heptadecagonal hone job - Howdy Doo-it ?

[BillK]

If you look closely you can easily see where the top ring stops at top of travel. There is no funny pattern at top of ring travel. The odd wear pattern doesn't start until the location of the oil rings. If there was a surface texture issue wouldn't the top rings also highlight it? Never once in 40 years of building and freshening race engines have i seen a sunnen hone produce such a finish. i think the oil rings are the cause of the shiny stripes.

Good catch And it verifies what I said that is is probably the oil rings.

[hoodeng]

It is interesting that the oil ring has been called as the culprit of the anomaly, it could well be, due to the location of the bore marking as pointed out by others. Is it possible that due to the rings tension and rail sections it has highlighted the bore condition and the comp rings have not? Could the bore condition possibly extend into the comp rings path to the top? And not finish at the end of the oil rings path, i would expect a change of appearance at the end of travel, feathering out, more/less irregular appearance? I'll put two dollars on the bore condition extending to the top and it's the oil ring only that has highlighted it.
I have not seen longitudinal corrugation in a bore before caused by a ring, the most common damage to bores by 'Cord' rings is usually horizontal corrugation. The most common cause of longitudinal error is finishing. I am prepared to learn though!

The second photo shows the phenomena being highlighted by light being passed under the piston and what i assume to be one of the compression rings installed, the appearance is more than visual, but a noticeable even bore diametric variance. If all the rings have taken a set in shape this can be checked by installing the ring in a groove, chucking the piston and then rotating the ring with a dial indicator on it.

Cheers.

[modok]

It's plausible. hopefully Bill will get back to us about that.
It should be easy to tell if the worn spots.... are the high points or the low points.

[BILL-C]

Cylinder pressure gets behind the top ring and forces it out against the cylinder wall on the power stroke. The cylinder pressure is the highest at the top of the stroke and this is why we typically see the worst wear at the top of the bore. If there was a bore geometry issue at the top of the bore it would be highlighted by the top ring the most. I have come across this issue before but not so extreme. The problem was the chrome plated oil ring scraper rails never got polished properly and had some nasty teeth on the od.

[Jpat]

I just wanted to update and provide new information for this thread. This engine belongs to me, Dan encouraged me to join the forum after he posted the images for me.

Some background- this is an LS3 based stroker that had a 4" K1 crank, scat 6.125 H beam rods, and srp flat top 4032 pistons (part number 329372).

I acquired this engine as a short block, very cheap from a local performance shop. It was removed from a customers' car due to excessive leakdown on cylinder 3, the striped one shown. The leak was determined to be to the crankcase by the shop, and the customer elected to replace the engine rather than diagnose it. The mileage was extremely low, to the point the shop thought it was either a stuck ring or a bad break in. I have measured to bore to be 4.076-4.077 on all 8 cylinders, which looks like it was supposed to be bored .010" over.

I have attached additional photos. The stripes do go beyond the oil rings, as shown below. The are visible to the top of the compression ring travel.

20210923_191651.jpg

Also, multiple other cylinders show faint striping, but not nearly as bad.

20210923_191725.jpg

20210923_191717.jpg

20210923_191704.jpg

I also did the "light test" at the bottom of the bore, below where the rings travel, which indicates to me it most likely was a result of the machine work, not caused by the rings.

20210923_192201.jpg

[KnightEngines]

I had a factory ls2 block come in like that, it'd never been apart & all the bores were like it.
Dealer job for oil consumption on a used car.

[Jpat]

I had a factory ls2 block come in like that, it'd never been apart & all the bores were like it.
Dealer job for oil consumption on a used car.

Interesting. Did you rebuild it?

[KnightEngines]

I had a factory ls2 block come in like that, it'd never been apart & all the bores were like it.
Dealer job for oil consumption on a used car.

Interesting. Did you rebuild it?

Yep, honed .005" over with torque plate, new pistons & good to go.

[agertz1]

FWIW, tech at Total Seal, said my 1/16" rings, street use, .010" OS., would file to fit just fine, but MUST file the oil rails !