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Tb48 turbo engine - cylinder scratches seen using endoscope

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Hi everyone!

Could you please have a look at a few photos taken while doing an endoscope check? That's a TB48 built a few months ago, done only ~3k miles with just a few pulls, daily driven most of the time. The engine was definitely not overheated as I drove the car from day 1 after engine rebuild. Stock block, ROSS pistons, stroked 108mm. The block was bored according to ROSS specs (as I was told, but I didn't see the measurements with my eyes, so I don't know exactly what was P2W clearance etc.), bore size is 3,9370, net dia 3,9325.

No leak test was done, pressure test showed 150psi in each cylinder. I believe it burns oil, but I can't understand how much exactly, probably some oil is gone though the vent (catch can vented to atmosphere), my current estimation is ~0.5L oil / 1k miles. 98% of the time only pump gas is used, ~17psi boost. Dual fuel (pump gas/methanol, 12 injectors installed) and 26psi boost was used only on a dyno while tuning and a few street pulls, so engine is barely revved above 4k rpm. Oil pressure has been always 40psi+ in any conditions, normally 60+ while cruising.

When I got these photos using an endoscope, I talked to the engine builder first and was told that it's a normal condition of TB48 with forged internals and 25psi+ of boost. But I'm still concerned about a few details I see: I can see almost no hone in all 6 cylinders in these areas, some cylinders have "clean" piston edges (e.g. cylinder 3), could it be due to oil coming through the rings? I'm also worried about cylinder 1 piston, doesn't it look like a detonation?

The engine builder says it's only piston rings scratches and it's normal, but P2W clearance and piston skirts are fine. What do you think?

Thank you in advance for any comments and recommendations!

Kind regards







Attached Files

UPD: I'm mostly worried as I saw quite similar scratches via endoscope when I first got that engine built by the previous owner. When we first removed the head and then got pistons out, all of them had lots of scratches and didn't look good at all. And that engine burned twice more oil. I have a strong feeling that I'm getting back to the point I started at.

Attached Files

Two initial questions -

are you running an air filter and, if so, what type is it and where is it taking air from

did the "engine builder" give you any information on what (s)he claims to have set the piston to bore clearance at, and how did/does that corrolate to the official figures? I suspect that wear in on the major thrust side, and may be due to too large a clearance.

Hi Gord,

Thank you for your reply! Yes, there is an air filter also from day 1 after engine rebuild, I have GTX45 turbo, there is a 6 inch pipe to relocate the filter in the engine bay and K&N cone filter is installed, I do not have the exact part number, but it's a "dry" one. I inspected the intake pipe between filter and turbo a few times, it was pretty clean, no sand inside. Turbo wheel also looked good and I could not see any damages on it. OEM filter has a box connected to a pipe in a front left fender. I don't have the same box, although a filter is still located in the same place. There is a minor shield between the engine bay and filter and also an extra vent in the hood.

Unfortunately no, I will try to figure it out, all I have is ROSS job card and all the recommended clearances, but I do not know the correlation between recommended and actual values. Yes, you are right, it's not clearly visible on the pictures, but all 6 cylinders have exactly the same scores on thrust sides and other wall regions are good (at least I could not see any scores via endoscope) and hone is also clearly visible there. The only difference between cylinders I see is that 3-4-6 have "washed" pistons next to walls (e.g. cylinder 1 piston does not look the same), but as for scores - they are +- the same in all cylinders.

Do you suspect pistons slap as the major issue?

What I also noticed is that according to EGT readings cyl6 both idle and cruise temps are less than 1-5, especially while idling (~50 degrees difference). I suspected an EGT probe failure, checked it's installation and depth inside the exhaust manifold, seems fine, after I checked the temps using heat temperature gun and thermal camera and confirmed the difference. Spark plug also looks different as compared to 1-5 ones (please see photos attached). But it seems it's a different story and not related to scores.

Attached Files

One more question - how do you think, is it a good idea to remove the pan and probably oil filter to inspect ones for metal? Oil was changed twice (~300miles and ~1500miles after rebuild), current oil has ~1500 miles. if there is an issue indeed, can you see any signs in the oil/filter/pan?

The scuffing looks significant to me, but it's hard to tell exactly how severe it is from pictures.

There seem to be signs of significant oil getting in the combustion chamber and perhaps fuel going the other direction which can cause the scoring.

Anything you can do to improve ring seal will reduce fluids ending up where they don't belong. I've generally found tighter gaps and PTW resulted in less of this sort of wear.

Forgot, any scratches are from material finding it's way between the piston and the bore - that's why I was asking about an air filter.

There shouldn't be any such thing as "ring scratches" - not only would that suggest the rings' outer edges are rough, but that the oil film is breaking down. If anything, it suggests dust and/or dirt left in the engine during the build - I had a very experienced friend with an engine machine shop, and he had a large sign on the wall with "The Three Rules of Engine Building - Cleanliness, Cleanliness, Cleanliness" - the point being dirt or debris, even too small to see, can destroy and engine, or limit it's efficiency.

That said, the boroscope does magnify and flaws in the bore walls, and the slight leakage may be insignificant in practice - a cylinder leakage test will tell you more.

With the oil, some consumption is normal, and some engines are known to be worse than others, do you know what's "normal" for yours? IF it's getting into the cylinder (I assume you've checked for external leaks?) there are three basic ways it can happen - via the engine breather if directed to intake PCV, through the valve guides - most likely intakes as they're under vacuum at light throttle, or past the rings.

With the breather(s), checking the hoses are clear and not blocked or kinked, correctly routed, and the valve9s) are operating freely is about the best you can do - you may be able to disconnect parts and look for oil staining that might suggest excess? With valve guides, depending on the 'scope, you may be able to bring the intakes to fully open and look to the backs of the valves to see if there is an indication, such as a build up of deposits and repeat for the exhausts. Another indication is the deposits on the spark plugs - if you can mark, or otherwise note, the position of the spark plugs before removal, and one side had more deposits, that can suggest oil is coming into the cylinder from that direction, but if there's an even build up then it suggests it may be from the rings.

You don't show the others, but if only #6 looks like that, it may be down to some oil entering the cylinder, a rich mixture, and/or a light misfire

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