Got Bored---Engine Looksee

Got bored so swapped out plugs, did compression/leak down and played with the new borescope which is not top quality and couldn't get pictures of the valves. But does have a side camera and have close ups of the pistons. Unfortunately my lack of experience limits my interpretation on what I see in the pics.

Engine is a Livernois 298ci Short Block Stroker (Mahle pistons) 9:7:1 compression with 93K. Compression and leak down seem good. I have more pictures of each cylinder but didn't want to post too many pictures. How does this look to you guys?





Cyl 1


Cyl 2


Cyl 3


Cyl 4


Cyl 5


Cyl 6


Cyl 7


Cyl 8

The dark, vertical lines in cylinders 7 and 8 don't seem normal to me, but I guess they are since they are in all cylinders to some degree. You can still see the bore crosshatch, but it almost seems like something got stuck between the rings and scraped up and down for some time to create those lines. I'm probably wrong, but that's what I thought.

Very little carbon buildup for and engine with 93K so you must use quality gasoline yeah?

Rich said:

The dark, vertical lines in cylinders 7 and 8 don't seem normal to me, but I guess they are since they are in all cylinders to some degree. You can still see the bore crosshatch, but it almost seems like something got stuck between the rings and scraped up and down for some time to create those lines. I'm probably wrong, but that's what I thought.

Very little carbon buildup for and engine with 93K so you must use quality gasoline yeah?

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These are pics with the side camera of 7 and 8. The lines concern me as well, but they are similar in all 8 cylinders. Wonder if it's carbon vs. actual scrapes. And yes, only use 93 octane from Exxon.

Cyl 7


Cyl 8

Yeah, what you said about carbon makes sense. If it was something stuck between the rings then it would have gouged it and that's not what I see here.

You can get this with overheating or bent rods. No machine shop will let you get away without a rebore.

If those vertical marks line up with the piston skirts, That looks like the results of a thermostat that is too cold or running the engine hard before it has fully warmed up.

Stock T-Stat and I always make sure the motor is up to temp before getting on it. It has overheated a couple of times due to fan or water pump failure but I've caught it right away and shut down...not that it wouldn't have caused issues, but none that have been apparent. Car runs perfect, just trying to keep learning and those lines in all the cylinders are worth asking about.

Every engine i have ever opened up had those marks. It is the skirts on the pistons that make them. I doubt if you pulled the head that you could even feel them or measure them with a mic.


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A machinist will insist on a rebore.

LarryJM said:

A machinist will insist on a rebore.

Click to expand...

They always do!

Have you ever taken an engine block to a machinist that they didn’t want to bore it?


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Mach2burnout said:

They always do!

Have you ever taken an engine block to a machinist that they didn’t want to bore it?


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Click to expand...

No never. I purchased a core short block for $50 that had the same thing. I could not feel the scratches and it still had crosshatches. Brought it to the machine shop to be disassembled. It was already .030 over. The rods were bent and pistons out of round from overheating. Cheap good forged pistons were available for .030 over but the same cheap good forged pistons were very expensive more then .030 over. Like $15 each for .030 over and $60 each of .040 and .060 over. He said he would not guarantee his work without another over bore. The crank was beautiful. In the end, I did find .040 over on sale. Another machine shop did the work.

Scuffing from the piston skirts, the limited lighting from the camera makes it look worse than it is.

Scuffing like that is not normal, especially if it was bored and each piston bore was honed to fit each piston.
Are the witness marks on the thrust side of the bore or both sides of the bore? So, for me either the pistons weren’t fitted to each bore, or no deck plate was used when boring or possibly rig gap wasn’t where it should have been, but the marks are not a good sign. How many miles do you have on the engine since it was built.
Here is a picture of one of my 408w race engines after 5 seasons of drag racing, no witness marks in any cylinder.

I've seen those marks on a borescope only for them to practically disappear once the cylinder head is off.
Also, the skirt design is different on a mod motor than a windsor so apples to oranges as a comparison. Piston scuffing is very common in mod motors.

Very tight P to B on some mod motors. Mine was not! I had one hole with such marks, much less crosshatch than I'd seen in other engines all over - but I put it together w/o touching the bores with new OEM type Mahle rings on the stock pistons and it is the best engine I've ever built. The oil stays CLEAN, tons of power, no blowby.

I'm currently assembling on a LONG timeline (have a new baby) a 6.0 LS (used) and the bores were fairly awful, scoring on one and staining, I actually used green scotchbrite as an experiment - can't wait to find the results on ring seal, I'm not taking the short block apart at this time just to see how it runs. Will be hot and WOT from the get go.

Motor has 93K miles and about 200 1/4 mile passes. Built and bought straight from Livernois. The marks are consistent around all 8 cylinders. I know the pics are crappy, but they seem to be less scuff marks than they are deposits. Some have even faded/cleaned away with no effect on the crosshatch. Maybe I'll send the pics to Livernois and see what they say. Once again, this is only an inquiry/learning post vs. identifying a problem. But if I caught an issue early, even better.

Bore scopes make images look worse then they are. There are tons of papers / journals written on the topic from medical use to automotive. Stick with the leak down test.

Most engines I’ve seen apart have some degree of scuffing on the bores. You have what looks too me like good compression overall but four cylinders have more than 10% leek down. I would run it until it hit 20% leek down.

I would be more concerned with the leakdown%. Even with 93 k and the dragstrip activity that seems excessive. A well built performance engine will have no more than 5% when new, after break-in. The vertical marks can show up in a less than perfect piston/bore fit. And, if the piston fit is less than perfect, the ring seal will be less than perfect too.