[Dpmulvan]

Originally Posted by Thorndyke

I am pretty sure that I need to replace piston rings, but posting this just to make sure that I am not missing anything.

Background: engine is 1978 911SC 3.0, 180k miles, totally stock, it looks like I am the first one to open up the engine - under each washer the metal isn't just clean, its shiny. It was running really well, but I have the cylinders off to replace broken cylinder head studs. It did not smoke on start-up unless it sat for more than a week. Plugs were generally clean, but the car is new to me so they might not have many miles on them. Insides of intake runners were really oily though. I had not done a compression test, but the leak-down test generally good, mostly at 4% but one cylinder at 7% and another at 11%. I will keep the car generally stock, and it will be entirely street driven (except that I might do some PCA driving events).

The cylinders look great inside, crosshatching throughout. The gap between the piston and cylinder is too small for me to measure with a feeler gauge. I don't have the bore gauge to directly measure the cylinder, but measuring it the wrong way (calipers!) showed like-new measurements top/bottom.

Piston ring end gap on the top two rings is very large though - over 1.25 mm. Based on wear limits, seems like the only choice is to replace them, and clean/"deglaze" cylinders. Is that a correct assumption, or is there any reason that I would want to re-install the old rings.

The reasons I ask is because of reading discussions on new rings having gaps larger than specs (to reduce chance of too-tight rings from damaging cylinders), and getting new rings to settle in with the old pistons without honing (just "deglazing"). Still, 1.25+ mm seems excessive and at this point I am planning on new Goetze rings.

Pardon the long post, and thanks in advance for your opinions!

1.25mm ring gap can’t be right, I bet your actual ring gap is closer to .017 or .018.