Cylinder overhaul or new?

[67Porsche911S]

I have my 2.0S engine dismantled and everything looks like it should be for a low mileage of 26.000. The engine wasn't running for a long time and I have some dark spots on some of the cylinder walls:

You can't feel them, its only visible. The measurement of the cylinder bore and the pistons is ok. My engine builder suggests to go for a set of new cylinders and pistons 'just in case'. I am not sure if that's really necessary as the original honing traces still there and everything looks fine otherwise. I am thinking of just rehoning the cylinders and put new piston rings on.

Has anyone an idea what these spots are and what's the best to do?

[304065]

Michael, those are probably just oil stains.

Accurate, precise measurements of the cylinder bore at multiple points is critical. Measure that very spot-- is it lower than the rest of the cylinder? If it's really 26,000 miles, you shouldn't have the problem unless the engine came to an abrupt stop (catastrophic failure).

I would progressively clean the cylinders-- a good bead blast of the fins on the outside followed by a scotch-brite pad dipped in motor oil on the liner. That should make things look much better. If you want to hone, OK, but I would do it only to break the glaze and reestablish a cross-hatch on the liner.

Of course you could bore to 81 as I did and use custom JE pistons, this results in a tiny displacement bump (50cc) and you can make the piston dome 0.8 cc smaller (very slightly less height for better combustion) but if the measurements say you are OK, I would clean up what you have and use it.