looks a lot like cavitation burn on a propeller.

modok wrote:
We all know engines need to be "clean", but It's no simple matter to master that.

I see enough turbo engines running with nothing more than a screen over the compressor inlet to keep the birds out, that it may not be a simple matter to master "clean" but attempting it in the first place would be one hell of a start.