Ring fitment question

[siteunseen]

I have an F54 87mm overbore block with some new 87mm dished pistons. I know that 1mm is .040" but the ring set that came with all this is .030" oversize. Is that what I need or should I get .040" oversize rings?

Thanks for any help,
Cliff

[cbuczesk]

You can put them in the bore and see if they fit. Maybe someone put the correct rings in the wrong box. But odds are that you'll have to get 40 over rings.

Chuck

[siteunseen]

Turns out I was dead WRONG. Bought a 240 that came with these parts to build another motor, 2.8 with an E31 head and some triple Webers. I was so excited to get the car I wasn't paying much attention to the parts that were part of the deal, car ran great as it was.

So now I've measured and am pretty sure he bought .750mm over sized cast piston cups. The block was bored .030".
Here's the numbers as best I could get, block bore is 3.410". Pistons measure 3.390". Top ring in the hole has a gap of .026" with a feeler gauge. Piston with top ring, in the bore looks pretty darn close, very little wiggle.

I'm going to put it together with an E88 head that will have the bigger valves put in. It's an early E88 so it should have good enough compression with the dished pistons.

Sound OK?

[Zed Head]

Never been that far in to an engine myself, but all of those numbers are in the Engine Mechanical chapter. Nissan was very thorough, they even have the .50 and 1.0 mm oversize numbers. Bores, pistons, ring gaps, the works. No 0.750 though, you'll have to split the difference.

Looks pretty good from a words and numbers perspective.

[siteunseen]

It probably is an 86.5mm but there's a "0.75" stamped on the piston tops and I can't figure what else that could be???

I know I could load it all up and got to a machine shop and know for sure but that'll be later. I'm trying, with the help of the members like you, to know as much as I can about this motor. I like the dished pistons for pump gas and it's going to be temporary until I get the original 2.4 built up nice and shiny with the E31 head I'm gonna sink some dough ray me into, $$$. Just getting ready for the cold weather projects I've been putting off until it cools off, and it finally has down here.

[Zed Head]

Isn't actual measured clearance what matters? Actually I missed a zero and you might be too loose. 10 thousandths versus 1 - 1.8 thousandths spec. My mistake.

(3.410" - 3.390") /2 = 0.010"

The ring gap looks okay though.